Fuel Pumps, Fuel Pressure, and Frustration

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ironwill11
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Fuel Pumps, Fuel Pressure, and Frustration

Post by ironwill11 »

Does anyone have any experience with an out of take, electric, in-line, TBI fuel pump? I have had one of these for 15 years and it always worked fine for me. I hooked up an electric fuel pressure gauge and for the most part is it pretty constant at 13psi. I have noticed that the longer it is running (when it warms up it will drop down to 12 psi and then sometimes flicker between 11 and 12 psi. I have a GM TBI unit on my 4.3l and replaced the stock fuel pressure regulator with an adjustable one. I always thought that the fuel pressure should stay rock solid on the the same psi all the time. I can't help but wonder if my fuel pump is going or if the electric gauge is just not that good.

Does anyone have experience with either the electric fuel pump gauge or the electric, in-line, TBI fuel pump?

It is really frustrating when trying to tune.

Will
billr
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by billr »

Do you know the specific brand and P/N or the pump? Pumps in general are either positive-displacement (PD) or "kinetic", and fuel pumps are no different. Some are PD, with gears, rollers, vanes, or pistons to move the fuel. Kinetic are usually referred to as centrifugal or turbine pumps and have just and impeller. Fuel pumps come both ways, sometimes both ways even for a specific OEM application. Some ( I have opened one) even have both PD and turbine in the same pump, the kinetic "charges" the PD section.

So, finding out what type yours is will help, and I don't think you want to take it apart to find out. One quick test is to connect only a gauge to the pump output port, so there can be no flow, and then powering the pump. If it is PD, and good, the pressure should shoot up high, like to 100 psi or more, and probably stall the pump motor as pressure gets high. If pressure stays low, in that 10-20 psi range, then it may be a kinetic pump, or may be a very tired PD. If you have a way to vary voltage to the rpm, thus varying the pump rpm, then that "dead-head" pressure should vary with the rpm. A check-valve in the pump outlet may influence that pressure vs. rpm relationship, but I guessing there will be enough (slight) leakage through an old check-valve that it won't be an issue. See how fast pressure decays when the power is removed to see if that check-valve is a problem for doing that psi/rpm test.
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by turbo conversion »

How old is the pump and when is the last time you changed the fuel filter?

Also when the fuel pressure drops does the afr go lean?

David
1976 Datsun 280Z L28ET Garrett GT35R T3-T04E stage3 50 trim 63 A/R housing custom grind cam 2000-6000 rpm 440cc injectors intercooled 18 lbs. boost
3" exhaust turbo back LC-1 o2 sensor Hallman manual boost controller EDIS 6 ignition batch fire 60mm throttle body 5 spd T5 borg warner 3.54 lsd
ironwill11
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by ironwill11 »

billr wrote:Do you know the specific brand and P/N or the pump? Pumps in general are either positive-displacement (PD) or "kinetic", and fuel pumps are no different. Some are PD, with gears, rollers, vanes, or pistons to move the fuel. Kinetic are usually referred to as centrifugal or turbine pumps and have just and impeller. Fuel pumps come both ways, sometimes both ways even for a specific OEM application. Some ( I have opened one) even have both PD and turbine in the same pump, the kinetic "charges" the PD section.

So, finding out what type yours is will help, and I don't think you want to take it apart to find out. One quick test is to connect only a gauge to the pump output port, so there can be no flow, and then powering the pump. If it is PD, and good, the pressure should shoot up high, like to 100 psi or more, and probably stall the pump motor as pressure gets high. If pressure stays low, in that 10-20 psi range, then it may be a kinetic pump, or may be a very tired PD. If you have a way to vary voltage to the rpm, thus varying the pump rpm, then that "dead-head" pressure should vary with the rpm. A check-valve in the pump outlet may influence that pressure vs. rpm relationship, but I guessing there will be enough (slight) leakage through an old check-valve that it won't be an issue. See how fast pressure decays when the power is removed to see if that check-valve is a problem for doing that psi/rpm test.
I have looked all over the pump, but there is no name on it anyore. It is 15 years old. I took a video of the issue I am talking about and will be posting the link to youtube as soon as it loads. I will have to take off the pump to test it.

Will
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by ironwill11 »

turbo conversion wrote:How old is the pump and when is the last time you changed the fuel filter?

Also when the fuel pressure drops does the afr go lean?

