i recently purchased a 1999 toyota 4runner and i was convinced the lean condition was from the awful exhaust leak i could hear coming from the manifold. no one believed me. after inspecting this weekend, i realized coming down from the manifold just before the first o2 sensor, it wasn’t bolted properly and there was a gap between the two pipes. like you mentioned, all the data pointed towards a vacuum leak. at idle, fuel trim was plenty into the positive (higher than your findings here as i literally had a gaping hole), while under load the vehicle’s fuel trim nearly evened out. that being said, i still thank you for this video. two of the people who suggested it couldn’t be from the exhaust leak are mechanics. they aren’t nearly as familiar with fuel trim and reading data from an OBD scanner as i am, and you have been a huge help as a resource. i don’t think it’d be possible to differentiate the two (as you found in your video) but it’s important to understand that they have identical traits since they’re both unmetered air that can result in a lean condition. i hardly ever see it brought up as being a possibility with a P0171, and after asking around i’ve realized most people turn down the idea before exploring it.
I am an automotive technology student, working to get my certificate and then become ASE certified. Diagnostics is the best. Im not taking classes over the summer so I get my fix by watching your videos. Thanks for sharing the knowledge.
Thank you for sharing your knowledge here in your videos. I took the newfound knowledge and went to work interpreting my data. LTFT at idle is 14.5%, and S1-O2 at 0.780V. The readings level out at higher RPM's. The exhaust smells at idle as well as having a high NOX value on my smog test - that's what got me looking to figure this out. So I went searching on the exhaust side of my 1997 Pickup KA24E (Nissan 4 Cyl). What I found was a broken exh. manifold stud. Using propane to find a leak had no result/change. But the broken stud had me concerned, so I disassembled. The lower gaskets of the manifold were on the brink of disintegration. The upper gaskets were fine with no visible leak deposits. The O2 sensor had a white coating of baked on deposits too. Not excessive, but enough to alert me to a possible coolant leak internally (head gasket likely). But here's the interesting part. I cleaned/polished the exh. manifold. Had I not done so, I would have never seen the hairline crack in the Y where 1+2 & 3+4 ports meet at the lower dump. So with this newfound insight, I reassembled with new gaskets and have to order a new exh. manifold. I know you say not to throw parts at a problem, and it takes a big exhaust leak - which would be audible - in this case my truck isn't loud, but I do smell some exhaust in the engine compartment when I first open the hood. The hairline crack in the manifold warrants a new part, as well as new engine mounts - since there had to be a cause for the broken stud and cracked manifold. So I'll see if the new manifold corrects the high LTFT value at idle.
@Carter Edison New Exhaust gaskets helped. New O2 sensors helped as well. I did discover a hairline crack in the stock cast iron Exhaust manifold. As of this day however (23 years old and 225,000 mi), I am in the re-assembly phase of a completely new engine (Nissan KA24E) rebuild, and in doing so, I see the root cause of all the little issues... a worn out engine. I'd love to replace that mani with a new set of headers but there's this thing with the smog test in CA.
I experienced this condition with exhaust leaks downstream of the pre-cat O2 sensor. Pegged lean at idle but would start to run rich around 2-2500 rpm. After going nuts trying to find vacuum leaks I plugged some exhaust clamp leaks between the cat and muffler. After a test drive reading the o2 sensor and trims, I think that the fixed it. Thank you for the video
I was looking for information on this topic. I've been banging my head against the wall trying to find an intermittent lean code. I wondered about the significance of an exhaust leak. Your theory is valid. Great job explaining. Thanks man!
Right on the money, I have a ford expedition 2003 with that problem. P0171, I fix all vacuum leaks and smoke tested (under the hood, gas tank, and exauat pipe) and the code continues P0171 to show. Since Short trim continue to follow long trim however stay a 20 %, at high speed there is not a problem, when you lower around 1100 RPM an OPEN LOOP happens, since the delta between trims goes around 25%. IF continues I fault loop shows and the computer operates in OL. This is confirmed if you follow the Oxigen sensors. Today I went below Expedition to find 3 broken bolta at the exaust manifold at bank one. I watch your video on the 3D adaptative matrix and definitive make sense the computer will take charge to avoid flood the inyectors with gas due to a rigid follow up on the 14.7 to 1 golden rule. To notice is that is that a lower ambient temperatures the engine work smothly and nice, I guess is because the mass of air at mass afected by the IAT. It definitly one hell of diagnosis, Thank You for the videos, I have learn a lot.
Exhaust leaks explain themselves well, especially bf the cat. Technicians on the clock, expected to up-sell, and sell as many parts as possible, diagnose things differently. That's why since youtube offering a wide range of perspectives, all are important bc there's always diff details mentioned.
Thank you for your educational videos. Myself, I love science. Your way of explaining the diagnostic concepts is superb. I have spent over 2 weeks watching your videos on CZcams and its been great. I have learnt a lot. My car’s LTFT and STFT have been moving all over the place. For the STFT it goes as low as -22% and as high as +28% at different engine load conditions during driving. After watching some of your videos, I decided to look for vacuum leaks. I found one around the intake manifold gaskets, so I got that fixed. That stabilized the STFT and LTFT at idle. After sealing the vacuum leak, at Idle, I get between -3% and 0% on the STFT and a constant -1.85% on the LTFT. But when I increase the RPM the STFT moves randomly between -19% and +10% while the LTFT moves only slightly between -4% and -1.85%. Here are two examples I caught on the scan tool while driving: 1. At RPM of 1253, Air/Fuel ratio (lambda) of 2, STFT at 0% and LTFT at -2.34% (fuel system was in closed loop). 2. At about 2400 RPM, STFT was 0.78%, LTFT was -3.91%, Air/Fuel ratio (Lambda) was 0.98, O2 Sensor (B1S2) Voltage was 0.66 (fuel system was in closed Loop). I also noticed that the intake manifold pressure is 33kPa at idle. But when I increase and hold the RPM at about 3000, the intake manifold pressure immediately increases to about 47kPa and drops to about 28kPa although the RPM is at 3000. I don’t know if that is normal. The car does not use a MAF sensor. My car is a 2010 Kia Forte 2.0L 4-cyl engine with 121,776 miles on it. It uses an Wideband O2 sensor upstream and a narrowband O2 sensor downstream. I often feel a hesitation in the engine when I depress the Accelerator pedal. Can you please suggest what the problem might be or further tests I should run?
Hi Matt I believe there is a direct correlation between intelligent content and intelligent responses from participatory viewers. I have yet witnessed such intelligent and respectful contributions on other CZcams channels. I think the only way you can learn is to engage as many people as possible. Good for you Matt for providing a unique venue for learning thru you and your viewers. Thanks 😄
Steve Rob That's how we roll! If you like the format and philosophy the channel follows- stayed tuned for "Schrodinger's Mailbox" first episode coming soon!
Matt. Not a wate of time at all, because the conclusion is valuable. If you have an exhaust leak that is causing a lean condition you can more than likely hear it. That is valuable!
Thanks for taking the time . Quite the experiment. All my grief is coming from, bank 2 o2 sensor 2 . Went from a 430 code to lean , low voltage codes. Cat looks good. New o2 sensor stays at 590mv others about 200mv higher. Car seems to run fine I just want it to quit throwing codes.
looks like it’s stuck at bias voltage to me. check your bias voltage and compare to the O2 voltage. also induce a lean condition and see if O2 responds accordingly.
A good physical inspection is always a good place to start. Currently I'm dealing with a similar issue on a 2001 GM 8.1 with high long term fuel trim on bank 2. A quick visual inspection revealed a leaking manifold to pipe gasket on bank 2. This leak actually draws air into the exhaust by the venturi effect causing long term fuel trim to advance to plus 20 percent. Diag by verifying and repairing exhaust integrity before any fuel trim diagnosis can continue. Once exhaust integrity is verified retest revealed stable normal long term trim numbers. If you're customer doesn't want to fix the exhaust leak you can not continue to diag it verify correct operation and your job is done.
So you heard the exhaust leak and checked for a leak at the exhaust? Yeah, I would have done the same. Especially AFTER checking fuel trim and determining there is an unmetered air leak on only one side of the vehicle. Of course its a place to look. Now if you did a visual inspection without knowing the fuel trim analytics and found that- I'd be impressed!
Sorry I should have also said great content and thanks! Stuff like this is how I built my first 302 from the ground up, only using youtube and a couple of great friends. This kind of content is sooo underrated. Thanks! 👍
Very helpful video. Prior to viewing this video I never thought an exhaust leak would behave like a vacuum leak on fuel trims - creates a lean condition at low rpms. Good news for me because it is now less likely that I have an exhaust manifold leak since my scan tool reports a lean fuel trim condition at high rpms and a neutral fuel trim condition at idle. I have two banks and one has twice the change of the other so it is not a fuel pump issue. Now to turn my attention to lazy fuel injectors.
having exhaust gas leaking around an O2 sensor will cause it to misread. Remember, an O2 sensor must sample the oxygen level of the ambient air (without dilution from an exhaust leak at the sensor) to work correctly. My understanding is the same principle applies for both wide and narrow band zirconia sensors. I believe you would need to induce a leak well away from the sensor to make this a true 'scientific' test. Your videos are very informative. You're diagnostic skills are first class. Cheers.
Hi, I've been doing similar testing. I found that partly blocking the exhaust can be seen on the O2 sensor reading and STFT, if they have been altered because of an exhaust leak. I believe the theory behind this is that as the exhaust does in effect pull oxygen inside when a "negative pressure" wave caused by air mass is induced inside. This will not happen if the pressure inside the exhaust is greater than that of the surrounding air. The blockage shouldn't be too large or be kept for long though, as It will slow the speed of the exhaust and cause problems with exhaust gases leaving the cylinder.
Spent two months trying to find why my foxbody was surging/fouling out plugs. Turns out the slip tube on my new long tube headers had a massive leak. No CEL at all but ended up getting a passenger side lean code during KOER test. Created a vac leak and bam confirmed diagnosis.
Der Matt First: Great Channel After watching all Your Videos and learning a lot I have a problem concerning exhaust leaks. As an engineer by training and an Airline pilot by trade, Physics dictate that an exhaust can only leak from the inside out. There is always a higher pressure inside the pipe than on the outside, else an exhaust would suck air into the tailpipe. Now for Your experiment,You had to take the O2 sensor more or less out to get a lean condition. At this point You are exposing the sensor to the oxygen rich outside air and hence the lean condition starts to happen. To eliminate the possibility of a mistake on my part, I drilled a hole into an exhaust (junk car, but engine still running) and airflow happens alway to the outside only. Everything else on Your channel is great and has improved my troubleshooting and understanding a lot. Also I have resolved the P0105 on my wifes Jaguar, and it sure was not the MAP but a serious carbon deposit in the throttle body bringing the TPS out of idle limit. Great, great, great since they would have NEVER found it at the shop. Keep up the good work and if You want, You can reach me via email, bernhardlist@hotmail.com sincerely, Bernhard
Bernhard List Pretty good analysis however a couple things: While the pressure in the exhaust is higher, I think you are not accounting for the theory of vacuum by the Venturi effect (Ironic, seeing as how you are an engineer and pilot since Bernoulli principle is involved in that). This in fact accounts for the reason you do not have vacuum at the end the tail pipe (which you are correct about, but Venturi effect no longer applies at the end of a stream) but would theoretically have it along the tailpipe. What people are claiming is venturi effect causing vacuum of outside air. Exhaust "Scavenging" is another example of this for those into high performance applications. So I think you overlooked these physical concepts/laws in your analysis. Second, your experiment did not describe how you eliminated that possibility that there was venturi effect. And third, just in a grammatical sense- the sentence "As an engineer and pilot... physics dictates" indicates that the laws of physics are dependent upon your education and career choice. "As an engineer and pilot, my understanding of the laws of physics would indicate" would be proper poisitioning.
Bernhard, I've got a P0105 on a 2004 Jaguar s-type 4.2, and was curious where your carbon build up was and how you cleaned it. On these vehicles i saw somewhere the MAP is really just monitoring the EGR, which i thought might be clogged with build up. Thx much.
I've been fighting with an exhaust leak because I thought it was the cause I'm very glad about your findings because this thing is impossible to drill the bolts out of the manifold and I don't even hear it.
2003 Mach 1 Mustang, took it to a Pro Exhaust shop to have a SLP X-pipe installed. Instructions said to remove drivers side manifold studs and use bolts which they did not do. Drove around for a year with an exhaust leak. Could smell fumes and it finally threw a P0174 code (lean, bank 2). Fuel trims were way outta whack for bank 2 which triggered the service engine soon light. Took it back to the exhaust shop and they made a shim vs removing studs. A few days later got a P0171 (lean, bank 1) because they loosened passengers side to fix drivers side. Mechanic said if code came back to purchase a Ford manifold flange gasket.
Great video as always! So basically if there no abnormal exhaust noise, the lean condition is something else. I have a Corolla that is leaning STFT is about 8% LTFT 14.2% with some bad fumes around the car and with the heater running so someone online told me to check for exhaust leaks despite the fact that i don't hear any abnormal exhaust sound.
Yes, exactly! My findings show that you have to have a significant leak to get the false lean response. I would recommend curving your fuel trim against load to better narrow down the cause.
Okay, so you may not have created a new test, but the information was new to me. Whenever I see fuel trims that say intake leak, I should listen/feel for an exhaust leak. That had value to me. The doubter in me is going to feel for an exhaust leak until I see it for myself. I realize that your test showed the leak would have to be very significant and therefore it would be heard. Upstream of a cat, I've seen exhaust leaks change data a GREAT deal, even on small leaks, so it's effect on a P0420/430 may be more significantly definitive by sensor data alone than a pre-upsteam fuel/air ratio sensor.
A caveat occurred to me when I woke up in the morning, that an O2 sensor may more easily react to a leak at the same spot than an air/fuel ratio. Since the Air/Fuel ratio supposedly actually sees the ratio of air to fuel, that ratios could be the same whether it's leaking or not. Perhaps, the difference for an O2 sensor reading a much smaller range would be more sensitive. The other analogy that occurs to me, is that the exhaust escaping over the Air/fuel ratio sensor, the escaping exhaust may be acting like shielding gas on a weld. It still wasn't seeing much atmosphere because it was getting covered by the leak. Leaks elsewhere can still be theorized on how they'll look based on this fine experiment. This does suggest that this leak may have had to be bigger to see the effect.
Sure you can, it's simple. A quick check I like is to watch fuel trims/O2 activity at idle and have a helper stop up the exhaust then see if trims/activity change. I see this on vehicles with broken bolts at the manifold. If you stop it up you create positive pressure in the exhaust system. This prevents any air from getting sucked in through a leak. If you take away that air, then the trims should shift downwards. One thing to remember on your smoke test from the rear. You'll never get enough smoke through the cat to ever see it. so anytime your actually looking for a leak, pull the front o2 and smoke it there, or if it's a ford, pull the rear DPFE hose off and smoke it there. Remember, you can barely see daylight through a good cat.
Sorry to differ but you're dead wrong about the smoke test. I have detected EGR valve leaks, manifold leaks and in fact AIR leaks with smoke to exhaust pipe- as have dozens if not hundreds of my viewers. In fact it is amazing how quickly the system fills. As for the blocking the exhaust, that's a great idea however I will need to try it with a negative control by blocking the exhaust without an exhaust leak to make sure full trims dont shift downwards just from the blockage.
