Low fuel pressure causing a P0171 and P0174 trouble code
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- čas přidán 2. 02. 2012
- 1999 Mercury Mountaineer 5.0 with a P0171 and P0174 DTC in memory. This is a great video on using fuel trim and freeze frame data to determine the cause of the lean condition.
Engine Performance Diagnostics chapter 4 pages 12-19
Symptoms
- low power
- lean exhaust trouble codes P0171 and P0174
- pinging
- hesitation
- surging
Fix
- replace fuel pump and fuel filter
Tests shown
- how to determine MAF sensor condition using BARO HZ data
- how to use freeze frame data to determine type of lean condition
- how to use STFT and LTFT at different loads to determine type of lean condition
- how to test fuel pressure with a gauge
- how to determine fuel delivery design
- how to measure fuel pump current with a scope
- how to locate the fuel pump inertia switch
- how to calculate fuel pump RPM
Tools used
- scan tool
- fuel pressure gauge
- Picoscope
- inductive low amp probe
Playlist
- (Chapters 14, 15,16) Fuel Delivery and Fuel Pressure Testing
• (Chapters 14, 15,16) F...
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Disclaimer:
Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of ScannerDanner LLC, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not ScannerDanner LLC. - Auta a dopravní prostředky
I CAN WATCH THIS VIDEO 1000 TIMES, AND NEVER GET TIRE OF IT, GREAT VIDEO LIKE ALWAYS PAUL!!!!!!!!! THANK YOU SO MUCH ,,,,,
You & Eric are awesome representatives for Rosedale. Wish I could afford to go there. The integrity that you guys give the automotive industry is invaluable. Hope you guys get some kind of sponorships someday like from an oil or parts company. Greatest respect for you two.
Idle lean and lean under load, I learned something new today, thanks Paul.....
Wish I could go to your classes!!! You are such a good teacher!
thanks for all you do brother watching your vedios is inspiring
60psi is definitely the right PSI for that engine. Was working on a Explorer that would crank abound 8 seconds before starting and had the lean codes. Had 31 psi fuel pressure at idle, checked the specs and scratched my head at the ridiculously wide range they give. Searched online and many forums and determed that 60psi was the right pressure that year and engine. Replaced the pump assembly and it run perfect.
Always great information videos scanner
Another great video!
Thanks again.
@ranacherian Thank you for responding! That makes me feel much better
Yup. My 2000 Dakota R/T had those codes. I went through all the normal checks, replaced vacuum lines, replaced gaskets and now the fuel pump. I wanted to get all those easy less expensive things out of the way first.
thank you, got a clear idea of what's going on with my car
@Thor7167 Great catch friend! I found out after filming that the fuel filter had just been replaced, so it is definitely the pump.
A plugged filter would have a higher amperage, however unless you know what the exact amperage of fuel pump should be it is tough to ID. I have seen plugged filters have only minimal difference in amperage readings before and after. Some pumps have internal relief valves which will also affect the amperage readings.
Big fan of your videos!!!
i replaced the fpdm on my buddy's 04 f-150 it had the code "fuel pump driver module off line" me and my dad put it up on the hoist and the aluminum part of the fpdm was completely corroded. we took it apart after and found that water had got in and shorted a trace on the pcb to the ground plane. and now watching this i'm reassured it wasn't the fuel pump cause we didn't have the lean codes that this mercury had. Again thanks for all your videos man happy holidays!
very very useful video... keep it that way!
@amorozzo70 I think if you watch the videos right after the upload there is a sound quality issue until it is finished processing. Can you let me know if it is good now please?
@felplay vina there are mechanical poppet nozzels (mechanical injectors that are opened by fuel pressure) that will not open below 50 pounds of fuel pressure regardless of what the electrical injector part is doing
Either way is fine, just make sure you let me know when you put it up. Thanks Russ!
Hi im a tech at a shop now... im also the new kid and new to the business. Thank you for ur video.
Thanks man. I wish you could too.
Your welcome and thank you
thanks is corrected, thanks for replying
I LOVE YOUR VIDEOS.Would even probley pay for them(although keep doing this way :)
@ranacherian Can you double check the audio on your end please and let me know if it is fixed?
Thanks for sharing your knowledge
Nice review.