David

The pump is 15 years old, I cleaned out the fuel filter leading into the the throttle body. It was a glass one that comes apart (I know I know, I should not have that there - my dad put it in a very long time ago and I can't bring myself to take it out - plus I like being able to see the fuel before it goes into the throttle body).
The fuel pressure does vary slightly during warm up; however, the idle is still high and there is not a lot changing afr. That being said, it did do it after being warmed up and the it is hard to pin down the afr. I would say if it does, it only does a little. It was the difference of between 13.2-13.4 to 13.5-13.7. This was with a change in pressure between 13 psi to 12 psi (it was going back and forth between the two) (the pressure starts at 14 psi during warm up and eventually comes down to 13 during warm up. I have a video of the psi jumping around ill be posting on youtube.

Will
billr
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by billr »

Did you ever check what pressure the pump can do "dead-headed"? If that is much over the 13 psi you are looking for, say 20 psi or better, then any poor regulation has to be an FPR problem. Yes, you may need to check that "dead-heading" after the pump has been running for a while, and maybe even check FP with fuel flowing (but not past the FPR). However, I don't think that few tenths of a psi is your root problem. My experimenting has shown that injector flow is rather insensitive to FP, it is far from a linear change. There is an FP vs. flow conversion formula in a recent thread, take a peek at that.
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by turbo conversion »

Me personally, I would replace a 15 year old pump and go from there.

Also if I remember correctly there is a filter in the GM throttle body, it may be dirty.

David
1976 Datsun 280Z L28ET Garrett GT35R T3-T04E stage3 50 trim 63 A/R housing custom grind cam 2000-6000 rpm 440cc injectors intercooled 18 lbs. boost
3" exhaust turbo back LC-1 o2 sensor Hallman manual boost controller EDIS 6 ignition batch fire 60mm throttle body 5 spd T5 borg warner 3.54 lsd
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by DaveEFI »

turbo conversion wrote:Me personally, I would replace a 15 year old pump and go from there.

Also if I remember correctly there is a filter in the GM throttle body, it may be dirty.

David
Not sure it's ever a good idea to simply throw new parts at a problem, without identifying what the fault is first.
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turbo conversion
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by turbo conversion »

There is no way a 15 year old pump can be at peak performance, just saying.

David
1976 Datsun 280Z L28ET Garrett GT35R T3-T04E stage3 50 trim 63 A/R housing custom grind cam 2000-6000 rpm 440cc injectors intercooled 18 lbs. boost
3" exhaust turbo back LC-1 o2 sensor Hallman manual boost controller EDIS 6 ignition batch fire 60mm throttle body 5 spd T5 borg warner 3.54 lsd
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by kjones6039 »

turbo conversion wrote:There is no way a 15 year old pump can be at peak performance.........
Boy, howdy!!

Ken
1979 Corvette - 383 CID SBC w/ Holley Pro-Jection 900 CFM TBI, 4-85 lb lo-z injectors & Walbro 255 pump
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by billr »

Still, my pump is over 40 years old (and was sick when I got it) but will send the rail from 0 to 3 bar in less than a second. It all depends on the design of the pump and what excess capacity it has for the application.

Mechanical FPRs are not, I think, precision control devices. Getting better than 1/2 psi regulation is not a realistic expectation.
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by turbo conversion »

Not looking for an argument, just saying what I would do.

David

EDIT: what car do you have that has a 40 year old pump in it?
1976 Datsun 280Z L28ET Garrett GT35R T3-T04E stage3 50 trim 63 A/R housing custom grind cam 2000-6000 rpm 440cc injectors intercooled 18 lbs. boost
3" exhaust turbo back LC-1 o2 sensor Hallman manual boost controller EDIS 6 ignition batch fire 60mm throttle body 5 spd T5 borg warner 3.54 lsd
slow_hemi6
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by slow_hemi6 »

It really is hard to get a steady needle indication on a fuel line that has the injectors hammering away at it. Touch the lines and what do you feel. The steadier the needle is probably has more to do with how well the gauge is damping things. What gauge are you using? generally TBI pressure is right up the top of a carby type gauge or right down the bottom of an efi type gauge neither of which is great for accuracy.
Find the Manuals up top under Quick links: Manuals. :RTFM:
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by billr »

"EDIT: what car do you have that has a 40 year old pump in it?"

It's a '69 Corvette, I started playing with EFI on it in the early 80's. The pump is from a friend's '76 Caddy, it was getting noisy so I got it for free because he feared it was failing. It is still noisy...
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by turbo conversion »

billr wrote:"EDIT: what car do you have that has a 40 year old pump in it?"