Schrodingers Box Ahhh, when have I ever let you down. I have 2 of the same smoke machines you have. Put yers on a late model F150 and then get back to me on how "quick" you get smoke up to the DPFE sensor :o)
You wouldn’t hear the leak on the turbo to downpipe exhaust gasket on for example…a European “hot v” engine such as the ones made by BMW and Mercedes yet this Will perfectly produce the fuel trims that you were trying to achieve.
I’m suspecting an exhaust leak (can’t find any intake leaks) on my Nissan 3.5. What throws me off is the car basically fixes its fuel trims during a cold start up and initial warm up, as well as highway driving. The problem is most detectable during long, hot idle. That’s when the STFTs jump upwards of 10-15% on both banks, on top of the already high LTFTs (10% and slowly going up as the car keeps idling). I haven’t tried leak testing the exhaust yet.
I agree with your findings that with an exhaust leak at the sensor, or for that matter a leak at an exhaust pipe/header flange connection, there would be minimal effect on fuel trim. However, an exhaust leak at the exhaust manifold (with either a crack or a leaking exhaust manifold gasket) near the cylinder head there will be a different result due to the proximity of the individual pulsations caused by exhaust from each cylinder. As the cylinders are exhausting, particularly the ones on an exhaust manifold that are downstream of a crack, they will induce a vacuum to draw in oxygen at the crack.
johnwrench4speed Hmmmm, I will have to test that- but no way I'm doing that on my cars lol. And not because I want to induce a leak, but more because the manifold is not accessible on either without much dismantling. If I ever get a chance, I will induce a exhaust leak at the manifold on a car if I get a car where the manifold is easily accessible.
+Schrodinger A few ramblings... The STFT increases when the "exhaust leak" is induced. The rising A/F signal causes the PCM to *BELIEVE* that the engine is running lean when in fact it is running rich due to STFT correction. This should generate some additional activity (heat) in the CAT due to the additional fuel. This heat increase may not happen to as great a degree if you were to induce an intake vacuum leak. In that case the engine *REALLY IS* running lean and the STFT is bringing the engine back into stoichiometric balance. At stoichiometric, the CAT might be less active (cooler?). This observation is only useful as an exercise in the case where we know there are initially no leaks and we induce one to watch the changes (i.e. the CAT heating up). It is still not helpful in differentially diagnosing whether an engine of unknown initial state has an exhaust leak. I agree with you that an exhaust leak will be heard long before it becomes serious enough to affect fuel trims.
I still wouldnt rule it out an exhaust leak even if you cant hear or smell it. I had a leak on both banks (2013 Taurus), which couldnt be heard(or smelled? Idk my nose is shit). It improved fuel trims by about 10% but LTFT is still high at 16%. So I may have both exhaust and intake leaks.. I will find out soon.
If you just change the MAP sensor and hope for the best, it won't matter what you look for next. If you are just going to just guess at parts without diagnosing if they are faulty then there is absolutely no reason to try to put a methodological systematic strategy to it- because it's impossible. Just guess and swap on a whim. But I'm not sure what you are doing on my channel if that will be your decision after I made 78 videos showing conclusively how that is the wrong strategy. Nonetheless if that's your approach, I guess one strategy might be to post your symptoms on any automotive forum- you will get more ideas on what to swap than you will be able to afford. And as long as your hoping for the best- instead I would hope it isn't a vacuum leak- because no parts changing will fix that. Of course even that is illogical- hoping that something is not an etiology has no effect on whether it actually is or not.
I am going to take truck to have a nother complete diagnostic test tomorrow.I assumed a diagnostic was to pin point the problem or steer a person in the right direction.your right I'm not going to keep guessing.
check engine light on. Wish it was a different code or even a 2nd code with this one. Got a P0171 code (lean air in bank 1) parts that have been replaced within the last few years or within the last few days.... EVERYTHING YOU COULD THINK OF!! cold air intake hose, spark plugs (#3 had oil on top of the spark plug and boot - spark plugs replaced- boot cleaned off - access oil inside clean up.) Had to replace the valve gasket? Pretty sure that's what it's called. No air leaks. Both 02 sensors replaced. Maf sensor replaced. We are waiting on an exhaust manifold comes with gasket for that area too. The bestie says we need check the intake manifold. (Kinda waiting to do that cuz it looks like it's going to be a bitch) car isnt over heating. Idling... kinda rough... the fiance and I knew the exhaust manifold was going to need to be replaced. But... really could it be the intake manifold?
This is why California needs to do away with emissions regulations. Codes like this will bankrupt people. We just need to get to live our lives... Car runs great why should it matter if there's a point .001% error in it's air fuel ratio. Come on California you are killing us!!
This is actually common on the 2v tritons. The superduties seem to be the most sensitive to it because of the nature they are used for. It can cause flooding out if the leaks are bad enough because the computer is constantly trying to richen the fuel up, my farm truck is throwing that code currently because of manifold leaks and a bad y pipe. The previous farm truck that was wore out I would occasionally have to shut it off for 4-5 minutes to dry the cylinders out otherwise it wouldn't have enough power to go past quarter throttle.
Mind you the flooding situation was only with a loaded trailer where there is a excessive load on the engine, just driving 15-20 miles was no problem but you could smell it was running extremely rich. Fuel pumps can cause a similar situation except for it won't run rich it just won't have enough fuel to do more than idle.
Ok, in case there is a language problem, please ignore that, since my native language is German. I might not be too exact as far as my grammar is concerned. (I will not spell vacuum, VACUME, ok) I am writing this answer because: 1) as far as aerodynamics are concerned there is always a specific shape (airflow across a wing or through a venturi tube) involved that I could not find in any exhaust. 2) any pulsation would average out (just my opinion, no proof). 3) I am not trying to come up with new theories, so I did drill holes into the exhaust before writing (I do agree with You about testing first) and the holes in a Saab 900 exhaust blow air out anywhere I drilled (and it is hot :-). I know there are airflow problems in intake systems (standing waves) and this may well be the same with exhaust pipes but I could not produce any vacuum anywhere and in Your video You had the same problem. If You are able to show any vacuum in an exhaust system, I will gladly erase my comments. Greatings, Bernhard
Agreed- neither of us has proof, You are correct indeed that I also failed to demonstrate my theory as well. I have long been waiting to revisit this video and do exactly that- will keep you posted. I was just pulling your string on the grammar thing, no offense intended.
Matt, I guess that snuffs out my idea of a small exhaust leak on that 320 hp Beast of yours! I have to agree with you. After you had to unscrew the O2 sensor ( Wide Band ) all the way out to get any noticeable effect on the Trims, that a small leak is highly unlikely to cause a lean condition. That still doesn't mean I'm giving up on a bad O2! I went back and reviewed the Scan Data in the last vid ( Test Your Lean Condition P0171 / P0174 Diagnostic Skills! ) several times, to see if I could spot any abnormalities in the traces. I notice that in your garage, on frame 5220 on the LTFT, it was showing a lean condition and adding fuel.The STFT was taken fuel away, like it should, when you were opening the throttle plate. At the same time the Bank 1 O2 and Bank 2 O2 was oscillating from full lean .100 mv to full rich .900 mv, but the Bank 1 O2 seamed to be way more active and had tighter oscillations then the Bank 2 O2. Then at frames 5440 thru 5500 LTFT showed lean again and started adding fuel, but if you look carefully the Bank 2 O2 seems to again be more active then the Bank 1 O2. I could not make out what frames you were on when you were on the road, but if you look real carefully the same seams to occur, just not as severely. I still betting on a bad O2 on Bank 1. Also, when you first came off the throttle stop in your garage, I thought I heard the engine stumble, both times you did it. If that is so, that would definitely justify that injector balance test. Question for you. I don't own Autoenginuity, but Why don't the frames on all three graphs match? Are they set to different scales?
Billy R Billy first of all, 320HP? Really? What am I a riceboy? Jesus Billy. That car is 359rwhp and was Dyno tested to prove it at L.G. Motorsports in Plano, Texas a few years ago while I was on vacation. Now that the important stuff is out of the way, I agree with you 100%. Initially, my first thought was an exhaust leak on Bank 1 on that car and my second thought was weak O2 sensor (for those of you wondering what we are talking about this is in the video "Test your lean condition diagnostic skills"). But given the data from this video, I have virtually eliminated exhaust leak now. HOWEVER- look at JohnWrench's comment above which may change your mind back to exhaust leak.
Schrodingers Box First of all, let me apologize! 359 hp at rws, Wohhhhhhh, Don't punch me in the throat! I once owned a 1971 T-Bird with a 429cui V8 - 360 hp, came that way right off the showroom floor. Now them were cars! I maybe going out on a bit of a stretch, but as I was watching this vid, (Diagnosing Lean Condition from Exhaust Leak with Scantool P0171 P0174) and you came to the conclusion that you could not get the O2 to react until it almost fell out of the exhaust. I tended to agree with you, but something in my head kept thinking about airplanes. ( I love anything that flies) On a wing when the air on the upper side, due to its curved shape, speeds up faster than the air on the underside. The air on the upper side than becomes way less dense than the air on the underside and generates an immense imbalance or pressure/force called lift. Could this same phenomena be happening on your car. When your at idle, the pressures inside the exhaust are greater than the outside atmospheric pressures. When you start to come under a load and the gases heat up,expand, and speed up, are we witnessing the same effects as a wing demonstrates. As the gas speed up inside the exhaust and become less denser and the atmospheric pressure outside the exhaust become greater it would force air inside causing your lean condition long enough until the trims overcome the air coming in through a small leak. Most of your viewers are probably going to think that I might need a vacation or something, but you being a scientist, I thought you might see where I am coming from. But hey that is what this channel is about, to get your viewers to think out of the box, right! I know the most likely or conventional thought is a fuel delivery problem, but the way you romped on that bad ass 359 rwhp, it didn't sound like it was staving for gas to me! Now if you had oscilloscope, we could tell if that O2 was dropping out lean or not. Your scan tool is just not fast enough! Oh, by the way I like gojududes suggestion, Mattometer is awesome, but I would add Mad-Mattometer!
Billy R Wow, I wish I read Johnwrench's post before I posted mine. That man is on the ball! I salute ya John! Matt, you should never say never. You just might have to check out his theory to get to the bottom of your mystery! Let's hope not!
Technicall Billy, it doesn't matter that you read John's post after yours- you made a completely logical conclusion that was based on the data available you had at the time. It is the thinking that is most important, and you were dead on. As new data comes available, good thinkers have to reevaluate how this would affect their original conclusions- and you did that too. Data may come and go and be found to be inaccurate at any time but good thinking is a constant. So either way, you "get it" and are not wrong regardless what the problem turns out to be.
Thanks, Base on the symptoms or should I say lack of symptoms (No dry misfires/hiccups), the response of your engine and the fact that it is only effecting Bank 1, the evidence most likely points to either excess air is entering down stream from all engine sensors and up stream from the O2 sensor. There has to be a factual and logical explanation of where these extra O2s are coming from. Or you have a faulty O2 sensor! If indeed, air is entering upstream of the O2 sensor, I think Johnwrench's theory is more plausible and logical over mine. But it wouldn't hurt to do a injector balance test to rule out a sluggish injector (low fuel delivery) since you have ease of access thru the Schrader valve.
one tip to remember, if you can't hear it really good (but still have an exhaust leak) it'll set a P0420/P0430. The broken bolt/cracked manifold is common and is a cause for the P0171/P0174, but if they are set with the 420/430, then the 420/430 set first, as the monitors won't run with the lean codes set. In my opinion, this is your best vid. BTW, you don't get it named the mattometer or anything like that lol
Thanks GoJo but i cannot see how an exhaust leak could possibly cause a P04x0 code because there is no way it would cause mirroring of the front sensor (unless the leak came and went in perfect synchronicity). If anything the leak would prevent getting the 04x0 code even on a bad cat because the fixed lean signal would throw an O2 low voltage code and you cannot get a catalytic activity code with the other code set.
Schrodingers Box HI, Matt. I am also a scientist by day and auto repairer by night/weekend. I tend to do more collision repair than engine diagnostics, although I am certified in both. I really enjoy the videos and your approach to diagnosing and not just guessing as most tend to do. I actually had a car come in recently with a P0420 or 430, can't remember. The vehicle had just had the engine replaced (Cats working fine prior to engine replacement), and the shop did not reattach the exhaust correctly. This leak was audible and was the cause of the P0420. Just enough air was being pulled into the exhaust system to cause this. I can't remember which joint it was as I did not do the repair, but it was near the front of the vehicle. The shop was on the hook to redo it and the MIL has stayed off since.
Sam Graham Being that you are a scientist, did you validate that the rear trace was not congruent with the front O2 trace after the repair to confirm that indeed there wasn't ALSO a weak cat along with the leak?
I wish i had been able to, but i did not get the vehicle back after the repair. I see this customer weekly, and he has not gotten a MIL since. Not the most conclusive evidence, I know, but it made sense since there are pressure pulses in the exhaust that create vacuum as they flow through the system and the condition did not exist prior to the engine swap. Just wanted to mention this to you as a possibility in future repairs. Keep up the good work.
I like the idea of bringing diagnostic skills from another profession to auto repair. I've had the same kind of thoughts about new diagnostics for engine cooling systems, too. Problem is, some of the tools I would like to use (like doppler ultrasound to measure flow) would be a hard sell in a competitive market that can get by without expensive tools. To market a new diagnostic tool you need to show that it saves time or money.
Agreed- bringing diagnostics from other professions and integrating the tools of the trade is always interesting. I often wonder how a Gynocologist would approach some of these situations.
I should have watched this video earlier! This was exactly my problem on a 2004 Jaguar S-type 4.2 with 100k mi. Everyone kept saying I had a vacuum leak, because I had high fuel trims at idle which disappeared at load/speed . . . but just on bank 1. I'm a little deaf so didn't hear a slight "puff" exhaust leak at flange on Bank 1 . . . right before . . . cat . . . and wide band 02 sensor . . . One day my partner was riding in passenger seat and said "what's that noise?" It was so obvious once I figured it out . . . but only after doing every possible vacuum leak trouble shooting: blowing smoke in, replacing O ring on dip stick, propane around lines and into air intake to test O2 sensor watching for neg STFT, misting water, BK44, Scotty Kilmer's "plugs and wires" (I did plugs since I was at 100k anyway) . . and some stuff I forgot!. But deep down, it never made sense to me that a vacuum leak on the top of the engine would show up ONLY on Bank 1 elevated fuel trims at idle. I used a little Kroil and a breaker bar to free down pipe flange bolts and re-tighten . . . by hand . . . carefully . . .Hopefully I can be as logical in the future and avoid a bunch of unnecessary trouble shooting . . . and parts buying. But it was a great learning experience and I really enjoyed . . . thinking! I now know the mechanic I consulted at first (before watching your videos). . who pulled out the MAF sensor, cleaned it, and cleared codes. . . was an . . "idiot" . .. I believe is the proper techincal term. Now I just have an intermittent P0105 MAP code to deal with. Hence my question to Bernhard. Thanks Shrodinger!!!! I could never afford to own this jag if I had to pay for everything to be done to it! I am glad I didn't change the O2 sensor. But I am SO afraid to replace the O2 sensors . . .and get called an idiot . . .that I probably won't even when it ends up being the problem!
Dear Matt I really like Your approach to troubleshooting, so keep that up. Yours is the only channel I have subscribed too and I don't want to depend on Eric the Car Guy. I will be the first to watch Your video on exhaust leaks and I thank You in advance for finding the truth to improve problem solving, that is all that counts. With Lufthansa have been trained to troubleshoot a problem and not the captain alone decides on how we die :-)))))) Greetings Bernhard PS: Sorry we at Cargo don't have Denver in our schedule, else I would love to meet.