@supersport2778 I am not sure why, but set your video quality to 480p or less and it should be fine. I am using an HD camera but something must have changed with my settings. Thank you and let me know if this works.
@jdubb408 There are three main designs, mechanical return, mechanical returnless and electronic returnless (Section 14 in my book). Each one we treat a little differently, but on all designs fuel pressure should NEVER drop under load or during the snap throttle test. On the mech. return type with a vacuum reg. Idle psi is usually about 8-10 psi lower than WOT/.KOEO
@supersport2778 17:51 is the end of the video, sorry for the abrupt ending, I had some stuff I had to cut out at the end. It didn't change the final call though which was a bad fuel pump.
You have to be careful making a call based on amperage however a plugged filter will certainly cause a higher than normal reading. I think the best advice for these situations is to replace both pump and filter. You could replace the filter and re-test if you desire. However in my experience when a filter is plugged so bad as to cause low psi, you have already hurt the fuel pump. BTW the filter in the vid. was just replaced so bad pump only in this case.
I fitted a fuel pressure regulator (PR217 for an American Buick V6 or 5.3 litre V8) which is adjustable,meaning that the regulator had to be adjusted inside a bucket of fuel outside of the tank due to the regulator being fitted inside the tank in the Commodore.
The closest setting I got was 60 PSI of pressure adjustment & the fuel trim has come down to 8.59% on bank 1 & 9.38% on bank 2 which is a nice change from 25% on both.
thanks them are the same codes i just got.. and i watched some of you video and it showed me how to look at a couple of things and what to do to help narrow down the problem.. anyone who click thumbs downs is an ass and has never worked on vehicle in there life and needed help to figure out a problem. i got fords, kia and chevy but the codes are all about the same .. i make the same kind of video to help people.. and i get the same question from people.. my this is that is doing whatever, so what do you think lmao.. people come on we are not in front of you car its so hard to say what wrong with your stuff..these videos are to help point you in the right direction.. thanks for the video and info this should help me figure out moms kia
@ScannerDanner Thanks for the reply.
The car was warm when It came to me and the lady who owns it had to take it to go to work so I only had like less then two hours to look it over, she said she'll be back one day this week. I'm not sure about the MAP voltage yet. The fuel pressure was 44psi at idle and held after turning the car off.
I didn't think about the purge solenoid, I will check that when the car returns.
I will keep you updated when the car returns.
Thank you very much.
-Tim
4-6 on a typical PFI system and 8-10 on some higher psi systems (GM CPI for example runs 55-65 psi with this kind of amperage)
@jdubb408 Is this freeze frame data you are quoting? If so my next step would be to look at live data both STFT and LTFT at idle, 1500, 2500 rpm. Can you so this and give me the numbers?
that is because we had it running before that shot. what you were looking at was called "rest pressure". If we had just connected the gauge then yes it would have read zero and when he turned the key on it would have jumped up in psi.
Thank you sir paul!
Thank you!
yes that is correct, I think I use 4000-6000 as typical but it can go higher or lower than my spec and still be ok. Also fuel pump RPM isn't as important as pressure and volume delivery. Although a scope test of a fuel pump at times can be a very valuable test.
Especially with a dead commutator segment.
YOU ARE THE MAN
ScannerDanner doesn't check Mitchell...... Mitchell checks with ScannerDanner to confirm.
hahaha nice!
good video! congrats
@TRcustomengineering First, how does it run cold and at WOT? Are you sure the O2 is reporting accurately? If your not compare O2mv with tailpipe CO% and let me know how much CO is coming out of the tailpipe. What is your MAP voltage at idle and at 2000 rpm? How is the fuel pressure?(sucks to check on these if I remember right).
part 1: Nice video again. Fuel pump looks fine is actually very stable. Yes indeed Fuel pressure definitely low but talking about spec on that mountaineer I know for sure is 30-65 psi. Snap-on Verus is a nice generic scan tool but returnless old ford fuel system you have to consider also first of all to run KAM process. Then you must place the car in a dyno and run fuel pressure looking at FP% PID along with actual fuel pressure under 62% engine loads.
much respect
@victor35ma You are correct, it doesn't exist on this system. So it wouldn't be a Verus issue but a system design issue. Also, since this truck ran for 187,000 miles with the fuel lines that are on it, I would say line diameter should be fine, don't you?
