Try to run a larger regulator after the injection with a larger return side.. I think part of the problem is the fuel pump has to much volume and when you restrict it to much the pump cant move the fuel and it start to cavatate....it is trying to pump the same fuel over and over creating air that's why it is not as bad under wide open throttle you have more fuel volume
Cavitation is coming from your ball valve in your bench test (ball valves are never designed to be throttled), and coming from your bypass regulator in your Jeep application. You need a regulator with a larger flow capacity; as to say, a larger needle and seat. I have a Holley reg with a 3/8" ball and 5/16" seat. You need a smooth transition from high to lower pressure. If your bypass regulator is an aftermarket replacement type, it might lack in flow. Try a performance (larger flow rated) regulator and I think you will solve the problem. --Doozer
You can try a check valve before your pump usuaally at the end of the hose to help keep pressure stable. also you have too much negitive pressure before the pump because it sucking fuel up from the bucket.when it comes to external pumps they need to be mounted below tank level so it can be gravity fed which would increase pressure on the back side of the pump in turn , less chance of cavitation due to the positive pressure to the pump.
From what I know from being a heave equipment mechanic and working with hydraulics I would say the bubbles are coming from the psi regulator. I would suggest running a larger diameter fuel line line from tank to injector. You may have to change you pump also. I also don't think your regulator is capable of the amount of volume trying to pass through. You can run the regulator anywhere down stream from the pump because of Pascal's law that psi is equal at all points. So when you step on the throttle you drop manifold vacuum to the regulator in return raising the fuel psi to whatever the max relief is in the system supplying more fuel to the injectors. Basically blocking off the return to tank. Some things I think you should look at are 1. What is the max psi in the system? 2. What is the flow/volume of the pump? This will most likely very. 3. What is regulator capable of volume wise? 4. What is the volume of required for the injectors? 5. What should system psi be at idle and with the regulator closed? (WOT). Sorry for the long rant but talking things throw is how I figure things out. I hope it helps.
Wonder if it's a pump problem at all ... I'd guess there is a high/low pressure change at the regulator allowing stored oxygen in the fuel to come out. Be interested to see a clear line from the pump to the regulator, and see if bubbles originate in the regulator. Could also try putting the regulator AFTER the fuel rail.
It's related to the clearance between the impeller and stater in the pump Try positive displacement roller fuel pump off 1979-81 Toyota Supra or 80 to 85 Cressida
Wonder if this problem is less likely with a in tank pump. Do you have a fuel injected tank laying around with a pump in it you could bench test like your bench test your doing here?
Given the pump does not have cavitation at low pressure but does at higher pressure is very telling. The pump may be over pressurizing for what it is made for. This would be that the pump at higher pressure has fluid going around the vanes at a velocity that causes air to separate from the fluid (cavitation). Fluid going around impellers due to over pressure or wear has a much higher flow rate than what is within the out-port flow and would change with type of fluid being pumped. With water this would be at around 10 ft per second if I remember right. Water pumps with cavitation will actually wear out an impeller. I have seen bronze impellers that were worn to a high polish. May want to look for a pump that is rated at a higher pressure or higher quality at the ratted pressure. Just thought of something, pressure within pump impellers are a closed system (they do not know what the pressure is outside of pump) so you may be able to put a medium pressure pump in before or instead of the low pressure pump. This would lower the pressure deferential between the high and low side of the high pressure pump.
The fact that you appear to have good flow with no air until you make the pump work hard tells me that you have a damaged pump. Same thing with pump number two. So go out back and get an old ford pickup pump out of its framerail and mount it in the jeep as low and as close to the tank as possible. These pumps are not made to pull but to push. Then when you get that all straightened out, take it out on the trail but do not run it out of gas because that kills pumps.
In the Jeep it shouldn't be pulling up. Plus he has the other tank above his main tank. So shouldn't that make a small amount of positive pressure? And ain't the old ford pumps Bosch fuel pumps?