Many Thanks Bernhard. Yeah with your engineering background, ETCG is not going to be of much use for you. He provides great value, but generally for people who are beginners or need their hand held through a procedure (which is fine, most people by far are novices). But for people who know how to turn a wrench and what they need is advanced theory and background on automotive systems to be able to do advanced diagnosis and troubleshooting, this is the purpose of my channel. I believe any DIY that invests time to study can do advanced diagnosis as good as a professional. It's all a matter of spending time to understand some fundamentals and of course developing the scientific thought process. Good for you bro!
Schrodingers Box 2002 hyundai santafe 2.7 trouble code p1167 , b2s1 and maf were replaced but fault code still found. o2b2s1 is stuck rich even in closed loop the same time stft runing lean around 24 , it is strange lean stft and rich o2 sensor signal. any comment?
My truck is doing this. Bank 1 HEGO reads lean at idle (sticks around 0.30V), and being a V8, I can compare bank 1 to bank 2. Bank 2 switches at idle, rich/lean. If it were a vacuum leak, both banks would read lean. Under heavy load, both sensors read ~0.90V. Interestingly, my scanner said "closed loop, operating on one oxygen sensor due to system fault). Awfully intelligent PCM for a 96' (first year of EEC-V & OBD-II). This is with long tube headers. They didn't fit well, and I had to modify a primary tube to clear the starter. Well, my welding wasn't too great, so a leak is probable...first time using flux core stainless wire did not go well.
Yes the phenomenon you see is a "OL3" where it is a special open loop that disregards an O2 sensor that is not giving proper function. a misfirer will also cause an OL3 condition. I would transpose O2 sensors on B1 and B2 and if the lean condition moves, your diagnosis would be 100% - O2 sensor bad.
I was thinking that the main difference between vacuum/exhaust leaks would be whether the fuel trims make the situation better or worse. Could you reset the trims to zero, and then start the car cold in open loop? I would imagine that if your car starts out rough with 0% fuel trim, and smooths out as the trims start to increase in closed loop, you're probably looking at a vacuum leak. If your car starts smoothly with 0% trim, and only has a rough idle in closed loop, you're probably looking at an exhaust issue. Sorry, kind of new to all of this, and I know it's an old video.
I have P0174 code now and I suspect that it is due to an exhaust leak. This is clearly not a problem of the mass air flow sensor, not a leak in the intake manifold hoses because they would also cause P0171 at the same time. I have been driving fast in bad gravel roads for two weeks and heard occasionally loud noise of rocks hitting the underneath of the car. Also, as you have said, I can clearly hear abnormal exhaust pipe noise.
@@SchrodingersBox I don't even need that. I already found the leak. I can hear and feel the hot air coming out of the leaky pipe section before the converter on bank 2.
@@SchrodingersBox Just to let you know. I'm new in this, 1st time using an obd tool and trying to solve a problem. I appreciate your prompt response and comments. I respect a lot your opinion s. I replaced that section of the exhaust that contains the flex pipe and erased the p0174 code. So far, I have not got a chance to drive the car a lot. 2 sensors EVAP and O2S22 remain not ready. But the fuel trims are now around -15% which seems to have resolved the lean problem. This is a 2002 Toyota highlander.
For wideband O2 sensor the reading is made in the current flow, not voltage. I think I am not wrong, but I learned this on the internet so we never know.
Hahaha you are no wrong at all. it is absolutely read off current flow. the voltage strictly for reference only. it isn’t actually real voltage. I have a video on this in fact.
Wouldn’t the exhaust gas push out the leak and not let air in and the sensor reads the same because the mixture is the same there is just less exhaust as a whole. It would just think it’s a smaller motor by barely?
Okay so what you are saying is that if you have a large enough exhaust leak, it can act like a Vacuum leak, and there is no way to differentiate between the two other than you would hear smell and definitely be able to tell there is an exhaust leak before the O2 Sensor. I have done a smoke test, I have done carb cleaner test, I have done a water test, and I have tried pulling off vacuum lines to try to find the problem and putting them back on to check for engine changes in Fuel trims and RPM, Sound etc. I pulled everything off of my manifold and plugged all of the vacuum lines completely and it still is idling rough, but once I throttle it up it runs perfectly. I am experiencing symptoms of a vacuum leak. However the other day I did notice that on the passenger side I am smelling exhaust when I rev on the engine. Your videos are helping. I am going to check the bolts on the export manifold on the passenger side and see if maybe they may have come loose. My codes are also Po172 and PO174 System too lean Bank 1 Bank 2, LTFT are both at 25% STFT fluctuate, but on Freeze frame I see 3% STFT Bank 1, 5%STFT Bank 2, Code was thrown at 880RPM 20%TP, MAF 0.03, B1S1 .323, B2S1 .788 B1S2 Steady after cat doesn't matter because it has no fuel trim. I am seeing the voltage on the side I suspect the leak is on is lower by quite a bit. that would be Bank 1 Sensor 1, I suspect a rather large Exhaust leak on the side with Cylinder 1, since it is a Ford 460 7.5 Liter V8 That would be the passenger side. That is where I smelled Exhaust wafting up when I coddled the Throttle the other day. Thank you for providing a few Ideas for me here. And the learning experience. More of a Reconfirmation for me. (Note my Freeze Frame Data is going from non specific Memory on the Short term Fuel Trims and the O2 Sensor Voltages, so it may not be accurate: Most likely not!!)
1) is your LTFT also maxed out? 2) how does Bank 1 compare? 3) do you smell unburned fuel at the tailpipe? (watch out for your CAT! 4) is this the new O2 sensor that shows rich?
I have an in-line 4 that falls on its face at about 3000 rpm and even back fires. idles OK. after a few seconds in this condition back to idle at 1700 rpm the STFT goes -17 to -25 . The LTFT never changes at .8. I am lost at this point. help!
@@charlesgould8436 I'd be much more suspicious of a blocked exhaust - I've seen it with plugged cats, and bent tail-pipes. In the winter I'ved seen it with condensation frozen in low portion of exhaust.
Should’ve made it leak from the manifold flange I think I’m dealing with this rn on my 06 mustang gt I straight piped it the manifold studs broke I did not drill them out completely center and didn’t have a Dremel with carbide bits to get the remainder of the bolt out to make it fit as it should and it didn’t completely seat and with my car supposed to be loud going at it by listening to it is gonna do nothing my car is also cammed and I think with it chopping at idle it’s helping air get into the exhaust bc it’s not a steady stream of exhaust and there is definitely a big manifold leak bc I can smell exhaust gasses through my heat at idle when I’m stopped so maybe you can do it again this way?
Maybe, just maybe the difference between a vacuum leak and a exhaust leak would be that long term fuel trim. Maybe try a vacuum leak and see if that LTFT goes up and doesn't with a exhaust leak? I kind of went over it in my head and I don't know if you tried that or not but I wanted to through in my input just in case. It's always great to here other people's input.... sometimes.. haha!
Vacuum leak diagnostics IS our established baseline, rememeber. We are using the established diagnostic for vacuum leak as our control. This would be high FT at idle that correct under load.
Schrodingers Box Here is one for you, a 2010 Kia with no MAF and no EGR Valve. I haven't found out why or any research about it, but I was wondering if you knew anything about it?
No MAF is very common. The engine design is known as "speed density". It uses MAP only, no MAF. Also many cars do not use EGR. I don't know the specifics exactly on how they "get away" with that though- maybe some modification to the catalyst system?
Schrodingers Box I have seen some Civic with no MAF and no intake snorkel lol but never no EGR, it surprised me when I hooked up my Bluetooth scanner and saw no supported PID for MAF and EGR. I'll definitely have to do some more research on that. But you have inspired me to do "charitable mechanic work" for people with low income or people in need. So I do have to say thank you for that!
I would think with an exhaust leak that the short term fuel trim would gradually go positive until a CEL was lit if the car was left at idle for a long period? My thinking is that since the computer cannot make any adjustments to change the fact that the O2 sensor is picking up additional air, it would continue slowly increasing the fuel trims until it maxed out assuming the fuel doesn't foul up the sensor or snuff out the oxygen. Once again at idle with no load. My honda right now i am pretty sure has an exhaust manifold leak. WOT and the fuel trims are perfect zero and driving down the road the car is fine... But as soon as you idle it it will slowly over the course of maybe 10 minutes hit +10% STFT. With the backpressure if i get it negative it smooths out its idle.
I wonder if creating the exhaust leak further upstream of the O2 sensor (for example, perhaps at the exhaust manifold/engine interface), would allow for more time for the air to mix before it reaches the O2 sensor and then cause a "clearer" lean condition in the data streams.
yeah there is also a possibility that a leak at the manifold could increase “scavenging” effect and draw more O2 in than it would further downstream. I have been meaning to test that.
Do you think that the sensor you loosened might not have captured enough oxygen that you could have seen it on the scanner, due to the length of the sensor and the exhaust moving the oxygen past the sensor and missing the sensor area of detection. if this makes any sense. I think, not know, if you had a leak further upstream the sensor detection area might have picked up a little better, the amount of oxygen caused by the leak. Your vedios are the best, and I watch then over and over again and thanks to you, I am? learning. thank you.
The exhaust leak does not HAVE to be upstream of the sensor to effect the fuel trims - depending on the exhaust design reversion can cause the sensor to read lean 8 or 10 inches upstream from the leak - - - particularly at low engine speeds with relaively high overlap. Restricting the exhaust at idle to cancel out the reversion effects (negative pulse) should force the STFT down at idle if the lean code is caused by exhaust leak. (shove a potato up the exhaust with a 1/2" hole in it with the engine idling)
Yea, I was wondering what Matt was trying to do here as well. Unless you're expecting some sort of venturi effect creating a vacuum to be in place why would gas coming out under pressure cause oxygen to get into the system. Completely different deal than a vacuum leak. As an electronics engineer I put everything into electrical terms in my head. With a vacuum leak you have electro-motive force in the direction of oxygen getting into the manifold, here the EMF as it were, is pushing the gas out. With the gas coming out how does the oxygen get in? I know of several cars that have diverter valves in their exhaust systems that switch from wide open headers. (race trim as it's called) to cat systems and mufflers (to satisfy "The Man"). When they hit the switch I don't think their check engine lights come on. They do get louder and have more power with the valve open (or so I've been told since I, as a law abiding citizen, would never do such a thing). The fluid dynamics just seem wrong to me for exhaust leaks to affect fuel trims.
Precisely SATAMAN. The experiment was designed to allow for the possibility of Venturi effect, and I show it does not exist in an exhaust leak. Now, that said- what I showed is it does not exist AT THAT LOCATION, and that is correct. I did not think the location mattered. What some people are saying now is there is a dramatic difference if the exhaust leak is between the exhaust manifold and the head. In that event, supposedly, "scavenging" of the exhaust will suck in outside air similar to a vacuum leak. I will need to repeat this test with an exhaust manifold leak to see if their theory is correct and increasing RPM would actually cause more of a lean condition instead of improving it.
DE Nichols No sir, you did not, when the rear O2 wetn more positive, like this Air Fuel ratio going more negative since it's opposite, I was having no venturi effect. I have now unwritten invalid memory in my head.
DE Nichols I think this is final data, and I may need help understanding it. When I had almost sealed the pre-catalytic converter leak, post bank 1 sensor 1 O2 sensor, the downriver O2 sensor no longer reported rich unless there was a lot of rich driving. When there was a leak it'd go rich regularly. I believe the exhaust was only escaping. When it would escape worse the downriver O2 read more rich...that makes more sense to me if it's pulling air in, so I'm officially lost as to why that O2 sensor read more rich.
In the unlikely event that there are 0 codes but your fuel trims are shooting from anywhere from -7.8 to positive 28 with low voltage to the post cat sensors what would that be exactly?
I'm curious to see what would happen adding a little bit of propane to brake booster and see how that changes things. I would bet an air leak cause by exhaust leak would be more visible because it's closer to o2 Just a thought
Hello too the channel I was looking at all the videos and the one ting that I was told if your going too use a aftermarket or reman maf it could make your life go crazy. Plz use oem maf from the dealer 😔😔😔 I hope you look at the Maf again because it the hold all the spac
I came in just hoping you could differentiate an exhaust leak vs vacuum leak just with the scantool, have you since found a way yet? I'm tracing a slight lean condition, and the signs are pointing to one of these. Does a vacuum leak always result in a higher rpm at idle? Wouldn't the ECU compensate, and keep the idle speed normal?
Interesting, but I think we need a lesson on venturi effects. That blue BMW R100Rs motorcycle (pictured) has venturi air injection to burn off hydrocarbons in the exhaust system. It is an intentional air leak into the header pipes, and the air is drawn in by a purposely engineered venturi just downstrean of the exhaust valve. Exhaust system pressure has to be greater than atmospheric pressure for exhaust gas flow out of the engine. So the question is...... is the average exhaust leak going to act as a venturi and suck in air, or act just like a leak and let out only exhaust? If the leak is acting like a venturi, then leanness might be detected. If the leak is just a leak, then the sensors won't detect any change.
You must be testing us to see if we are paying attention. At about the 8:44 minute mark the color codes are right but the labeling of the lines is reversed.
Ah yes, I only pay attention to the color coding so I didn't really notice the locations where I put the labels. The location of the labels in the legend is not meant to be significant, only the color is, but I can see now how that might be confusing. I will consider that next time.
The issue I have with this reasoning is that is there a positive pressure or negative pressure where the exhaust is assumed to have the leak? O2 entering would be possible if the pressure there is less than the outside pressure. I am guessing that is NOT the case. So please *now* explain how you are getting extra O2 to be read by the A/F sensor under the condition. Did I miss the baseline readings where you looked at the waveform with NO LEAK? Do you not see pretty similar AFR vs RPM graph with OR without the exhaust leak? My apologies if you showed that experiment and if indeed the graphs were drastically different.
12vgs8606 Yes I see your points and I can address them First off and most important, you did miss where I did the control validating the waveforms with no leak- it is the single most important baseline to do and had I not done that, I should quit doing videos! You may have missed in my explanation of the A/F and equivalence ratio data outputs. And of course, the non-leak control showed normal response. For the positive pressure- there is absolutely positive pressure in an exhaust- evidenced by the facts that you "feel" an exhaust leak with the puffs through the leak as opposed to a vacuum and also by the fact that I was unable to do any WOT testing because the loose O2 sensor kept blowing out of the hole. This is why I had to generate such a surpringly large leak to get O2 in the system. By just having the sensor threaded very loose, no leak was detectable. Presumably, air might also be forced into the exhaust leak when the car is moving I suppose.
I am still missing your baseline test where you increased the rpm and watch AFR. You did the snap throttle test but did not do the steady increased rpm test. Come to think of it, you did not have RPM as one of the parameter being monitored on the scanner but it was on your whiteboard! If there is positive pressure, why are you then showing air entering (aka extra O2) through the hole? Bottomline:- we both agree that undetected i.e. minor leaks in the exhaust does not seem to have much effect on drive-ability or the fuel trims.
12vgs8606 Wow you know what... in editing I clearly must have accidentally eliminated the reving baselines that I did. Shoooooot. My bad! But I did do them and they were fine. Fantastic catch. Damn now I got to pay more attention while editing as I do filming and fixing!
At least I was not going crazy! So, without the leak, O2 and FT remained flat plotted against RPM? That alone would be a good diagnostic tool! For some reason, I was under impression that there is no such thing as "the" fuel trim but rather a multi-dimenional array of fuel trims or "cells" of fuel trim data based upon key engine parameters such as RPM and/or load. If that is the case, chances are fuel trim may not be constant against the RPM even in ideal cases where there is no leak.