The camera is a Panasonic HDC-TM60.
Had the same problem on my 1999 Ford ranger, v6 4.0. Turned out a weak fuel pump was throwing the codes.
Of course! Section 5 (under causes of a fixed rich O2 or negative fuel trim numbers)
thank you, so I am thinking on that fuel pump you have here on the demo if that pump is weak not enough fuel pressure you will have that one running at low rpm because amps is ok??
I heard of a formula to find out about the rpm if the fuel pump has 8 commuters I should set the cursor in between the 8 hump to get the delta time, the ms it took to complete the 8 hump divide 60.000/delta time = to rpm is that right ?? and most fuel pump runs at 3,000 to 6.000 rpm ??
I am having almost exact fuel trim patterns on my 2008 expedition 5.4L with both banks lean. Fuel pressure also decreases under throttle. It also has long cranks but only when it’s sat a long time.
When I turn the key on engine off, the fuel pressure reading is sporadic. Sometimes it will only load about 20 psi until repeated, sometimes it will go to 40…I don’t want to sink more cash into the car so I’m trying to be sure it’s a pump. I have already changed the filter.
More context if you’ve read this far…I’ve had issues with this car intermittently sputtering about once a month, I thought I fixed it with new plugs and then after that I got a CE light and discovered lean conditions.
SCANNERDANNER YOU ARE THE BEST ON EARTH, FULL OF 1OOO PERCENT KNOWLEDGE IN YOUR THOUGHTS. THE STATE OF CALIFORNIA IMPLEMENTED AN UPDATED
A REQUIREMENT FOR SMOG REPAIR TEST AND REPAIR FAILURE COURSES AND YOU ARE AHEAD IN YOUR TECHNICAL ABITITY. BLESS YOUR HEART AND YOUR FAMILY. THANK YOU, SIR.
i finally brought mine to the ford dealer. even though my airflows on my mass air where normal looking. my baro frequency was in the 140's and im at 750ft elevation. so my computer thought i was at 4000 feet elevation. running 7 to 10 percent long term fuel trim. and my engine was pinging despite the knock sensor retarding it. i would get as high as 49 degrees advance off idle no load. and thats when it has a miss to it.my sensor is clean too. the baro readin is soo important on fords
It's just me but I like to see things diagnosed to the end. Fuel pump vs. fuel filter vs. fuel pressure regulator (if not built into the pump--you did say that the regulator on this vehicle is in the tank). I believe that the fuel filter should be changed anyway and first to see if that fixes the problem.
@ScannerDanner I would say it is not a ford issue because I am able to meter this FP % pid on old returnless ford fuel system using OEM ford diagnostic tool. the PID for late model is: FRP% FRP# FRP which stand for fuel rail pressure supported by a FP sensors (tranducers).
I will get that camera. thanks for your videos. you are doiing a great job
hi. Paul nice video I am wondering what is the average amps I would expect from good working fuel pump? thanks
good video smart guy
wait, are these negative or positive fuel trim numbers
@TRcustomengineering Oh and make sure the purge solenoid vacuum hoses are not reversed (if its possible)
Hi Paul I do have question about fuel pressure, 02 gm Yukon no codes symptoms starter only when I push the accelerator. Fuel pressure 50 lb, when it should be 60 to 65, with 50 lb low why it won't start up?
My 99 Expedition 5.4 was reading 0 even with the switch and engine not running and then as soon as I started the engine the pressure went up to 31 psi and then it would jump up to about 38 when hitting the throttle. It stalled on me at a red light and sometimes it wont start in the mornings.
98 expl v6 sohc has two lines 7:30 so it has the vacuum difference range at idle and WOpen.