It's a '69 Corvette, I started playing with EFI on it in the early 80's. The pump is from a friend's '76 Caddy, it was getting noisy so I got it for free because he feared it was failing. It is still noisy...
That is as unusual as it is impressive.

David
1976 Datsun 280Z L28ET Garrett GT35R T3-T04E stage3 50 trim 63 A/R housing custom grind cam 2000-6000 rpm 440cc injectors intercooled 18 lbs. boost
3" exhaust turbo back LC-1 o2 sensor Hallman manual boost controller EDIS 6 ignition batch fire 60mm throttle body 5 spd T5 borg warner 3.54 lsd
ironwill11
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by ironwill11 »

billr wrote:Did you ever check what pressure the pump can do "dead-headed"? If that is much over the 13 psi you are looking for, say 20 psi or better, then any poor regulation has to be an FPR problem. Yes, you may need to check that "dead-heading" after the pump has been running for a while, and maybe even check FP with fuel flowing (but not past the FPR). However, I don't think that few tenths of a psi is your root problem. My experimenting has shown that injector flow is rather insensitive to FP, it is far from a linear change. There is an FP vs. flow conversion formula in a recent thread, take a peek at that.

I have not had the time to pull it off of there (doing that requires lots of extra cardboard to prevent spills as I am working in my father in laws garage and I already have a trans oil stain to figure out how to get out). Plan on doing that soon though. Right now I have my fuel pressure gauge T-linked in right before the throttle body and right after the fuel filter I put in. It is fuel pressure sensor that runs a wire back to the digital gauge.

This is the gauge I have (the idea behind the 0-100 psi was that if I ever switched away from TBI into something that requires more pressure):
https://www.maxtow.com/black-green-maxt ... swod68QCvQ

Looking through the flow conversion formula thread now.
ironwill11
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by ironwill11 »

turbo conversion wrote:Me personally, I would replace a 15 year old pump and go from there.

Also if I remember correctly there is a filter in the GM throttle body, it may be dirty.

David
This is/was my inclination as well. I am just getting tire of having to order parts and sit around waiting for them to ship for a week. NJ does not seem to have much of a market for this stuff. I had to walk out of a pep boys when I was looking a rim and told him the exact dimensions that I wanted because it is for a modified vehicle and reiterated, "What year, make, and model?"
ironwill11
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by ironwill11 »

turbo conversion wrote:
billr wrote:"EDIT: what car do you have that has a 40 year old pump in it?"

It's a '69 Corvette, I started playing with EFI on it in the early 80's. The pump is from a friend's '76 Caddy, it was getting noisy so I got it for free because he feared it was failing. It is still noisy...
That is as unusual as it is impressive.

David

Agreed!
I did recently read that late 70s and early 80s used the same fuel pump for their efi.
Will
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by ironwill11 »

slow_hemi6 wrote:It really is hard to get a steady needle indication on a fuel line that has the injectors hammering away at it. Touch the lines and what do you feel. The steadier the needle is probably has more to do with how well the gauge is damping things. What gauge are you using? generally TBI pressure is right up the top of a carby type gauge or right down the bottom of an efi type gauge neither of which is great for accuracy.
This is the gauge I am using:
https://www.maxtow.com/black-green-maxt ... swodWdAO6A

I guess the bouncing up and down is not what concerns me so much but the overall decrease in pressure from 14 - 11 psi like I got last night from start up to fully warm.

Will
ironwill11
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Re: Fuel Pumps, Fuel Pressure, and Frustration

Post by ironwill11 »

turbo conversion wrote:Me personally, I would replace a 15 year old pump and go from there.

Also if I remember correctly there is a filter in the GM throttle body, it may be dirty.

David
I am not sure where this is. I know there is a little filter on each of the injectors which I replaced.

Also wondering about this because when I get it tuned to 13.5 afr idling in neutral then move it into gear and get that tuned to 13.5 afr (which shakes the truck some), then go back to neutral my afr is back up around 14-14.3 (really frustrating- my psi is around 11 at this point). I also noticed that at the VE table I have some big jumps in order to accomplish this. The when in neutral the VE cell is around 36, when put into gear, those cells are around 51.

This is my current tune:
2017-05-06_10.56.29_Frustration.msq
This is a datalog that I took after moving it from gear back to neutral and my afr when up around 14 while my fuel pressure was at 11psi:
2017-05-05_21.04.24_frustration.msl
Will
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