12vgs8606 You are correct- fuel trim is done in "blocks" but since I did reset the fuel learn or disconnect battery or anything, the test I did is valid both for control and variable.
Is there any way an exhaust leak would only affect bank 1? My LTFT and STFT is at 25% at idle, but when RPM increases the STFT rapidly decrease eventually (actually pretty quick) reaching -15%. LTFT will slowly drop usually to 12%. My truck will start running better and stop misfiring at these fuel trims. The check engine light use to blink for cylinder 2 misfire but now I get no code, although, I feel the misfire at idle. A vacuum leak or intake manifold leak is the only issue that makes sense to me so far. Can it be anything else?
@5:27 "...but don't worry, I'll explain whether the procedure worked or not - if you're too lazy to go look at that..." LMAO You have such faith in your viewership. lol
i have a lean condition only at idle,i have a wideband o2 and guage that exposed the lean condition,further investigation i found major leak between turbo and manifold right before the factory o2 sensor.i can feel the exhaust leak with my hand,my question is how does the leak suck in air to cause the lean mix is it valve position or overlap or venturi effect? im trying to understand why ths happens,thanks.
Venturi effect. Most people think that there is a constant “outward” pressure from exhaust but remember it happens in “pulses” and even then it is a really low pressure - far, far under a PSI. The oxygen can be drawn in and in fact I have a video somewhere proving as much.
@@SchrodingersBox thank you for your response one more question for you,on a turbocharged motor can exhaust leak cause rich at wot in full boost? i had to order new exahust manifold gasket for my lean idle but all a sudden im having a rich condition under full boost with the lean idle,with the exhaust manifold pressurised is this pressure leak in exhaust causing the new rich condition at full boost? whats your thoughts? ps my afr at full boost days ago was around 11:2.1 ,now its 10.0. so not sure if the o2 could even add this much fuel?
update: checked codes and found knock sensor code.i beleive the lean idle caused some idle knock which threw this code,im thinking this code may be pulling timing and adding fuel under boost as protection does this sound like the correct theory?
It sounds like “a” correct theory but not “the” correct theory. It would be “the” correct theory of you could see ignition timing correction from the knock sensor.
Man I wish you were located in Chicago. I have taken my car to about 4 shops and no one can figure out my p0171 code. I have a 2005 Honda S2000. It has rough/stumbling engine at idle. I’ve done the following - fuel pump, injectors, fpr, pcv, iat, map, valve adjustment, o2 sensor, checked for vacuum leaks, brake booster, iacv, replaces intake manifold gasket, checked for exhaust leaks, and tried a different ecu. Compression is all within 215-230 what else can I try? Can it be a burnt valve or slightly bent valve? My car drives fine but my fuel trims stay really lean 15%- 30% thank you and I hope to hear back!
What data do you have? You say the MAP was changed- what was the MAP data that indicates it was faulty? Intake gasket was replaced- what was the fuel trim data indicating it was faulty? Fuel pump was replaced- what was the amperage under load that indicated it was faulty? You have to give the data you are using for all this.
Schrodingers Box hey thank you for replying! Unfortunately I didn’t come across your great videos until recently. The parts mentioned were replaced without actually gathering data like I should have. I’ve been watching a ton of your videos. I’m still learning a lot. I just made a video and posted it on here so that maybe you can see what I’m looking at easier. It really hard to explain it all and I know it’s hard for u to tell me without actually having the vehicle. Let me know what I can record to maybe have you better help or give me advice on. Here’s the link to the video I made. Sorry I’ll try and get an actual video of the data from driving around. czcams.com/video/nuEBYdy1gyk/video.html
The FIRST thing you need to do is a cyl leakage test. This will detect ANY valve issues. Next is a "dynamic compression test" or "power balance test" - basically dissable one injector at a time and compare the rpm drop with a sensitive tachometer. This will point to which cyl has an issue (valod even without leakage test - but will not pinpoint the CAUSE of the inbalance - which the leakage test WILL if it is "mechanical". (In the old days you did this by shorting the plugs one at a time - but that can harm catylitic converters)
Absolutely it could. Right now we can rule it down to anything which determines idle control, fuel ratio normalization, load detection and response, or even mechanical. Which means everything. See my response below.
@@SchrodingersBox i can hear ticking noise from passanger side head and unburned fuel on exhaust manifold or inside ex manifold. U can check my channel last vid
On my 4.3 vortec engine (at idle & in closed loop) I have LTFT readings of about 12.4 (both banks) & a post cat O2 reading of 0.08. The LTFT goes down and the O2 readings go up (but not by alot). I going to pull the O2 sensor and test it but if this is an exhaust manifold leak would introducing propane to the exhaust manifold bring up my O2 reading and improve fuel trim, or is there anything else I can try short of pulling off the manifolds to inspect the gaskets? Any suggestions would be appreciated.
lean condition. exhaust leak or intake leak(or filter mounted directly on a maf sensor! . definitely causes your car to compensate. (test it you Wil see.
i’m having a p0171 system lean bank 1. i do have a pretty substantial manifold leak and a exhaust flange leak ( can hear it very clearly) my fuel trims at idle are 25%. obv the leak is before the upstream 02, could this cause my “lean” condition? chevy 6.0 vortec
so under load it’s dropping down to a 11-18% would that be a fuel pump issue then? or clogged injectors? i just ran some sea foam through it and that seemed to make it even worse than it was before
Looks like a leak to me. You have to fix all exhaust and intake leaks before a fuel trim analysis can be conclusive. What was the seafoam supposed to do? I don’t see how that is going to correct a fuel trim anomaly under load.
originally this all started bc i was noticing my fuel consumption was abnormal. yes ik a 6.0 is a gas hog but im talking maybe 8-9mpg highway and down to 5mpg climbing hills. i thought the injectors were out of whack so thats why i bought the sea foam to try and clear them out.
If your sensor is cross threaded like mine was it will leak alot and throw codes. Mi e threw po420. I couldn't hear it untill I crawled under the car and had someone rev it!
Not possible. How did it cause superimposition of the signal from just a leak? Impossible. Did you also verify AFTER that the leak didn't damage the cat and cause loss of activity? Did you validate actual catalyst activity? I have yet to ever someone who has.
Schrodingers Box Mechanic said that if the leak is near the sensor, O2 could be introduced into the stream, or exhaust gas could rise into the engine compartment altering the reference air.
@@alalan3735 it has to be upstream of the sensor in order for the sensor to read it. If the oxygen is introduced into the exhaust system downstream of the sensor, it will never cross over the sensor, so the sensor will not be able to read it.
Well it will fix the P0174 if it fixes the leak. Or just replace the gasket if that’s all it is. Last ford truck I worked on with an exhaust tick, it had a broken manifold bolt nearest the firewall.
Hello, Do you think an open exhaust valve would cause the same pattern? I'm curious because my car has a high LTFT that is not from the vacuum leaks or an exhaust leaks.
+Schrodingers Box Sorry for late response. Somehow youtube messages show up in my email box late. Of course, compression test how did I miss that. Thank you for the reminder. And nope the exhaust valves are not the problem, compression are within spec. all six are around 190 psi +/- 5. So I guess back to more diagnostic.
removed battery to be able to have more room rereplace a headlamp, then engine light came On, had it checked then this is the code (0P106),Replaced it!!, then it worked for 3 days.(engine light still on) returned part thinking it's bad, put the original part back on ,(engine light still on) finally took it in to a dearlership service dept. they tell me I need to replace the ECU/ENGINE COMPUTER! but before that I had a personal mechanic look at it and he said there is a engine leak! This Corporation just "put out" a 2nd revise RECALL on Engine replacement BECAUSE of a Engine block issue I am a Woman, and that may mean to some; tell me anything! But I don't like dishonesty it can be dangerous and most certainly wasteful TIME /MONEY!...YOUR VIDEOS WERE VERY HELPFUL UNDERSTANDING (wish I could take YOU with me to that service dept! ) I have no desire to spend $1200!!!! when It seems like the computer is working enough to give off code P0106!!!!! Any Positive suggestions are Welcomed not sure what to do next after I go pick it up!
I have engine 2tr no dtc with lean conditon with 88⁰c temp heating engine a while b1s1 at 14-23% and b2s2 at 0% at idle and i notice that the s2 doesn't folow to +.. put some rpm at 2500 it still the same trim no change at all. What could be the cause thanku
@@SchrodingersBox yes b1s2 doesnt react on 700rpm and 2500rpm At idle Stft 20% flactuatng 14% Ltft 0% Rpm. 800 Temp 88⁰c Pedal is on hold Stft. 20%. Also flactuatng 14 Ltft. O% Rpm. 2500 Temp 88⁰c There is high fuel consumption And trying to a fix . black smoke comming out the pipe is present at sudden acceleration
No- the O2 is reporting the issue, not causing it. You don’t have enough data to identify a cause. You need to show an actual load curve of LTFT and STFT against RPM.
@@SchrodingersBox I cannot figure out what is going on when I remove the af1 the result was nearly better.. I have reading at b1s2 at 9% and b1s1 at 0% and check engine light was there. No vaccum leaks change plugs IGN coils injectors cat coolant temp sensor MAF need further diagnosis of which I don't have. It's maybe a bad ecm Ive done it all changing outputs and inputs but still no changes.
Well, just to be different, I'm going to address other areas that could introduce vacuum leaks with positive intake vacuum. I really haven't a chance to study up on the LS1 configuration. But, I'm brainstorming things that come 'on' during positive pressure... I know of purge valves and EGR valves opening during positive manifold vacuum. So, I would completely replace the EGR system and purge system and perform tests again. Just kidding. Thought you'd get a kick out of that one. I suggest using a hand pressure pump to test these solenoids, bi-directional communication, and/or smoke to test the valves. In addition, I would also display the appropriate PIDs, e.g. MAP, purge solenoid status, and other emission related devices, and snap the throttle to see if I noticed any correlations. Just for kicks, I would hook up a vacuum gauge and ensure the needle is solid at all RPMs and at the appropriate values. Now, I'm sure your response will be that these systems would affect the manifold completely. I agree with that, but I don't know the LS1 configuration, meaning perhaps these systems are hooked up to one side. I tried to listen during the video and didn't hear any hissing. I thought I heard a little off throttle hesitation. I'm sure I'm going to be totally wrong, but I would think an exhaust leak would affect the FT values at all RPM ranges. I would think we would hear the leak at any RPM, some more than others, on such a big displacement motor. Lastly, thanks for sharing this experience with all of us. This way we all learn.
***** Man I will admit, you totally got me on the "replace the whole EGR system" lol- I almost threw up- really. I need to revisit this video anyway since new evidence suggests the location of the leak may be a variable- a leak at the exhaust manifold itself would supposedly result in "scavenging" the outside air and creating more of a lean fuel trim effect. But whatever the case is- even if that's true- ultimately what I need is a way to differentiate the evidence of an exhaust leak from a vacuum leak using scantool data. I am not opposed to vacuum gauges, etc but I am looking for a scantool methodology specifically. Any ideas on that front?
Schrodingers Box Sorry about you tasting vomit. LOL I didn't intend to take you that far. Just wanted you to laugh. I was going to pretend I put your issue on a forum and indicate they suggested it. But, I knew that might prevent you from reading further in my comment and miss my joke. Well, I have used the MAP PID in graph mode to check out vacuum leaks, but to be honest, I've had better luck with the old school analog vacuum gauge since I wanted to see bounces, inHG, or slow response. Since the ECU, PCM is taking periodical digital samples from the sensor, I feel it just isn't the same. For example, a leaky valve might not be noticeable from a MAP PID but a gauge would show it straight up. Shooting from the hip, I would run the car and use a water bottle and spray around intake and headers to see if I could hear the leak, which is going to be challenging due to your healthy exhaust system. I believe the intake would make a sucking sound, and the exhaust would sound bubble-like. I understand you want to do it via a scantool, but it isn't bad to perform physical tests when the issue could be physical. Right? I can't wait for your next video and what the real issue is.
I plan on using propane and a smoke machine to check for exhaust leaks. No need to check for an intake leak, as that is ruled out by the fuel trim at idle.
***** At about Matt's vomit moment, I was like, okay, please don't let this be real and, with my reaction less severe, I did have a pretty good laugh thank you. ...So, Matt, if my exhaust is leaking, it'd be best if I just replace all of it, right? ;)
i recently purchased a 1999 toyota 4runner and i was convinced the lean condition was from the awful exhaust leak i could hear coming from the manifold. no one believed me. after inspecting this weekend, i realized coming down from the manifold just before the first o2 sensor, it wasn’t bolted properly and there was a gap between the two pipes.
like you mentioned, all the data pointed towards a vacuum leak. at idle, fuel trim was plenty into the positive (higher than your findings here as i literally had a gaping hole), while under load the vehicle’s fuel trim nearly evened out.
that being said, i still thank you for this video. two of the people who suggested it couldn’t be from the exhaust leak are mechanics. they aren’t nearly as familiar with fuel trim and reading data from an OBD scanner as i am, and you have been a huge help as a resource.
i don’t think it’d be possible to differentiate the two (as you found in your video) but it’s important to understand that they have identical traits since they’re both unmetered air that can result in a lean condition. i hardly ever see it brought up as being a possibility with a P0171, and after asking around i’ve realized most people turn down the idea before exploring it.
How long did it take for LTFT to return to normal after the fix?
I am an automotive technology student, working to get my certificate and then become ASE certified. Diagnostics is the best. Im not taking classes over the summer so I get my fix by watching your videos. Thanks for sharing the knowledge.
Thank you for sharing your knowledge here in your videos. I took the newfound knowledge and went to work interpreting my data. LTFT at idle is 14.5%, and S1-O2 at 0.780V. The readings level out at higher RPM's. The exhaust smells at idle as well as having a high NOX value on my smog test - that's what got me looking to figure this out.
So I went searching on the exhaust side of my 1997 Pickup KA24E (Nissan 4 Cyl). What I found was a broken exh. manifold stud. Using propane to find a leak had no result/change. But the broken stud had me concerned, so I disassembled. The lower gaskets of the manifold were on the brink of disintegration. The upper gaskets were fine with no visible leak deposits. The O2 sensor had a white coating of baked on deposits too. Not excessive, but enough to alert me to a possible coolant leak internally (head gasket likely). But here's the interesting part. I cleaned/polished the exh. manifold. Had I not done so, I would have never seen the hairline crack in the Y where 1+2 & 3+4 ports meet at the lower dump.
So with this newfound insight, I reassembled with new gaskets and have to order a new exh. manifold. I know you say not to throw parts at a problem, and it takes a big exhaust leak - which would be audible - in this case my truck isn't loud, but I do smell some exhaust in the engine compartment when I first open the hood. The hairline crack in the manifold warrants a new part, as well as new engine mounts - since there had to be a cause for the broken stud and cracked manifold. So I'll see if the new manifold corrects the high LTFT value at idle.
@Carter Edison New Exhaust gaskets helped. New O2 sensors helped as well. I did discover a hairline crack in the stock cast iron Exhaust manifold. As of this day however (23 years old and 225,000 mi), I am in the re-assembly phase of a completely new engine (Nissan KA24E) rebuild, and in doing so, I see the root cause of all the little issues... a worn out engine. I'd love to replace that mani with a new set of headers but there's this thing with the smog test in CA.
I experienced this condition with exhaust leaks downstream of the pre-cat O2 sensor. Pegged lean at idle but would start to run rich around 2-2500 rpm. After going nuts trying to find vacuum leaks I plugged some exhaust clamp leaks between the cat and muffler. After a test drive reading the o2 sensor and trims, I think that the fixed it. Thank you for the video
I was looking for information on this topic.