[Idle psi is usually about 8-10 psi lower than WOT/.KOEO]
So it is running lean only under load. That is typically from low fuel psi or a dirty MAF sensor. But your honda is a MAP engine I believe so that rules out a MAF problem. Make sure your MAP is reading around 2.8v at WOT/KOEO. A test drive with a fuel psi gauge taped to the windshield may be in order, but be very careful and take a fire extinguisher with you. Was there any debris in the fuel tank when you changed the pump? (water, rust etc.) If so your injectors may be plugged
hi ScannerDanner good video l have 97 ford expedition 5.4 l have p0171&p0174 & did smoke tester no leaks on the intake so far so I am .going to replaced fuel regulator & maybe like you said fuel issues thanks so much
+Oscar Alarcon check the MAF next
+ScannerDanner hii there i have a 07 ford expedition 5.4 wit 02s11 02s12 stuck rich
Thanks for that. I'm currently dealing with a suspect pressure reg on a 2011 vx zafira at work. The waveform is all over the place. My next step was to check the fuel pressure with a gauge, it would jump to around 2 bar KOEO then drop to zero. Cranking would see the pressure steadily rise to 2.8 bar before spluttering into life. Compared to another vehicle and it was showing 4 bar KOEO and KOER. Can post the waveforms on the pico forum tomorrow if you want to take a look?
How do you figure out what BARO hz calculation is adequate for each vehicle make and model?
Is it possible to take the fuel injectors out and clean the inside of them?
Thank you Paul for fast reply. Map is new. I swapped injectors and FPR from the donor car and no change (maybe a little more power). Fuel tank was clean as new and pump's outer filter was very clean. Will look into fuel pressure under speed as you said and a MAP signal. *Just to make sure: ground voltage drop test showed just a little bit above normal level (>0.5v) 0.53-0.55v, can it affect pump that bad ?
What program are u using on your lap top?. It works with your Pico amp probe?
all of the returnless fuel systems will show a brief sudden drop on a snap throttle test. especially the electronic ones with no regulator. as long as it recovers quickly you're ok
part 2: I am not sure if you can see that PID using Verus live data before 2004 since we never use Verus to troubleshoot Ford. Also for that very vehicle there is a recall on fuel pressure line diameter so, make sure you got the upgrade
What kind of camera are you using to get those nice HD videos? I will get one. Gracias de Nuevo.
Will a dirty maf also cause ring clatter under load?
Hi paul. Would a volume test identify if its a filter problem on this system? Or getting low wolume wouldnt confirm that it is a filter or pump problem?
I agree, someone should call them and tell them to hook me up :-)
it does but it is more generalized and not vehicle specific. of course I give specific examples of what we're looking for with certain sensors but you cannot apply that across the board. fill out your name and email on my webpage and I'll send you some more information on it. thank you for your interest!
@ScannerDanner In fact just a simple multimeter would have been good for this test. I really wasn't concerned about detail as much as what was the overall amperage.
I've ran into that problem at least a dozen time on those explorers
hi, Paul. Great video. I have Honda Civic 1998 DX. Getting occasional P0171 (lean) whenever LTFT limit maxes out. STFT range at idle [ - 2.77 ~ + 3.00 ]. Upon acceleration STFT numbers plummet : 30 mph - 24%, 50 mph - 35%, 60-70 mph - 49% ( flat line on scan tool ). Once pedal released numbers drop to flat 0. Things done: new fuel filter, fuel pressure within specs (at idle) and open throttle (parked), swapped fuel pump, swapped ECU, voltage drop test on pump's power feed and ground (parked), ?
Hi mister Danner. Can a high fuel pump pressure greater then normal cause a rich condition?? Thanks.
😅Thanks bro
I have a 2006 highlander hybrid with a VCS Trac off check engine and brake light on any thoughts
Hiya Paul ,
Wouldn't voltage drop to the pump, across the relay cause similar amp readings you were getting??
Wait, what? Refresh my memory please :)
As for the engine load data PID, I simply look at it for determining type of lean condition. If you have my book I have some case studies on that. To much detail to put here in a limited character box, sorry. In short, if lean condition is at idle = vacuum leak, if lean condition is under load = dirty MAF, low fuel pressure
Hi a had a situation that reminded me of this video. i replaced a fuel pump (along with a filter,) to solve a no start condition on a 04 E250 with a 4.6L returnless fuel system. as part of the diagnosis i used an IDS scan tool to graph FRP vs. TPv under snap throttle and it dropped about 10 psi. (engine ran briefly when the pump began working again.) after the repair i redid the test to verify. it still dropped 5-6psi, then surged and finally stabilized. any thouhgts why pressure still dropped?