@@shaunadams3170 Yes the top tank would reduce the lift the pump has to overcome as long as it has fuel in it. The only time I have seen lift be a problem is when the guy had the pump mounted high in the engine compartment and a rear mounted tank so when he stood it on end it had eight feet of lift.
I get enough air in the fuel line that i can put a plastic bag over the EFI body and starve it for air and the motor still runs? I put the in tank hollykit and it's a little better.
I would check the tank fuel is drawn from u said u had two and see if there is a fuel slosh issue or bad return line drawing air pumping it into the lower tank. The fuel pump lol idk could use attention.. i would get a efi one for an ls like this Walbro GSL392 maybe smaller these r 70 bucks mean for a efi swap common w ls motors.. with 45-75 running pressure a cheap return style regulator and if u got the same issue the problem is in the tank or lines but i would look into the tank and fuel slosh cause once air is in the gas its going to flow back to the pump not float out right away? Idk
It's in that ballpark, yes. It is also part of the TBI system (built into the casting and there is a replaceable diaphragm) so it can't just be swapped in here.
Fuel pressure regulator on your fuel rail . The only way air can get in at low speed is you have tiny leak in ether your pump housing or your lines some where pulling air. I wonder if the pump has like a waist gate that ant closing at low pressure
Hopefully you figured out, but looks to me there is too much restriction going to the pump. For the pump to push the fuel at that pressure its creating a low pressure point right at or behind the propeller for pulling the fuel. Low pressure means a lower boiling point which means easier to create cavitation. Which to me is what you’re seeing. A possible fix is to use a bigger hose going to the pump or figure out some other method to get the fuel to the pump in greater volume. Also, once you start getting cavitation it can very quickly damage the pump. You might need a new pump as well. Another solution is try a different pump design. In-tank pumps can work better because the fuel is right there.
What if the feed line was straight to the rail and the regulator was on the other end of the rail with the return exited from the regulator? Now I have to build me a setup to play with . Thanks for the brain teaser.
You must make sure your fuel source is placed well above your fuel pump. The tank to pump intake line should be of slightly larger diameter than the outlet line. Never ever place a full size fuel filter between the tank and the pump.... I've been there... If pressure and flow are an issue, consider several staged pumps and a swirl pot.
Drag racers run external fuel all the time. Either they have a better pump or a different regulating system. I woul think you would need to regulate the fuel psi at the engine for the injectors and then reduce the size of the fuel return line so that it acts as a restriction to prevent air. What I did not see is the pump turning off once a preset pressure was achieved. It's the inability of the pump to vary fuel flow and stabilize pressure that is your problem.
Maybe, but it is doing it on the bench in cold condition, too. I assume the pump he is using is an online, not in-tank unit. If it is in-tank, it is designed to be cooled by the fuel immersion, so you may have a point.
So could you regulate the voltage to the pump to prevent the boiling and adjust the regulator to still feed the proper rail pressure? Are use the fuel filter that has the return line nipple made on it?
@@shaunadams3170 then you'll have to have a computer to vary the voltage to the pump IAW ROM. Way too complex, and this is a carb we are talking about, not a moon shot.
Try to run a larger regulator after the injection with a larger return side.. I think part of the problem is the fuel pump has to much volume and when you restrict it to much the pump cant move the fuel and it start to cavatate....it is trying to pump the same fuel over and over creating air that's why it is not as bad under wide open throttle you have more fuel volume
Cavitation is coming from your ball valve in your bench test (ball valves are never designed to be throttled), and coming from your bypass regulator in your Jeep application. You need a regulator with a larger flow capacity; as to say, a larger needle and seat. I have a Holley reg with a 3/8" ball and 5/16" seat. You need a smooth transition from high to lower pressure. If your bypass regulator is an aftermarket replacement type, it might lack in flow. Try a performance (larger flow rated) regulator and I think you will solve the problem. --Doozer
You can try a check valve before your pump usuaally at the end of the hose to help keep pressure stable. also you have too much negitive pressure before the pump because it sucking fuel up from the bucket.when it comes to external pumps they need to be mounted below tank level so it can be gravity fed which would increase pressure on the back side of the pump in turn , less chance of cavitation due to the positive pressure to the pump.