I've been banging my head against the wall trying to find an intermittent lean code. I wondered about the significance of an exhaust leak. Your theory is valid. Great job explaining. Thanks man!
Right on the money, I have a ford expedition 2003 with that problem.
P0171, I fix all vacuum leaks and smoke tested (under the hood, gas tank, and exauat pipe) and the code continues P0171 to show. Since Short trim continue to follow long trim however stay a 20 %, at high speed there is not a problem, when you lower around 1100 RPM an OPEN LOOP happens, since the delta between trims goes around 25%. IF continues I fault loop shows and the computer operates in OL. This is confirmed if you follow the Oxigen sensors. Today I went below Expedition to find 3 broken bolta at the exaust manifold at bank one. I watch your video on the 3D adaptative matrix and definitive make sense the computer will take charge to avoid flood the inyectors with gas due to a rigid follow up on the 14.7 to 1 golden rule. To notice is that is that a lower ambient temperatures the engine work smothly and nice, I guess is because the mass of air at mass afected by the IAT. It definitly one hell of diagnosis, Thank You for the videos, I have learn a lot.
How long did it take LTFT to correct after you fixed the Exhaust Manifold?
Exhaust leaks explain themselves well, especially bf the cat. Technicians on the clock, expected to up-sell, and sell as many parts as possible, diagnose things differently. That's why since youtube offering a wide range of perspectives, all are important bc there's always diff details mentioned.
Thank you for your educational videos.
Myself, I love science. Your way of explaining the diagnostic concepts is superb.
I have spent over 2 weeks watching your videos on CZcams and its been great. I have learnt a lot.
My car’s LTFT and STFT have been moving all over the place. For the STFT it goes as low as -22% and as high as +28% at different engine load conditions during driving. After watching some of your videos, I decided to look for vacuum leaks. I found one around the intake manifold gaskets, so I got that fixed.
That stabilized the STFT and LTFT at idle. After sealing the vacuum leak, at Idle, I get between -3% and 0% on the STFT and a constant -1.85% on the LTFT. But when I increase the RPM the STFT moves randomly between -19% and +10% while the LTFT moves only slightly between -4% and -1.85%.
Here are two examples I caught on the scan tool while driving:
1. At RPM of 1253, Air/Fuel ratio (lambda) of 2, STFT at 0% and LTFT at -2.34% (fuel system was in closed loop).
2. At about 2400 RPM, STFT was 0.78%, LTFT was -3.91%, Air/Fuel ratio (Lambda) was 0.98, O2 Sensor (B1S2) Voltage was 0.66 (fuel system was in closed Loop).
I also noticed that the intake manifold pressure is 33kPa at idle. But when I increase and hold the RPM at about 3000, the intake manifold pressure immediately increases to about 47kPa and drops to about 28kPa although the RPM is at 3000. I don’t know if that is normal. The car does not use a MAF sensor.
My car is a 2010 Kia Forte 2.0L 4-cyl engine with 121,776 miles on it. It uses an Wideband O2 sensor upstream and a narrowband O2 sensor downstream. I often feel a hesitation in the engine when I depress the Accelerator pedal.
Can you please suggest what the problem might be or further tests I should run?
not sure what the problem is. what symptoms are you having? everything sounds normal the way you describe it.
Hi Matt
I believe there is a direct correlation between intelligent content and intelligent responses from participatory viewers. I have yet witnessed such intelligent and respectful contributions on other CZcams channels. I think the only way you can learn is to engage as many people as possible. Good for you Matt for providing a unique venue for learning thru you and your viewers. Thanks 😄
Steve Rob That's how we roll! If you like the format and philosophy the channel follows- stayed tuned for "Schrodinger's Mailbox" first episode coming soon!
Matt. Not a wate of time at all, because the conclusion is valuable. If you have an exhaust leak that is causing a lean condition you can more than likely hear it. That is valuable!
Thanks for taking the time . Quite the experiment. All my grief is coming from, bank 2 o2 sensor 2 . Went from a 430 code to lean , low voltage codes. Cat looks good. New o2 sensor stays at 590mv others about 200mv higher. Car seems to run fine I just want it to quit throwing codes.
looks like it’s stuck at bias voltage to me. check your bias voltage and compare to the O2 voltage. also induce a lean condition and see if O2 responds accordingly.
A good physical inspection is always a good place to start. Currently I'm dealing with a similar issue on a 2001 GM 8.1 with high long term fuel trim on bank 2.
A quick visual inspection revealed a leaking manifold to pipe gasket on bank 2.
This leak actually draws air into the exhaust by the venturi effect causing long term fuel trim to advance to plus 20 percent. Diag by verifying and repairing exhaust integrity before any fuel trim diagnosis can continue. Once exhaust integrity is verified retest revealed stable normal long term trim numbers.
If you're customer doesn't want to fix the exhaust leak you can not continue to diag it verify correct operation and your job is done.
So you heard the exhaust leak and checked for a leak at the exhaust? Yeah, I would have done the same. Especially AFTER checking fuel trim and determining there is an unmetered air leak on only one side of the vehicle. Of course its a place to look.
Now if you did a visual inspection without knowing the fuel trim analytics and found that- I'd be impressed!
Subscribed as soon as he said "asshat's garage",
His humor and knowledge got me subbed
Sorry I should have also said great content and thanks! Stuff like this is how I built my first 302 from the ground up, only using youtube and a couple of great friends. This kind of content is sooo underrated. Thanks! 👍
Very helpful video. Prior to viewing this video I never thought an exhaust leak would behave like a vacuum leak on fuel trims - creates a lean condition at low rpms.
Good news for me because it is now less likely that I have an exhaust manifold leak since my scan tool reports a lean fuel trim condition at high rpms and a neutral fuel trim condition at idle. I have two banks and one has twice the change of the other so it is not a fuel pump issue.
Now to turn my attention to lazy fuel injectors.
having exhaust gas leaking around an O2 sensor will cause it to misread. Remember, an O2 sensor must sample the oxygen level of the ambient air (without dilution from an exhaust leak at the sensor) to work correctly. My understanding is the same principle applies for both wide and narrow band zirconia sensors. I believe you would need to induce a leak well away from the sensor to make this a true 'scientific' test. Your videos are very informative. You're diagnostic skills are first class. Cheers.
I'd also be interested in seeing this experiment be re-done with your suggestion.
Hi, I've been doing similar testing. I found that partly blocking the exhaust can be seen on the O2 sensor reading and STFT, if they have been altered because of an exhaust leak. I believe the theory behind this is that as the exhaust does in effect pull oxygen inside when a "negative pressure" wave caused by air mass is induced inside. This will not happen if the pressure inside the exhaust is greater than that of the surrounding air. The blockage shouldn't be too large or be kept for long though, as It will slow the speed of the exhaust and cause problems with exhaust gases leaving the cylinder.
That is really smart and would probably be the distinction between an exhaust leak and a vacuum leak. You sir, deserve a cookie for that!
Spent two months trying to find why my foxbody was surging/fouling out plugs. Turns out the slip tube on my new long tube headers had a massive leak. No CEL at all but ended up getting a passenger side lean code during KOER test. Created a vac leak and bam confirmed diagnosis.
Der Matt
First: Great Channel
After watching all Your Videos and learning a lot I have a problem concerning exhaust leaks. As an engineer by training and an Airline pilot by trade, Physics dictate that an exhaust can only leak from the inside out. There is always a higher pressure inside the pipe than on the outside, else an exhaust would suck air into the tailpipe. Now for Your experiment,You had to take the O2 sensor more or less out to get a lean condition. At this point You are exposing the sensor to the oxygen rich outside air and hence the lean condition starts to happen. To eliminate the possibility of a mistake on my part, I drilled a hole into an exhaust (junk car, but engine still running) and airflow happens alway to the outside only.
Everything else on Your channel is great and has improved my troubleshooting and understanding a lot. Also I have resolved the P0105 on my wifes Jaguar, and it sure was not the MAP but a serious carbon deposit in the throttle body bringing the TPS out of idle limit. Great, great, great since they would have NEVER found it at the shop.
Keep up the good work and if You want, You can reach me via email,
bernhardlist@hotmail.com
sincerely, Bernhard
Bernhard List Pretty good analysis however a couple things:
While the pressure in the exhaust is higher, I think you are not accounting for the theory of vacuum by the Venturi effect (Ironic, seeing as how you are an engineer and pilot since Bernoulli principle is involved in that). This in fact accounts for the reason you do not have vacuum at the end the tail pipe (which you are correct about, but Venturi effect no longer applies at the end of a stream) but would theoretically have it along the tailpipe. What people are claiming is venturi effect causing vacuum of outside air. Exhaust "Scavenging" is another example of this for those into high performance applications. So I think you overlooked these physical concepts/laws in your analysis.
Second, your experiment did not describe how you eliminated that possibility that there was venturi effect.
And third, just in a grammatical sense- the sentence "As an engineer and pilot... physics dictates" indicates that the laws of physics are dependent upon your education and career choice. "As an engineer and pilot, my understanding of the laws of physics would indicate" would be proper poisitioning.
Bernhard, I've got a P0105 on a 2004 Jaguar s-type 4.2, and was curious where your carbon build up was and how you cleaned it. On these vehicles i saw somewhere the MAP is really just monitoring the EGR, which i thought might be clogged with build up. Thx much.
I've been fighting with an exhaust leak because I thought it was the cause I'm very glad about your findings because this thing is impossible to drill the bolts out of the manifold and I don't even hear it.
Just to be sure I would inject some propane around the suspected leak and check response from O2.
2003 Mach 1 Mustang, took it to a Pro Exhaust shop to have a SLP X-pipe installed. Instructions said to remove drivers side manifold studs and use bolts which they did not do. Drove around for a year with an exhaust leak. Could smell fumes and it finally threw a P0174 code (lean, bank 2). Fuel trims were way outta whack for bank 2 which triggered the service engine soon light. Took it back to the exhaust shop and they made a shim vs removing studs. A few days later got a P0171 (lean, bank 1) because they loosened passengers side to fix drivers side. Mechanic said if code came back to purchase a Ford manifold flange gasket.
your scientific approach brings automechanics for another level of wisdom:)
Or maybe to their first one in most cases lol!!
Great video as always! So basically if there no abnormal exhaust noise, the lean condition is something else. I have a Corolla that is leaning STFT is about 8% LTFT 14.2% with some bad fumes around the car and with the heater running so someone online told me to check for exhaust leaks despite the fact that i don't hear any abnormal exhaust sound.
Yes, exactly! My findings show that you have to have a significant leak to get the false lean response.
I would recommend curving your fuel trim against load to better narrow down the cause.
@@SchrodingersBox Will do. Thank you for your work.
Loose exhaust manifold and/or Loose catalytic converter... do vacuum and soapy water test... Tighten the bolts if confirmed.
Madd genius . Helped me with my flange leaking. Yes i needed a exhuast gasket
Okay, so you may not have created a new test, but the information was new to me. Whenever I see fuel trims that say intake leak, I should listen/feel for an exhaust leak. That had value to me. The doubter in me is going to feel for an exhaust leak until I see it for myself. I realize that your test showed the leak would have to be very significant and therefore it would be heard.
Upstream of a cat, I've seen exhaust leaks change data a GREAT deal, even on small leaks, so it's effect on a P0420/430 may be more significantly definitive by sensor data alone than a pre-upsteam fuel/air ratio sensor.
A caveat occurred to me when I woke up in the morning, that an O2 sensor may more easily react to a leak at the same spot than an air/fuel ratio. Since the Air/Fuel ratio supposedly actually sees the ratio of air to fuel, that ratios could be the same whether it's leaking or not.
Perhaps, the difference for an O2 sensor reading a much smaller range would be more sensitive.
The other analogy that occurs to me, is that the exhaust escaping over the Air/fuel ratio sensor, the escaping exhaust may be acting like shielding gas on a weld. It still wasn't seeing much atmosphere because it was getting covered by the leak.
Leaks elsewhere can still be theorized on how they'll look based on this fine experiment. This does suggest that this leak may have had to be bigger to see the effect.
DE Nichols nn
Sure you can, it's simple. A quick check I like is to watch fuel trims/O2 activity at
idle and have a helper stop up the exhaust then see if trims/activity change. I see this on vehicles with broken bolts at the manifold. If you stop it up you create positive pressure in the exhaust system. This prevents any air from getting sucked in
through a leak. If you take away that air, then the trims should shift downwards. One thing to remember on your smoke test from the rear. You'll never get enough smoke through the cat to ever see it. so anytime your actually looking for a leak, pull the front o2 and smoke it there, or if it's a ford, pull the rear DPFE hose off and smoke it there. Remember, you can barely see daylight through a good cat.
Sorry to differ but you're dead wrong about the smoke test. I have detected EGR valve leaks, manifold leaks and in fact AIR leaks with smoke to exhaust pipe- as have dozens if not hundreds of my viewers. In fact it is amazing how quickly the system fills.
As for the blocking the exhaust, that's a great idea however I will need to try it with a negative control by blocking the exhaust without an exhaust leak to make sure full trims dont shift downwards just from the blockage.
Schrodingers Box
Ahhh, when have I ever let you down. I have 2 of the same smoke machines you have. Put yers on a late model F150 and then get back to me on how "quick" you get smoke up to the DPFE sensor :o)
Great experiment. Good to know. Thanks for sharing. Always a good time hanging out.
You wouldn’t hear the leak on the turbo to downpipe exhaust gasket on for example…a European “hot v” engine such as the ones made by BMW and Mercedes yet this Will perfectly produce the fuel trims that you were trying to achieve.
"For a second there, I sounded like Scotty Kilmer, except what I said is actually useful." LOL!!!!!
Damn! That Scotty Kilmer roast though! Yup, that's it, you got me to subscribe to you. But you're right, what you say is actually useful lol.
I’m suspecting an exhaust leak (can’t find any intake leaks) on my Nissan 3.5. What throws me off is the car basically fixes its fuel trims during a cold start up and initial warm up, as well as highway driving.
The problem is most detectable during long, hot idle. That’s when the STFTs jump upwards of 10-15% on both banks, on top of the already high LTFTs (10% and slowly going up as the car keeps idling).
I haven’t tried leak testing the exhaust yet.
I agree with your findings that with an exhaust leak at the sensor, or for that matter a leak at an exhaust pipe/header flange connection, there would be minimal effect on fuel trim. However, an exhaust leak at the exhaust manifold (with either a crack or a leaking exhaust manifold gasket) near the cylinder head there will be a different result due to the proximity of the individual pulsations caused by exhaust from each cylinder. As the cylinders are exhausting, particularly the ones on an exhaust manifold that are downstream of a crack, they will induce a vacuum to draw in oxygen at the crack.
johnwrench4speed Hmmmm, I will have to test that- but no way I'm doing that on my cars lol. And not because I want to induce a leak, but more because the manifold is not accessible on either without much dismantling. If I ever get a chance, I will induce a exhaust leak at the manifold on a car if I get a car where the manifold is easily accessible.
A little wordy with description but it was what I have going on my car . Thanks for the knowledge.
+Schrodinger
A few ramblings...
The STFT increases when the "exhaust leak" is induced. The rising A/F signal causes the PCM to *BELIEVE* that the engine is running lean when in fact it is running rich due to STFT correction. This should generate some additional activity (heat) in the CAT due to the additional fuel. This heat increase may not happen to as great a degree if you were to induce an intake vacuum leak. In that case the engine *REALLY IS* running lean and the STFT is bringing the engine back into stoichiometric balance. At stoichiometric, the CAT might be less active (cooler?).