Hiya Paul wouldn't the amperage be silimlar if there was a voltage drop to the pump, say for instance across the relay??
i know at my BMW dealership we check the fuel pressure from the tank pump, usually around 450 kpa, and if that is good but the vehicle still has fuel codes we do a high pressure pump- but only cause theyre a common issue. im sure you could also look up fuel pressure by looking at sensor read outs on a verus or diagnostic machine, but ive never had to do that yet.
Thanks Russ, I just read your email, I'll get back to you soon, very busy right now
If i have to snap the throttle fast 3 t o4 times and pressure drops 4 psi on a returnless system is that bad as well? my system calls for 58 psi plus or minus 5 and the highest I get is 49 psi. Would that cause a p0171?
Hi Paul,
I have a question for you.
I'm having a real hard time diagnosing a 02 chevy cavalier that the customer bought from a dealer that had put a used 03 pontiac sunfire engine in it.
The car is running rich (LTFT is -14.1) with no check engine light on, and the car will surge
up and down and want to stall after letting off the gas when it come back down to idle.
The o2 is always around 0.800V at idle.
Do you have any idea's or tips for me?
Thanks,
-Tim
I have a 99 ram 5.9l gas motor. my fuel trim is 50psi kinda shaky. haines manual says should be between 35 to 45 psi. a 5 psi isn't un cormmon. havent done a snap throttle like I shouldve....... lol what would bad single line fuel line with a bad regulator look like on the guage?
Thanks for all your help with my 01 silverado. I've come to conclusion that i do have a fuel delivery issue. Its kinda baffling because after going through and checking all grounds i could find,cleaning the map sensor and egr valve looking at every connector for any obvious signs of trouble i have finally got my truck to run pretty good. Idles smoother and the intermittent misfire is gone. When i get on the Hi way and mat it the truck goes like a bat out of hell. I do notice a slight drop off around 80 or 90 though but is much better than before. However, my fuel trims are still out of the park. At idle im seeing upwards of between 30 and 40 % on short term and long terms steady at 25% on both banks. Im thinking the fuel pump is just not push enough fuel for computer to make corrections. If i wasn't see this on scan tool i wouldnt think there was a problem at all. No check engine lite on either
I should see around 55 to 60 psi on fuel pressure test on this 6.0 vortec correct?
cranking it should be 60 psi all day.
Your trim numbers are very positive at idle. (possible vacuum leak) What do they look like at 3000 rpm in park, with no accessory loads, steady throttle?
ScannerDanner fuel pump shat the bed today. At least thats what i think. Have to get it home and check it out. I'll let you know what i find. Ive been hunting chassis ground and cleaning them as i find them but havent crawled under truck yet. I'll get to that after i fix hot hard start on my buddies 69 road runner and carb issue on his old honda xl dp bike. Busy busy thats me. Thanks for all your help mr. Danner. You're the best. Holler at you soon friend. By the way does the abs/brake light issue on this truck share any common ground? Like mutual ground point locations do you know. These lights been coming on more frequently lately too
Not sure man. I'd have to look at a diagram. We can do that on my forum. It's free to join.
www.scannerdanner.com/forum/post-your-repair-questions-here.html
@@ScannerDanner
I have an 04 GMC Yukon, 5.3. Showing lean bank 1& 2, truck starts and idles great. But under load has an intermediate problem. When it does it 40mph is a stretch for it. It’s quite dangerous. Like u may pull up to a red light go to pull out n hope n pray you don’t get ran over. U can be driving 30 mins on highway doing great but all of a sudden it hesitates and you pray to make it back home. U can feel it hesitate, let off the fuel a little and it will go on but not if you push it. If u push it, it will get worse and basically go into limp mode or reduced power mode. Fuel pressure test shows 53 psi at start up and idle, 45 psi at 3000 rpms, 40 at 4000 and from 5000 to rev limiter it falls to about 30 lbs. under snap throttle test.