Put it below fuel level with a large fuel feed
Hope ya get it sorted out.
Can't wait to see Super-Jeep back in action soon. 😎
We have a similar problem on 22r toy trucks we install a carburator fuel filtet in line of return line to slow the return took care the problem
This sounds a lot like what my TBI 5.7 I swapped into my S10 is doing. This bears further investigation, thank you!
good to see you back
Good to know your still kicking Carl 👍
From what I know from being a heave equipment mechanic and working with hydraulics I would say the bubbles are coming from the psi regulator. I would suggest running a larger diameter fuel line line from tank to injector. You may have to change you pump also. I also don't think your regulator is capable of the amount of volume trying to pass through. You can run the regulator anywhere down stream from the pump because of Pascal's law that psi is equal at all points. So when you step on the throttle you drop manifold vacuum to the regulator in return raising the fuel psi to whatever the max relief is in the system supplying more fuel to the injectors. Basically blocking off the return to tank. Some things I think you should look at are 1. What is the max psi in the system? 2. What is the flow/volume of the pump? This will most likely very. 3. What is regulator capable of volume wise? 4. What is the volume of required for the injectors? 5. What should system psi be at idle and with the regulator closed? (WOT). Sorry for the long rant but talking things throw is how I figure things out. I hope it helps.
Wonder if it's a pump problem at all ... I'd guess there is a high/low pressure change at the regulator allowing stored oxygen in the fuel to come out. Be interested to see a clear line from the pump to the regulator, and see if bubbles originate in the regulator. Could also try putting the regulator AFTER the fuel rail.
It's related to the clearance between the impeller and stater in the pump
Try positive displacement roller fuel pump off 1979-81 Toyota Supra or 80 to 85 Cressida
Wonder if this problem is less likely with a in tank pump. Do you have a fuel injected tank laying around with a pump in it you could bench test like your bench test your doing here?
Given the pump does not have cavitation at low pressure but does at higher pressure is very telling. The pump may be over pressurizing for what it is made for. This would be that the pump at higher pressure has fluid going around the vanes at a velocity that causes air to separate from the fluid (cavitation). Fluid going around impellers due to over pressure or wear has a much higher flow rate than what is within the out-port flow and would change with type of fluid being pumped. With water this would be at around 10 ft per second if I remember right. Water pumps with cavitation will actually wear out an impeller. I have seen bronze impellers that were worn to a high polish. May want to look for a pump that is rated at a higher pressure or higher quality at the ratted pressure. Just thought of something, pressure within pump impellers are a closed system (they do not know what the pressure is outside of pump) so you may be able to put a medium pressure pump in before or instead of the low pressure pump. This would lower the pressure deferential between the high and low side of the high pressure pump.
The fact that you appear to have good flow with no air until you make the pump work hard tells me that you have a damaged pump. Same thing with pump number two. So go out back and get an old ford pickup pump out of its framerail and mount it in the jeep as low and as close to the tank as possible. These pumps are not made to pull but to push. Then when you get that all straightened out, take it out on the trail but do not run it out of gas because that kills pumps.
In the Jeep it shouldn't be pulling up. Plus he has the other tank above his main tank. So shouldn't that make a small amount of positive pressure? And ain't the old ford pumps Bosch fuel pumps?
@@shaunadams3170 Yes the top tank would reduce the lift the pump has to overcome as long as it has fuel in it. The only time I have seen lift be a problem is when the guy had the pump mounted high in the engine compartment and a rear mounted tank so when he stood it on end it had eight feet of lift.
I get enough air in the fuel line that i can put a plastic bag over the EFI body and starve it for air and the motor still runs? I put the in tank hollykit and it's a little better.