This observation is only useful as an exercise in the case where we know there are initially no leaks and we induce one to watch the changes (i.e. the CAT heating up). It is still not helpful in differentially diagnosing whether an engine of unknown initial state has an exhaust leak.
I agree with you that an exhaust leak will be heard long before it becomes serious enough to affect fuel trims.
I still wouldnt rule it out an exhaust leak even if you cant hear or smell it. I had a leak on both banks (2013 Taurus), which couldnt be heard(or smelled? Idk my nose is shit). It improved fuel trims by about 10% but LTFT is still high at 16%. So I may have both exhaust and intake leaks.. I will find out soon.
I appreciate your feed back.I will put a map sensore in and hope for the best.If this don't work what should I look for next.
If you just change the MAP sensor and hope for the best, it won't matter what you look for next. If you are just going to just guess at parts without diagnosing if they are faulty then there is absolutely no reason to try to put a methodological systematic strategy to it- because it's impossible. Just guess and swap on a whim.
But I'm not sure what you are doing on my channel if that will be your decision after I made 78 videos showing conclusively how that is the wrong strategy. Nonetheless if that's your approach, I guess one strategy might be to post your symptoms on any automotive forum- you will get more ideas on what to swap than you will be able to afford.
And as long as your hoping for the best- instead I would hope it isn't a vacuum leak- because no parts changing will fix that. Of course even that is illogical- hoping that something is not an etiology has no effect on whether it actually is or not.
I am going to take truck to have a nother complete diagnostic test tomorrow.I assumed a diagnostic was to pin point the problem or steer a person in the right direction.your right I'm not going to keep guessing.
check engine light on. Wish it was a different code or even a 2nd code with this one. Got a P0171 code (lean air in bank 1) parts that have been replaced within the last few years or within the last few days.... EVERYTHING YOU COULD THINK OF!! cold air intake hose, spark plugs (#3 had oil on top of the spark plug and boot - spark plugs replaced- boot cleaned off - access oil inside clean up.) Had to replace the valve gasket? Pretty sure that's what it's called. No air leaks. Both 02 sensors replaced. Maf sensor replaced. We are waiting on an exhaust manifold comes with gasket for that area too. The bestie says we need check the intake manifold. (Kinda waiting to do that cuz it looks like it's going to be a bitch) car isnt over heating. Idling... kinda rough... the fiance and I knew the exhaust manifold was going to need to be replaced. But... really could it be the intake manifold?
What data do you have? You never gave any data.
This is why California needs to do away with emissions regulations. Codes like this will bankrupt people. We just need to get to live our lives... Car runs great why should it matter if there's a point .001% error in it's air fuel ratio. Come on California you are killing us!!
This is actually common on the 2v tritons. The superduties seem to be the most sensitive to it because of the nature they are used for. It can cause flooding out if the leaks are bad enough because the computer is constantly trying to richen the fuel up, my farm truck is throwing that code currently because of manifold leaks and a bad y pipe. The previous farm truck that was wore out I would occasionally have to shut it off for 4-5 minutes to dry the cylinders out otherwise it wouldn't have enough power to go past quarter throttle.
Mind you the flooding situation was only with a loaded trailer where there is a excessive load on the engine, just driving 15-20 miles was no problem but you could smell it was running extremely rich. Fuel pumps can cause a similar situation except for it won't run rich it just won't have enough fuel to do more than idle.
Thanks, in addition to that,i suggest if you try block or reduce the exosite at the end of the tail pipe, this could improve the system even at idle.
Ok, in case there is a language problem, please ignore that, since my native language is German. I might not be too exact as far as my grammar is concerned. (I will not spell vacuum, VACUME, ok)
I am writing this answer because:
1) as far as aerodynamics are concerned there is always a specific shape (airflow across a wing or through a venturi tube) involved that I could not find in any exhaust.
2) any pulsation would average out (just my opinion, no proof).
3) I am not trying to come up with new theories, so I did drill holes into the exhaust before writing (I do agree with You about testing first) and the holes in a Saab 900 exhaust blow air out anywhere I drilled (and it is hot :-).
I know there are airflow problems in intake systems (standing waves) and this may well be the same with exhaust pipes but I could not produce any vacuum anywhere and in Your video You had the same problem.
If You are able to show any vacuum in an exhaust system, I will gladly erase my comments.
Greatings,
Bernhard
Agreed- neither of us has proof, You are correct indeed that I also failed to demonstrate my theory as well.
I have long been waiting to revisit this video and do exactly that- will keep you posted.
I was just pulling your string on the grammar thing, no offense intended.
Matt, I guess that snuffs out my idea of a small exhaust leak on that 320 hp Beast of yours! I have to agree with you. After you had to unscrew the O2 sensor ( Wide Band ) all the way out to get any noticeable effect on the Trims, that a small leak is highly unlikely to cause a lean condition. That still doesn't mean I'm giving up on a bad O2! I went back and reviewed the Scan Data in the last vid ( Test Your Lean Condition P0171 / P0174 Diagnostic Skills! ) several times, to see if I could spot any abnormalities in the traces. I notice that in your garage, on frame 5220 on the LTFT, it was showing a lean condition and adding fuel.The STFT was taken fuel away, like it should, when you were opening the throttle plate. At the same time the Bank 1 O2 and Bank 2 O2 was oscillating from full lean .100 mv to full rich .900 mv, but the Bank 1 O2 seamed to be way more active and had tighter oscillations then the Bank 2 O2. Then at frames 5440 thru 5500 LTFT showed lean again and started adding fuel, but if you look carefully the Bank 2 O2 seems to again be more active then the Bank 1 O2. I could not make out what frames you were on when you were on the road, but if you look real carefully the same seams to occur, just not as severely. I still betting on a bad O2 on Bank 1. Also, when you first came off the throttle stop in your garage, I thought I heard the engine stumble, both times you did it. If that is so, that would definitely justify that injector balance test. Question for you. I don't own Autoenginuity, but Why don't the frames on all three graphs match? Are they set to different scales?
Billy R Billy first of all, 320HP? Really? What am I a riceboy? Jesus Billy. That car is 359rwhp and was Dyno tested to prove it at L.G. Motorsports in Plano, Texas a few years ago while I was on vacation.
Now that the important stuff is out of the way, I agree with you 100%. Initially, my first thought was an exhaust leak on Bank 1 on that car and my second thought was weak O2 sensor (for those of you wondering what we are talking about this is in the video "Test your lean condition diagnostic skills"). But given the data from this video, I have virtually eliminated exhaust leak now.
HOWEVER- look at JohnWrench's comment above which may change your mind back to exhaust leak.
Schrodingers Box First of all, let me apologize! 359 hp at rws, Wohhhhhhh, Don't punch me in the throat! I once owned a 1971 T-Bird with a 429cui V8 - 360 hp, came that way right off the showroom floor. Now them were cars!
I maybe going out on a bit of a stretch, but as I was watching this vid, (Diagnosing Lean Condition from Exhaust Leak with Scantool P0171 P0174) and you came to the conclusion that you could not get the O2 to react until it almost fell out of the exhaust. I tended to agree with you, but something in my head kept thinking about airplanes. ( I love anything that flies) On a wing when the air on the upper side, due to its curved shape, speeds up faster than the air on the underside. The air on the upper side than becomes way less dense than the air on the underside and generates an immense imbalance or pressure/force called lift. Could this same phenomena be happening on your car. When your at idle, the pressures inside the exhaust are greater than the outside atmospheric pressures. When you start to come under a load and the gases heat up,expand, and speed up, are we witnessing the same effects as a wing demonstrates. As the gas speed up inside the exhaust and become less denser and the atmospheric pressure outside the exhaust become greater it would force air inside causing your lean condition long enough until the trims overcome the air coming in through a small leak. Most of your viewers are probably going to think that I might need a vacation or something, but you being a scientist, I thought you might see where I am coming from. But hey that is what this channel is about, to get your viewers to think out of the box, right!
I know the most likely or conventional thought is a fuel delivery problem, but the way you romped on that bad ass 359 rwhp, it didn't sound like it was staving for gas to me! Now if you had oscilloscope, we could tell if that O2 was dropping out lean or not. Your scan tool is just not fast enough!
Oh, by the way I like gojududes suggestion, Mattometer is awesome, but I would add Mad-Mattometer!
Billy R Wow, I wish I read Johnwrench's post before I posted mine. That man is on the ball! I salute ya John! Matt, you should never say never. You just might have to check out his theory to get to the bottom of your mystery! Let's hope not!
Technicall Billy, it doesn't matter that you read John's post after yours- you made a completely logical conclusion that was based on the data available you had at the time. It is the thinking that is most important, and you were dead on. As new data comes available, good thinkers have to reevaluate how this would affect their original conclusions- and you did that too. Data may come and go and be found to be inaccurate at any time but good thinking is a constant. So either way, you "get it" and are not wrong regardless what the problem turns out to be.
Thanks, Base on the symptoms or should I say lack of symptoms (No dry misfires/hiccups), the response of your engine and the fact that it is only effecting Bank 1, the evidence most likely points to either excess air is entering down stream from all engine sensors and up stream from the O2 sensor. There has to be a factual and logical explanation of where these extra O2s are coming from. Or you have a faulty O2 sensor! If indeed, air is entering upstream of the O2 sensor, I think Johnwrench's theory is more plausible and logical over mine. But it wouldn't hurt to do a injector balance test to rule out a sluggish injector (low fuel delivery) since you have ease of access thru the Schrader valve.
one tip to remember, if you can't hear it really good (but still have an exhaust leak) it'll set a P0420/P0430. The broken bolt/cracked manifold is common and is a cause for the P0171/P0174, but if they are set with the 420/430, then the 420/430 set first, as the monitors won't run with the lean codes set. In my opinion, this is your best vid. BTW, you don't get it named the mattometer or anything like that lol
Thanks GoJo but i cannot see how an exhaust leak could possibly cause a P04x0 code because there is no way it would cause mirroring of the front sensor (unless the leak came and went in perfect synchronicity). If anything the leak would prevent getting the 04x0 code even on a bad cat because the fixed lean signal would throw an O2 low voltage code and you cannot get a catalytic activity code with the other code set.
I have also seen exhaust leak before downstream o2 cause p0420
Schrodingers Box HI, Matt. I am also a scientist by day and auto repairer by night/weekend. I tend to do more collision repair than engine diagnostics, although I am certified in both. I really enjoy the videos and your approach to diagnosing and not just guessing as most tend to do. I actually had a car come in recently with a P0420 or 430, can't remember. The vehicle had just had the engine replaced (Cats working fine prior to engine replacement), and the shop did not reattach the exhaust correctly. This leak was audible and was the cause of the P0420. Just enough air was being pulled into the exhaust system to cause this. I can't remember which joint it was as I did not do the repair, but it was near the front of the vehicle. The shop was on the hook to redo it and the MIL has stayed off since.
Sam Graham Being that you are a scientist, did you validate that the rear trace was not congruent with the front O2 trace after the repair to confirm that indeed there wasn't ALSO a weak cat along with the leak?
I wish i had been able to, but i did not get the vehicle back after the repair. I see this customer weekly, and he has not gotten a MIL since. Not the most conclusive evidence, I know, but it made sense since there are pressure pulses in the exhaust that create vacuum as they flow through the system and the condition did not exist prior to the engine swap. Just wanted to mention this to you as a possibility in future repairs. Keep up the good work.
I like the idea of bringing diagnostic skills from another profession to auto repair. I've had the same kind of thoughts about new diagnostics for engine cooling systems, too. Problem is, some of the tools I would like to use (like doppler ultrasound to measure flow) would be a hard sell in a competitive market that can get by without expensive tools. To market a new diagnostic tool you need to show that it saves time or money.
Agreed- bringing diagnostics from other professions and integrating the tools of the trade is always interesting. I often wonder how a Gynocologist would approach some of these situations.
Schrodingers Box Getting at the engine via the tail pipe wouldn't be easy.
I should have watched this video earlier! This was exactly my problem on a 2004 Jaguar S-type 4.2 with 100k mi. Everyone kept saying I had a vacuum leak, because I had high fuel trims at idle which disappeared at load/speed . . . but just on bank 1. I'm a little deaf so didn't hear a slight "puff" exhaust leak at flange on Bank 1 . . . right before . . . cat . . . and wide band 02 sensor . . . One day my partner was riding in passenger seat and said "what's that noise?" It was so obvious once I figured it out . . . but only after doing every possible vacuum leak trouble shooting: blowing smoke in, replacing O ring on dip stick, propane around lines and into air intake to test O2 sensor watching for neg STFT, misting water, BK44, Scotty Kilmer's "plugs and wires" (I did plugs since I was at 100k anyway) . . and some stuff I forgot!. But deep down, it never made sense to me that a vacuum leak on the top of the engine would show up ONLY on Bank 1 elevated fuel trims at idle. I used a little Kroil and a breaker bar to free down pipe flange bolts and re-tighten . . . by hand . . . carefully . . .Hopefully I can be as logical in the future and avoid a bunch of unnecessary trouble shooting . . . and parts buying. But it was a great learning experience and I really enjoyed . . . thinking! I now know the mechanic I consulted at first (before watching your videos). . who pulled out the MAF sensor, cleaned it, and cleared codes. . . was an . . "idiot" . .. I believe is the proper techincal term. Now I just have an intermittent P0105 MAP code to deal with. Hence my question to Bernhard. Thanks Shrodinger!!!! I could never afford to own this jag if I had to pay for everything to be done to it! I am glad I didn't change the O2 sensor. But I am SO afraid to replace the O2 sensors . . .and get called an idiot . . .that I probably won't even when it ends up being the problem!
Please write to me:
bernhardlist@hotmail.com
And I will help!
Greetings
Dear Matt
I really like Your approach to troubleshooting, so keep that up.
Yours is the only channel I have subscribed too and I don't want to depend on Eric the Car Guy. I will be the first to watch Your video on exhaust leaks and I thank You in advance for finding the truth to improve problem solving, that is all that counts.
With Lufthansa have been trained to troubleshoot a problem and not the captain alone decides on how we die :-))))))
Greetings
Bernhard
PS: Sorry we at Cargo don't have Denver in our schedule, else I would love to meet.
Many Thanks Bernhard. Yeah with your engineering background, ETCG is not going to be of much use for you. He provides great value, but generally for people who are beginners or need their hand held through a procedure (which is fine, most people by far are novices). But for people who know how to turn a wrench and what they need is advanced theory and background on automotive systems to be able to do advanced diagnosis and troubleshooting, this is the purpose of my channel. I believe any DIY that invests time to study can do advanced diagnosis as good as a professional. It's all a matter of spending time to understand some fundamentals and of course developing the scientific thought process. Good for you bro!
Schrodingers Box 2002 hyundai santafe 2.7 trouble code p1167 , b2s1 and maf were replaced but fault code still found. o2b2s1 is stuck rich even in closed loop the same time stft runing lean around 24 , it is strange lean stft and rich o2 sensor signal. any comment?
abdullbasit osman It isn't the O2 sensor or MAF obviously.
What data do you have to help with a diagnosis?
i mean oxygen sensor b2s1 show rich all the time (stuck rich at 0.7 or 0.8 mv ) but stft shows lean stuck on 24 why it is not -24 ?
because the fuel trim is maxed out and still not meeting demand.
My truck is doing this. Bank 1 HEGO reads lean at idle (sticks around 0.30V), and being a V8, I can compare bank 1 to bank 2. Bank 2 switches at idle, rich/lean. If it were a vacuum leak, both banks would read lean. Under heavy load, both sensors read ~0.90V. Interestingly, my scanner said "closed loop, operating on one oxygen sensor due to system fault). Awfully intelligent PCM for a 96' (first year of EEC-V & OBD-II). This is with long tube headers. They didn't fit well, and I had to modify a primary tube to clear the starter. Well, my welding wasn't too great, so a leak is probable...first time using flux core stainless wire did not go well.