40 mph and below 2000-2500 rpms Seems to be the sweet spot were it will run but if u push it at all it hesitates, new acdelco fuel pump in July, fuel filter is built into pump, New Delphi maf in dec, new acdelco spark plugs n wires in oct. I did a fuel treatment and c-foam through throttle body and vac line, this past weekend which straighten it up for a couple days but it came right back, same as it did with all these parts I’ve listed. This thing has me puzzled. Been told fuel regulator but for the life of me I can’t find one on these fuel rails, been told fuel filter but this one is built into tank within pump housing. Here lately it’s been a coin flip on getting from home to work and back the 7 min drive each way. At lunch today it took 20 mins to make that 7min trip cause it was acting up so bad. It seems worse if it gets hotter, I can clear codes and drive 40 mph home 45 mins and it still hesitates if u push too hard but codes won’t come back for a day or two. I almost know it’s a fuel delivery problem just from the codes and what I’m seeing driving it. The fact it’s 2500 or 2000 rpms at 40 mph
But idk what to turn too next, I’m kinda stuck waiting for my new scan tool to come in to see the live data, n freeze frame data. I’ve always been the go fuel pumps are either dead or good no in between but this one has me rethinking that stance. But also thinking regulator if I could find one on it, or a fuel line restriction.
I measure the fuel pump pressure by bar and I find usually the pressure must be between 6 to 8 bar , I wonder are it right or not ?
thank you very much.
I had a E-150 with 2 fuel pumps-the low pressure pump (~3 psi) is in the tank and the high pressure is inline. You need two gauges since most gauges capable of reading the high pressure will not accurately indicate 3 psi. Some vacuum gauges can also read low psi fuel. If you have low psi, the high pressure boost pump is faulty. If you have 0 psi, the low pressure pump is faulty--the boost pump is not getting any gas. (Given that only one pump is bad and that the regulator and filter are good.)
Hey, so if I'm aiming for a weak fuel pump on a car, should revving it up to 3k rpm while it's stationary cause the LT to rise 20+%? My roommate's fuel trim goes up during acceleration on the road (up to about 24% by the time you're at 50mph) but if I rev it while the car is stopped, it stays down at normal levels of about 0-4%. Idle speed trims are also 0-4%
I already ruled out MAF through both cleaning and swapping the good compatible MAF from my car to hers, and she has 2 newer OEM A/F / O2 sensors.
There's really no drivability problems here, just the leaning out while driving, and I'm thinking this might be why her catalyst monitor is never triggering ready no matter how many times I do the driving parameters to make it ready (coolant temp, IAT, etc all in order). Never throws a P0420 either though.
Hey paul, looking for some help here. I went through some water a few weeks ago. When I got home I checked my air filter and it was soaked. Replaced air filter and dried everything up. The next day a p0174 code came on. Truck runs fine still so I just cleaned my MAF.....no luck. So I have already changed the MAF and both right bank O2 sensors. SES light is still on. Any thoughts? Pulled the freeze frame data today if this helps anyone take a guess on whats causing this.
Load value-88.24%
Coolant temp-186.8
STFT B1-7.81%
LTFT B1-33.59%
STFT B2-8.59%
LTFT B2-33.59%
RPM-2062
Vehicle Speed-77.05mph
I have a ford focus mk2, European version and it doesn't have a MAF sensor. Could p0171 he generated because of the swirl flaps that have gone bad?
@94vettelover2 haha I will don't worry. You could buy my book though if you like:)
At 7:21 the begining of the fuel pressure test the gauge was already reading 33psi it never change when you turn the key to the ON position and back to the OFF position yet your student said it flickerd...Was the gauge suppose to read 0 (zero) before you turn the key to the ON position? Please explain Thank you.
Sure! What type of fuel delivery is it? Electronic returnless, mechanical returnless or mechanical return type? Also is it possible you could send me the FP wiring diagram? I don't have access to that vehicle nor have I ever even heard of one :)
Refresh the page.There is nothing wrong with the video thanks!
ok, so in this video the fuel pump failed because the pressure dropped 10psi and didnt surge? and struggled to reach dynamic pressure after startup?
Just here watching videos but my Acura does get the p0171 at idle when it sits for 10-15 mins I turn the car off and then start the car 5 mins later. I had my scanner hooked up and the freeze came said the intake temp was 139 but this is probably heat soaked from sitting but it’s 40 degrees outside. During the summer if I sit with the ac on it doesn’t happen. Come to think of it I just changed the purge solenoid last week and it’s more apparent now with the 0171 and 0174 codes. I do have a very small exhaust leak due to a gasket but it’s been leaking this entire time I’m sure if it and the code didn’t show up.
If the exhaust leak is near the O2 sensor or upstream of the O2 sensor. Fix the exhaust leak first!