What have you found on this? What size are the feed and return lines?
is the return line just dumping into the fuel cell above the fuel level? it should be returned into the tank below the fuel level.
I would check the tank fuel is drawn from u said u had two and see if there is a fuel slosh issue or bad return line drawing air pumping it into the lower tank. The fuel pump lol idk could use attention.. i would get a efi one for an ls like this Walbro GSL392 maybe smaller these r 70 bucks mean for a efi swap common w ls motors.. with 45-75 running pressure a cheap return style regulator and if u got the same issue the problem is in the tank or lines but i would look into the tank and fuel slosh cause once air is in the gas its going to flow back to the pump not float out right away? Idk
Couldn't be fuel slosh because it's doing it seating still.
@@shaunadams3170 correct. And can't be a return leak because it's doing it on the bench.
Does the factory TBI use a pressure regulator for 12 psi? Maybe try & running it with just the low volume pump? 12psi seems pretty low?
It's in that ballpark, yes. It is also part of the TBI system (built into the casting and there is a replaceable diaphragm) so it can't just be swapped in here.
Fuel pressure regulator on your fuel rail . The only way air can get in at low speed is you have tiny leak in ether your pump housing or your lines some where pulling air. I wonder if the pump has like a waist gate that ant closing at low pressure
all cars on the road today have a in tank pump
Hopefully you figured out, but looks to me there is too much restriction going to the pump. For the pump to push the fuel at that pressure its creating a low pressure point right at or behind the propeller for pulling the fuel. Low pressure means a lower boiling point which means easier to create cavitation. Which to me is what you’re seeing. A possible fix is to use a bigger hose going to the pump or figure out some other method to get the fuel to the pump in greater volume. Also, once you start getting cavitation it can very quickly damage the pump. You might need a new pump as well. Another solution is try a different pump design. In-tank pumps can work better because the fuel is right there.
What if the feed line was straight to the rail and the regulator was on the other end of the rail with the return exited from the regulator? Now I have to build me a setup to play with . Thanks for the brain teaser.
Good idea
Thats the correct way to do it for a rig with 8 injectors with a tbi you have to regulate the pressure first so i wont run rich
You must make sure your fuel source is placed well above your fuel pump. The tank to pump intake line should be of slightly larger diameter than the outlet line. Never ever place a full size fuel filter between the tank and the pump.... I've been there... If pressure and flow are an issue, consider several staged pumps and a swirl pot.
Drag racers run external fuel all the time. Either they have a better pump or a different regulating system. I woul think you would need to regulate the fuel psi at the engine for the injectors and then reduce the size of the fuel return line so that it acts as a restriction to prevent air. What I did not see is the pump turning off once a preset pressure was achieved. It's the inability of the pump to vary fuel flow and stabilize pressure that is your problem.
... Or they are, you know, going WOT for 12 seconds at a time, and use fuel chillers.
Try dropping the fuel line size.
if you are building up and bleeding off while running like you say it sounds more like a fuel boiling problem to me
Maybe, but it is doing it on the bench in cold condition, too.
I assume the pump he is using is an online, not in-tank unit. If it is in-tank, it is designed to be cooled by the fuel immersion, so you may have a point.
So could you regulate the voltage to the pump to prevent the boiling and adjust the regulator to still feed the proper rail pressure? Are use the fuel filter that has the return line nipple made on it?
@@shaunadams3170 then you'll have to have a computer to vary the voltage to the pump IAW ROM. Way too complex, and this is a carb we are talking about, not a moon shot.
Put a FASS
Also thats the reason toyota uses a fuel damper on the rail
Есть ето из России?!
I think that says, "it's because it's not Russian"... Didn't even Google it.
So what if the fuel pressure regulator is causing cavitation I wood bypass it and see what happens.
What will happen is the vehicle will run pig-rich and like crap. Quite likely get fuel wash in the oil and wipe out the journals, too. HORRIBLE idea.
Nothing will happen if you run it for a minute or two just to test it.