Yes the phenomenon you see is a "OL3" where it is a special open loop that disregards an O2 sensor that is not giving proper function.
a misfirer will also cause an OL3 condition.
I would transpose O2 sensors on B1 and B2 and if the lean condition moves, your diagnosis would be 100% - O2 sensor bad.
I was thinking that the main difference between vacuum/exhaust leaks would be whether the fuel trims make the situation better or worse. Could you reset the trims to zero, and then start the car cold in open loop?
I would imagine that if your car starts out rough with 0% fuel trim, and smooths out as the trims start to increase in closed loop, you're probably looking at a vacuum leak. If your car starts smoothly with 0% trim, and only has a rough idle in closed loop, you're probably looking at an exhaust issue.
Sorry, kind of new to all of this, and I know it's an old video.
I have P0174 code now and I suspect that it is due to an exhaust leak. This is clearly not a problem of the mass air flow sensor, not a leak in the intake manifold hoses because they would also cause P0171 at the same time. I have been driving fast in bad gravel roads for two weeks and heard occasionally loud noise of rocks hitting the underneath of the car. Also, as you have said, I can clearly hear abnormal exhaust pipe noise.
Pretty simple. just curve the fuel trim against load to confirm. If t correlates your suspicion is wrong. Easy as that.
@@SchrodingersBox I don't even need that. I already found the leak. I can hear and feel the hot air coming out of the leaky pipe section before the converter on bank 2.
Then that cannot be the cause of the lean code. It is after location of B2S1
@@SchrodingersBox Just to let you know. I'm new in this, 1st time using an obd tool and trying to solve a problem. I appreciate your prompt response and comments. I respect a lot your opinion s. I replaced that section of the exhaust that contains the flex pipe and erased the p0174 code. So far, I have not got a chance to drive the car a lot. 2 sensors EVAP and O2S22 remain not ready. But the fuel trims are now around -15% which seems to have resolved the lean problem. This is a 2002 Toyota highlander.
For wideband O2 sensor the reading is made in the current flow, not voltage. I think I am not wrong, but I learned this on the internet so we never know.
Hahaha you are no wrong at all. it is absolutely read off current flow. the voltage strictly for reference only. it isn’t actually real voltage. I have a video on this in fact.
Wouldn’t the exhaust gas push out the leak and not let air in and the sensor reads the same because the mixture is the same there is just less exhaust as a whole. It would just think it’s a smaller motor by barely?
Great video 👍🏽🔥
Okay so what you are saying is that if you have a large enough exhaust leak, it can act like a Vacuum leak, and there is no way to differentiate between the two other than you would hear smell and definitely be able to tell there is an exhaust leak before the O2 Sensor. I have done a smoke test, I have done carb cleaner test, I have done a water test, and I have tried pulling off vacuum lines to try to find the problem and putting them back on to check for engine changes in Fuel trims and RPM, Sound etc. I pulled everything off of my manifold and plugged all of the vacuum lines completely and it still is idling rough, but once I throttle it up it runs perfectly. I am experiencing symptoms of a vacuum leak. However the other day I did notice that on the passenger side I am smelling exhaust when I rev on the engine. Your videos are helping. I am going to check the bolts on the export manifold on the passenger side and see if maybe they may have come loose. My codes are also Po172 and PO174 System too lean Bank 1 Bank 2, LTFT are both at 25% STFT fluctuate, but on Freeze frame I see 3% STFT Bank 1, 5%STFT Bank 2, Code was thrown at 880RPM 20%TP, MAF 0.03, B1S1 .323, B2S1 .788 B1S2 Steady after cat doesn't matter because it has no fuel trim. I am seeing the voltage on the side I suspect the leak is on is lower by quite a bit. that would be Bank 1 Sensor 1, I suspect a rather large Exhaust leak on the side with Cylinder 1, since it is a Ford 460 7.5 Liter V8 That would be the passenger side. That is where I smelled Exhaust wafting up when I coddled the Throttle the other day. Thank you for providing a few Ideas for me here. And the learning experience. More of a Reconfirmation for me.
(Note my Freeze Frame Data is going from non specific Memory on the Short term Fuel Trims and the O2 Sensor Voltages, so it may not be accurate: Most likely not!!)
You don't have thje relevant data to make a diagnosis. All that and I still don't see FT curved against load??
Awesome video Matt. Old one!
1) is your LTFT also maxed out?
2) how does Bank 1 compare?
3) do you smell unburned fuel at the tailpipe? (watch out for your CAT!
4) is this the new O2 sensor that shows rich?
Woah - you dared to dis Scotty!? LOL. Enjoyed the video - useful.
I have an in-line 4 that falls on its face at about 3000 rpm and even back fires. idles OK. after a few seconds in this condition back to idle at 1700 rpm the STFT goes -17 to -25 . The LTFT never changes at .8. I am lost at this point. help!
I'm guessing valves?
@@charlesgould8436 I'd be much more suspicious of a blocked exhaust - I've seen it with plugged cats, and bent tail-pipes. In the winter I'ved seen it with condensation frozen in low portion of exhaust.
Just had the 0174 code from a manifold to pipe leak
Reconnected it and code is gone
Should’ve made it leak from the manifold flange I think I’m dealing with this rn on my 06 mustang gt I straight piped it the manifold studs broke I did not drill them out completely center and didn’t have a Dremel with carbide bits to get the remainder of the bolt out to make it fit as it should and it didn’t completely seat and with my car supposed to be loud going at it by listening to it is gonna do nothing my car is also cammed and I think with it chopping at idle it’s helping air get into the exhaust bc it’s not a steady stream of exhaust and there is definitely a big manifold leak bc I can smell exhaust gasses through my heat at idle when I’m stopped so maybe you can do it again this way?
Maybe, just maybe the difference between a vacuum leak and a exhaust leak would be that long term fuel trim. Maybe try a vacuum leak and see if that LTFT goes up and doesn't with a exhaust leak? I kind of went over it in my head and I don't know if you tried that or not but I wanted to through in my input just in case. It's always great to here other people's input.... sometimes.. haha!
Vacuum leak diagnostics IS our established baseline, rememeber.
We are using the established diagnostic for vacuum leak as our control. This would be high FT at idle that correct under load.
Schrodingers Box Oh yes, that's right!
Schrodingers Box Here is one for you, a 2010 Kia with no MAF and no EGR Valve. I haven't found out why or any research about it, but I was wondering if you knew anything about it?
No MAF is very common. The engine design is known as "speed density". It uses MAP only, no MAF.
Also many cars do not use EGR. I don't know the specifics exactly on how they "get away" with that though- maybe some modification to the catalyst system?
Schrodingers Box I have seen some Civic with no MAF and no intake snorkel lol but never no EGR, it surprised me when I hooked up my Bluetooth scanner and saw no supported PID for MAF and EGR. I'll definitely have to do some more research on that. But you have inspired me to do "charitable mechanic work" for people with low income or people in need. So I do have to say thank you for that!
I would think with an exhaust leak that the short term fuel trim would gradually go positive until a CEL was lit if the car was left at idle for a long period?
My thinking is that since the computer cannot make any adjustments to change the fact that the O2 sensor is picking up additional air, it would continue slowly increasing the fuel trims until it maxed out assuming the fuel doesn't foul up the sensor or snuff out the oxygen. Once again at idle with no load.
My honda right now i am pretty sure has an exhaust manifold leak. WOT and the fuel trims are perfect zero and driving down the road the car is fine... But as soon as you idle it it will slowly over the course of maybe 10 minutes hit +10% STFT. With the backpressure if i get it negative it smooths out its idle.
I wonder if creating the exhaust leak further upstream of the O2 sensor (for example, perhaps at the exhaust manifold/engine interface), would allow for more time for the air to mix before it reaches the O2 sensor and then cause a "clearer" lean condition in the data streams.
yeah there is also a possibility that a leak at the manifold could increase “scavenging” effect and draw more O2 in than it would further downstream. I have been meaning to test that.
this equated to "Vacuum leak" symptom it was just unmetered
So would that mean a "vacuum leak" could just be the from an exhaust leak ? I did a smoke test from the engine bay with no smoke.
You can try doing smoke test at exhaust pipe and checking for leaks.
Thank you chief
Do you think that the sensor you loosened might not have captured enough oxygen that you could have seen it on the scanner, due to the length of the sensor and the exhaust moving the oxygen past the sensor and missing the sensor area of detection. if this makes any sense. I think, not know, if you had a leak further upstream the sensor detection area might have picked up a little better, the amount of oxygen caused by the leak. Your vedios are the best, and I watch then over and over again and thanks to you, I am? learning. thank you.
Yes it makes sense and I agree with you. If I get a chance I will repeat this with a better exhaust leak model.
The exhaust leak does not HAVE to be upstream of the sensor to effect the fuel trims - depending on the exhaust design reversion can cause the sensor to read lean 8 or 10 inches upstream from the leak - - - particularly at low engine speeds with relaively high overlap.
Restricting the exhaust at idle to cancel out the reversion effects (negative pulse) should force the STFT down at idle if the lean code is caused by exhaust leak. (shove a potato up the exhaust with a 1/2" hole in it with the engine idling)
Yea, I was wondering what Matt was trying to do here as well. Unless you're expecting some sort of venturi effect creating a vacuum to be in place why would gas coming out under pressure cause oxygen to get into the system. Completely different deal than a vacuum leak. As an electronics engineer I put everything into electrical terms in my head. With a vacuum leak you have electro-motive force in the direction of oxygen getting into the manifold, here the EMF as it were, is pushing the gas out. With the gas coming out how does the oxygen get in?
I know of several cars that have diverter valves in their exhaust systems that switch from wide open headers. (race trim as it's called) to cat systems and mufflers (to satisfy "The Man"). When they hit the switch I don't think their check engine lights come on. They do get louder and have more power with the valve open (or so I've been told since I, as a law abiding citizen, would never do such a thing). The fluid dynamics just seem wrong to me for exhaust leaks to affect fuel trims.
Precisely SATAMAN. The experiment was designed to allow for the possibility of Venturi effect, and I show it does not exist in an exhaust leak.
Now, that said- what I showed is it does not exist AT THAT LOCATION, and that is correct. I did not think the location mattered. What some people are saying now is there is a dramatic difference if the exhaust leak is between the exhaust manifold and the head. In that event, supposedly, "scavenging" of the exhaust will suck in outside air similar to a vacuum leak. I will need to repeat this test with an exhaust manifold leak to see if their theory is correct and increasing RPM would actually cause more of a lean condition instead of improving it.
Pre-cat I've seen an exhaust leak pull air into the system as well. Both of you, well said.
DE Nichols No sir, you did not, when the rear O2 wetn more positive, like this Air Fuel ratio going more negative since it's opposite, I was having no venturi effect. I have now unwritten invalid memory in my head.
DE Nichols Argh, I think I have to rethink this and watch the video again. I may still have it wrong from the effect on the video versus under my car.
DE Nichols
I think this is final data, and I may need help understanding it. When I had almost sealed the pre-catalytic converter leak, post bank 1 sensor 1 O2 sensor, the downriver O2 sensor no longer reported rich unless there was a lot of rich driving. When there was a leak it'd go rich regularly.
I believe the exhaust was only escaping. When it would escape worse the downriver O2 read more rich...that makes more sense to me if it's pulling air in, so I'm officially lost as to why that O2 sensor read more rich.
In the unlikely event that there are 0 codes but your fuel trims are shooting from anywhere from -7.8 to positive 28 with low voltage to the post cat sensors what would that be exactly?
Sounds like a lean condition
I'm curious to see what would happen adding a little bit of propane to brake booster and see how that changes things. I would bet an air leak cause by exhaust leak would be more visible because it's closer to o2
Just a thought
Agreed- I want to do O2 sensor response tests and see if they are equal on the banks or if Bank shows less response.
Matt, whay scan tool are you using? If it is affordable I might buy one. Thank you.
in this video it is AutoEnginuity.
Hello too the channel I was looking at all the videos and the one ting that I was told if your going too use a aftermarket or reman maf it could make your life go crazy. Plz use oem maf from the dealer 😔😔😔 I hope you look at the Maf again because it the hold all the spac
I came in just hoping you could differentiate an exhaust leak vs vacuum leak just with the scantool, have you since found a way yet? I'm tracing a slight lean condition, and the signs are pointing to one of these. Does a vacuum leak always result in a higher rpm at idle? Wouldn't the ECU compensate, and keep the idle speed normal?
The IAC will reduce idle speed on a high idle from a vacuum leak.
had lots of fun...
the pressure inside exhaust pipe is much more the outside air pressure,so how outside air can get into exhaust pipe?
Because of Bernouli Principle.
thank you very much
Interesting, but I think we need a lesson on venturi effects.
That blue BMW R100Rs motorcycle (pictured) has venturi air injection to burn off hydrocarbons in the exhaust system. It is an intentional air leak into the header pipes, and the air is drawn in by a purposely engineered venturi just downstrean of the exhaust valve.
Exhaust system pressure has to be greater than atmospheric pressure for exhaust gas flow out of the engine. So the question is...... is the average exhaust leak going to act as a venturi and suck in air, or act just like a leak and let out only exhaust?
If the leak is acting like a venturi, then leanness might be detected. If the leak is just a leak, then the sensors won't detect any change.
Check out the thread started by SATAMAN it seems that depending on where the leak is, it can have a venturi effect, or just be a leak.
DE Nichols
Thanks DE N.
Have you thought about making dvds?
Do You smell unburned fuel at the tailpipe?
Red for sensor black for trim
You must be testing us to see if we are paying attention.
At about the 8:44 minute mark the color codes are right but the labeling of the lines is reversed.
Ah yes, I only pay attention to the color coding so I didn't really notice the locations where I put the labels. The location of the labels in the legend is not meant to be significant, only the color is, but I can see now how that might be confusing. I will consider that next time.
The issue I have with this reasoning is that is there a positive pressure or negative pressure where the exhaust is assumed to have the leak? O2 entering would be possible if the pressure there is less than the outside pressure. I am guessing that is NOT the case. So please *now* explain how you are getting extra O2 to be read by the A/F sensor under the condition.
Did I miss the baseline readings where you looked at the waveform with NO LEAK? Do you not see pretty similar AFR vs RPM graph with OR without the exhaust leak? My apologies if you showed that experiment and if indeed the graphs were drastically different.
12vgs8606 Yes I see your points and I can address them
First off and most important, you did miss where I did the control validating the waveforms with no leak- it is the single most important baseline to do and had I not done that, I should quit doing videos! You may have missed in my explanation of the A/F and equivalence ratio data outputs. And of course, the non-leak control showed normal response.
For the positive pressure- there is absolutely positive pressure in an exhaust- evidenced by the facts that you "feel" an exhaust leak with the puffs through the leak as opposed to a vacuum and also by the fact that I was unable to do any WOT testing because the loose O2 sensor kept blowing out of the hole.
This is why I had to generate such a surpringly large leak to get O2 in the system. By just having the sensor threaded very loose, no leak was detectable.
Presumably, air might also be forced into the exhaust leak when the car is moving I suppose.
I am still missing your baseline test where you increased the rpm and watch AFR. You did the snap throttle test but did not do the steady increased rpm test. Come to think of it, you did not have RPM as one of the parameter being monitored on the scanner but it was on your whiteboard!
If there is positive pressure, why are you then showing air entering (aka extra O2) through the hole?
Bottomline:- we both agree that undetected i.e. minor leaks in the exhaust does not seem to have much effect on drive-ability or the fuel trims.
12vgs8606 Wow you know what... in editing I clearly must have accidentally eliminated the reving baselines that I did. Shoooooot. My bad! But I did do them and they were fine. Fantastic catch. Damn now I got to pay more attention while editing as I do filming and fixing!
At least I was not going crazy! So, without the leak, O2 and FT remained flat plotted against RPM? That alone would be a good diagnostic tool! For some reason, I was under impression that there is no such thing as "the" fuel trim but rather a multi-dimenional array of fuel trims or "cells" of fuel trim data based upon key engine parameters such as RPM and/or load. If that is the case, chances are fuel trim may not be constant against the RPM even in ideal cases where there is no leak.
12vgs8606 You are correct- fuel trim is done in "blocks" but since I did reset the fuel learn or disconnect battery or anything, the test I did is valid both for control and variable.
Is there any way an exhaust leak would only affect bank 1? My LTFT and STFT is at 25% at idle, but when RPM increases the STFT rapidly decrease eventually (actually pretty quick) reaching -15%. LTFT will slowly drop usually to 12%. My truck will start running better and stop misfiring at these fuel trims. The check engine light use to blink for cylinder 2 misfire but now I get no code, although, I feel the misfire at idle. A vacuum leak or intake manifold leak is the only issue that makes sense to me so far. Can it be anything else?
can’t really tell with that data but yes it is possible for an exhaust leak to affect just one bank.
@5:27
"...but don't worry, I'll explain whether the procedure worked or not - if you're too lazy to go look at that..."
LMAO You have such faith in your viewership. lol
i have a lean condition only at idle,i have a wideband o2 and guage that exposed the lean condition,further investigation i found major leak between turbo and manifold right before the factory o2 sensor.i can feel the exhaust leak with my hand,my question is how does the leak suck in air to cause the lean mix is it valve position or overlap or venturi effect? im trying to understand why ths happens,thanks.
Venturi effect. Most people think that there is a constant “outward” pressure from exhaust but remember it happens in “pulses” and even then it is a really low pressure - far, far under a PSI. The oxygen can be drawn in and in fact I have a video somewhere proving as much.
@@SchrodingersBox thank you for your response one more question for you,on a turbocharged motor can exhaust leak cause rich at wot in full boost? i had to order new exahust manifold gasket for my lean idle but all a sudden im having a rich condition under full boost with the lean idle,with the exhaust manifold pressurised is this pressure leak in exhaust causing the new rich condition at full boost? whats your thoughts?
ps my afr at full boost days ago was around 11:2.1 ,now its 10.0. so not sure if the o2 could even add this much fuel?
update: checked codes and found knock sensor code.i beleive the lean idle caused some idle knock which threw this code,im thinking this code may be pulling timing and adding fuel under boost as protection does this sound like the correct theory?
It sounds like “a” correct theory but not “the” correct theory. It would be “the” correct theory of you could see ignition timing correction from the knock sensor.
Man I wish you were located in Chicago.
I have taken my car to about 4 shops and no one can figure out my p0171 code. I have a 2005 Honda S2000. It has rough/stumbling engine at idle. I’ve done the following - fuel pump, injectors, fpr, pcv, iat, map, valve adjustment, o2 sensor, checked for vacuum leaks, brake booster, iacv, replaces intake manifold gasket, checked for exhaust leaks, and tried a different ecu. Compression is all within 215-230 what else can I try? Can it be a burnt valve or slightly bent valve? My car drives fine but my fuel trims stay really lean 15%- 30% thank you and I hope to hear back!
What data do you have? You say the MAP was changed- what was the MAP data that indicates it was faulty? Intake gasket was replaced- what was the fuel trim data indicating it was faulty? Fuel pump was replaced- what was the amperage under load that indicated it was faulty? You have to give the data you are using for all this.
Schrodingers Box hey thank you for replying! Unfortunately I didn’t come across your great videos until recently. The parts mentioned were replaced without actually gathering data like I should have. I’ve been watching a ton of your videos. I’m still learning a lot. I just made a video and posted it on here so that maybe you can see what I’m looking at easier. It really hard to explain it all and I know it’s hard for u to tell me without actually having the vehicle. Let me know what I can record to maybe have you better help or give me advice on. Here’s the link to the video I made. Sorry I’ll try and get an actual video of the data from driving around.
czcams.com/video/nuEBYdy1gyk/video.html
Yeah sorry but I would need relevant data in order to get a direction otherwise I’d be throwing parts at it too.
The FIRST thing you need to do is a cyl leakage test. This will detect ANY valve issues. Next is a "dynamic compression test" or "power balance test" - basically dissable one injector at a time and compare the rpm drop with a sensitive tachometer. This will point to which cyl has an issue (valod even without leakage test - but will not pinpoint the CAUSE of the inbalance - which the leakage test WILL if it is "mechanical". (In the old days you did this by shorting the plugs one at a time - but that can harm catylitic converters)
They also checked for leaks and found none.do you think it could be the map sensore.
Absolutely it could. Right now we can rule it down to anything which determines idle control, fuel ratio normalization, load detection and response, or even mechanical.
Which means everything.
See my response below.
If i have only one cylinder on single bank exhaust leak, will it effect both banks ?
No. it will affect the bank it is on.
@@SchrodingersBox i can hear ticking noise from passanger side head and unburned fuel on exhaust manifold or inside ex manifold. U can check my channel last vid
sounds like an exhaust leak to me!
On my 4.3 vortec engine (at idle & in closed loop) I have LTFT readings of about 12.4 (both banks) & a post cat O2 reading of 0.08. The LTFT goes down and the O2 readings go up (but not by alot). I going to pull the O2 sensor and test it but if this is an exhaust manifold leak would introducing propane to the exhaust manifold bring up my O2 reading and improve fuel trim, or is there anything else I can try short of pulling off the manifolds to inspect the gaskets?
Any suggestions would be appreciated.
See my video "secret of engine problem diagnosis:fuel trims" which details how to do the exact diagnosis you are attempting.
lean condition. exhaust leak or intake leak(or filter mounted directly on a maf sensor! . definitely causes your car to compensate. (test it you Wil see.
i’m having a p0171 system lean bank 1. i do have a pretty substantial manifold leak and a exhaust flange leak ( can hear it very clearly) my fuel trims at idle are 25%. obv the leak is before the upstream 02, could this cause my “lean” condition? chevy 6.0 vortec
It definitely could. Curve the fuel trim against load to be 100% certain.
so under load it’s dropping down to a 11-18% would that be a fuel pump issue then? or clogged injectors? i just ran some sea foam through it and that seemed to make it even worse than it was before
Looks like a leak to me. You have to fix all exhaust and intake leaks before a fuel trim analysis can be conclusive.
What was the seafoam supposed to do? I don’t see how that is going to correct a fuel trim anomaly under load.
originally this all started bc i was noticing my fuel consumption was abnormal. yes ik a 6.0 is a gas hog but im talking maybe 8-9mpg highway and down to 5mpg climbing hills. i thought the injectors were out of whack so thats why i bought the sea foam to try and clear them out.
someone had also cut the bank 1 sensor 2 02 sensor and i hard wired it back in and then it started giving me a p0171 code
If your sensor is cross threaded like mine was it will leak alot and throw codes. Mi e threw po420. I couldn't hear it untill I crawled under the car and had someone rev it!
Not possible. How did it cause superimposition of the signal from just a leak? Impossible. Did you also verify AFTER that the leak didn't damage the cat and cause loss of activity? Did you validate actual catalyst activity?
I have yet to ever someone who has.
@@SchrodingersBox you were right. Light came back on. Cat was broken up inside. I gutted it yesterday and now I'm getting a po171 lean code lol
Any chance of an exhaust leak AFTER the front AF sensor causing a lean mix or throwing an AF sensor code?
How would that happen? Are you inferring significant fuel trim adjustment occuring from the S2??
Schrodingers Box Mechanic said that if the leak is near the sensor, O2 could be introduced into the stream, or exhaust gas could rise into the engine compartment altering the reference air.
@@alalan3735 it has to be upstream of the sensor in order for the sensor to read it. If the oxygen is introduced into the exhaust system downstream of the sensor, it will never cross over the sensor, so the sensor will not be able to read it.
My Drivers Side Exhaust Manifold Ticks On My 2006 F-150 Which Gives Me a P0174 code on Bank 2 Drivers Side.
As would be expected. The oxygen from the leak contaminates the exhaust causing a false lean.
I'm thinking about switching to headers instead of Manifolds....Wonder if this would make a Difference?
Well it will fix the P0174 if it fixes the leak.
Or just replace the gasket if that’s all it is. Last ford truck I worked on with an exhaust tick, it had a broken manifold bolt nearest the firewall.
Hello,
Do you think an open exhaust valve would cause the same pattern? I'm curious because my car has a high LTFT that is not from the vacuum leaks or an exhaust leaks.
OlamDao What is your compression test result?
+Schrodingers Box good suggestion
+Schrodingers Box Sorry for late response. Somehow youtube messages show up in my email box late.
Of course, compression test how did I miss that. Thank you for the reminder. And nope the exhaust valves are not the problem, compression are within spec. all six are around 190 psi +/- 5. So I guess back to more diagnostic.
removed battery to be able to have more room rereplace a headlamp, then engine light came On, had it checked then this is the code (0P106),Replaced it!!, then it worked for 3 days.(engine light still on) returned part thinking it's bad, put the original part back on ,(engine light still on) finally took it in to a dearlership service dept. they tell me I need to replace the ECU/ENGINE COMPUTER! but before that I had a personal mechanic look at it and he said there is a engine leak! This Corporation just "put out" a 2nd revise RECALL on Engine replacement BECAUSE of a Engine block issue I am a Woman, and that may mean to some; tell me anything! But I don't like dishonesty it can be dangerous and most certainly wasteful TIME /MONEY!...YOUR VIDEOS WERE VERY HELPFUL UNDERSTANDING (wish I could take YOU with me to that service dept! ) I have no desire to spend $1200!!!! when It seems like the computer is working enough to give off code P0106!!!!! Any Positive suggestions are Welcomed not sure what to do next after I go pick it up!
I have engine 2tr no dtc with lean conditon with 88⁰c temp heating engine a while b1s1 at 14-23% and b2s2 at 0% at idle and i notice that the s2 doesn't folow to +.. put some rpm at 2500 it still the same trim no change at all. What could be the cause thanku
you are saying S2 doesn’t react? that’s correct. the catalytic converter is working then. S2 will stay at .8V if the cat is working.
@@SchrodingersBox yes b1s2 doesnt react on 700rpm and 2500rpm
At idle
Stft 20% flactuatng 14%
Ltft 0%
Rpm. 800
Temp 88⁰c
Pedal is on hold
Stft. 20%. Also flactuatng 14
Ltft. O%
Rpm. 2500
Temp 88⁰c
There is high fuel consumption
And trying to a fix .
black smoke comming out the pipe is present at sudden acceleration
@@SchrodingersBox is it a bad 02s2?
No- the O2 is reporting the issue, not causing it. You don’t have enough data to identify a cause. You need to show an actual load curve of LTFT and STFT against RPM.
@@SchrodingersBox I cannot figure out what is going on when I remove the af1 the result was nearly better.. I have reading at b1s2 at 9% and b1s1 at 0% and check engine light was there. No vaccum leaks change plugs IGN coils injectors cat coolant temp sensor MAF need further diagnosis of which I don't have. It's maybe a bad ecm Ive done it all changing outputs and inputs but still no changes.
Shots fired.
I ate a stick of butter with a fork today.
Hopefully the fork doesn't get lodged in your gut!
Hopefully it will so I don't have to live through a Hillary presidency.
Thank God we dodged that bullet
go iron shopping at walmart. Its more exciting.
RIP
interesting never think of this cause.
Well, just to be different, I'm going to address other areas that could introduce vacuum leaks with positive intake vacuum.
I really haven't a chance to study up on the LS1 configuration.
But, I'm brainstorming things that come 'on' during positive pressure... I know of purge valves and EGR valves opening during positive manifold vacuum.
So, I would completely replace the EGR system and purge system and perform tests again. Just kidding. Thought you'd get a kick out of that one.
I suggest using a hand pressure pump to test these solenoids, bi-directional communication, and/or smoke to test the valves. In addition, I would also display the appropriate PIDs, e.g. MAP, purge solenoid status, and other emission related devices, and snap the throttle to see if I noticed any correlations.
Just for kicks, I would hook up a vacuum gauge and ensure the needle is solid at all RPMs and at the appropriate values.
Now, I'm sure your response will be that these systems would affect the manifold completely. I agree with that, but I don't know the LS1 configuration, meaning perhaps these systems are hooked up to one side.
I tried to listen during the video and didn't hear any hissing. I thought I heard a little off throttle hesitation.
I'm sure I'm going to be totally wrong, but I would think an exhaust leak would affect the FT values at all RPM ranges. I would think we would hear the leak at any RPM, some more than others, on such a big displacement motor.
Lastly, thanks for sharing this experience with all of us. This way we all learn.
***** Man I will admit, you totally got me on the "replace the whole EGR system" lol- I almost threw up- really.
I need to revisit this video anyway since new evidence suggests the location of the leak may be a variable- a leak at the exhaust manifold itself would supposedly result in "scavenging" the outside air and creating more of a lean fuel trim effect. But whatever the case is- even if that's true- ultimately what I need is a way to differentiate the evidence of an exhaust leak from a vacuum leak using scantool data. I am not opposed to vacuum gauges, etc but I am looking for a scantool methodology specifically. Any ideas on that front?
Schrodingers Box
Sorry about you tasting vomit. LOL I didn't intend to take you that far. Just wanted you to laugh. I was going to pretend I put your issue on a forum and indicate they suggested it. But, I knew that might prevent you from reading further in my comment and miss my joke.
Well, I have used the MAP PID in graph mode to check out vacuum leaks, but to be honest, I've had better luck with the old school analog vacuum gauge since I wanted to see bounces, inHG, or slow response. Since the ECU, PCM is taking periodical digital samples from the sensor, I feel it just isn't the same. For example, a leaky valve might not be noticeable from a MAP PID but a gauge would show it straight up.
Shooting from the hip, I would run the car and use a water bottle and spray around intake and headers to see if I could hear the leak, which is going to be challenging due to your healthy exhaust system. I believe the intake would make a sucking sound, and the exhaust would sound bubble-like.
I understand you want to do it via a scantool, but it isn't bad to perform physical tests when the issue could be physical. Right?
I can't wait for your next video and what the real issue is.
I plan on using propane and a smoke machine to check for exhaust leaks. No need to check for an intake leak, as that is ruled out by the fuel trim at idle.
***** At about Matt's vomit moment, I was like, okay, please don't let this be real and, with my reaction less severe, I did have a pretty good laugh thank you.
...So, Matt, if my exhaust is leaking, it'd be best if I just replace all of it, right? ;)
How do i get in contact with this guy?
You just did
Pinhole on a cast manifold will cause a lean code. Don't forget to smoke test the exhaust as well as the intake when trying to diagnose lean codes.
With an exhaust leak you can have back pressure from the exhaust valve closing...thus the down stream can show more oxigen, a lean condition...duh
ummmm that makes absolutely no sense. how do you get backpressure from an exhaust valve closing
Doesnt make any sense
exactly Dad Dad. . if anything an exhaust leak would reduce backpressure. no idea what this guy is saying.
Informative video but why ya gotta diss Scotty?
because he is the index case for incompetence when it comes to car repair.