Fuel Pressure Only Increases up to 58 psi, then flatline under boost.

[jspaeth]

Like the title says, my fuel pressure (which I observe via a digital FP gauge in the cabin) increases under boost up to 58 psi or so (about 14.5 psi of boost....since my baseline FP is 43.5 psi), but then flatlines at 58 psi.

Consequently, this means I am having to use more injector than I should for all manifold pressures above 14.5 psi of boost.


This weekend, I rewired the fuel pump directly to the battery.....this WAS successful in some sense.........after doing this, my fuel pressure went up about 4 psi (i.e. it was 47.5 psi when the manifold pressure was 0 psi boost, rather than 43.5, as previously).

Naturally, I thought that I had "solved the problem" (perhaps the voltage to the pump was limiting it's output before)....

SO I dialed the FP regulator back down to the appropriate point (43.5 psi at 0 psi of boost).


Went out for a drive, and STILL, the fuel pressure won't go above 58 psi....it doesn't DROP off, it just stays there, even when the manifold pressure increases.


Any ideas? PS this is a brand new walbro 255 lph HP pump (did the same thing before with my old walbro 255 HP pump).

1) FPR no good? Reasonably new (2 year old) Aeromotive FPR....reliable brand, should be able to easily regulate FP on this setup

2) Stock lines (hard lines to and from the fuel tank) are too restrictive?

3) Something else (I have recently replace the fuel filter, so I don't think that's the problem).


Please chime in ONLY if you have a legitimate idea why this may be happening.


CLIFFS NOTES:

Fuel Pressure increase 1:1 with boost, but won't go above 58 psi (at 14.5 psi of boost), where it flatlines at 58 psi even as boost increases.

Aeromotive FPR (reasonably new), new Z32 fuel filter, stock fuel lines/rail, 740 cc injectors, base fuel pressure is 43.5, NEW walbro 255 lph HP pump (same thing happened with old Walbro pump, too).

[holemilk00]

Which aeromotive FPR are you using?

[jspaeth]

Originally Posted by holemilk00

Which aeromotive FPR are you using?

This one....the A1000:

Aeromotive | 13109 - A1000-6 Injected Bypass Regulator

I BELIEVE it should be good for my application....I am like 99% sure I did the appropriate research 2 years ago when I bought it.....

[holemilk00]

Have you checked and double checked all vacuum lines and fittings?

[jspaeth]

Originally Posted by holemilk00

Have you checked and double checked all vacuum lines and fittings?

No, but I am not sure that a vacuum line being slightly loose would result in the fuel pressure stopping at EXACTLY 58 psi time after time after time for a year straight....

I think if a vacuum line were slightly loose, there would be some slight variations in where it stops....

Furthermore, if the vac line got "loose" or lost it's seal, then I would see the FP drop back down to 43.5 or so....it holds steady at 58 PSI even as the boost continues to increase.

Thanks for the suggestion.

[KiLLeR2001]

Not sure I can be of much help, but if that were my situation I would assume it to be the FPR since its stopping right at 58psi every time. More than likely the internal mechanism inside the FPR is worn out and can't hold anymore than 58psi. I know its not a good idea to start throwing parts at the car but that would be my best guess based on the information given. Good luck.

[cotbu]

Verify that you in fact can turn it up past 58psi, by adjusting the base fuel pressure to 60psi. then set it back to 43.5psi. add pressure to vacuum port on the fpr from an air compressor, turn on fuel pump and gauge, add 16psi or 20psi, log the gauge, verify, done!

Done means if the test failed, you know where to look for the problem.

[Def]

Originally Posted by cotbu

Verify that you in fact can turn it up past 58psi, by adjusting the base fuel pressure to 60psi. then set it back to 43.5psi. add pressure to vacuum port on the fpr from an air compressor, turn on fuel pump and gauge, add 16psi or 20psi, log the gauge, verify, done!

Done means if the test failed, you know where to look for the problem.

This. Eliminate the FPR as the culprit (or prove it is).

[jspaeth]

Hmmmm.

I understand what you guys are suggesting, but if I preload the spring by manually adjusting it to give, say, 65 psi, this MIGHT NOT be the same as it being preloaded to give 43.5 psi and then needing boost in the vacuum port to get to 65 psi.

Does that make sense?

I need to take a look at a diagram of the internals to see if I am making sense here....

Basically, asking it to go from 43.5 psi under no boost to 65 psi due to boost in the vacuum port may not be the same as asking it to do 65 psi without any boost in the vacuum port.

[cotbu]

This. Eliminate the FPR as the culprit (or prove it is).

If it fails? It may be the vacuum source, It could also be the diaphragm in the fpr. I don't want to say buy a new unit. My Aeromotive can be taken apart. I've never clean it, but next fuel filter change i will. So if your unit cant be cleaned and you have swapped reference lines probably the FPR.

Hmmmm.

I understand what you guys are suggesting, but if I preload the spring by manually adjusting it to give, say, 65 psi, this MIGHT NOT be the same as it being preloaded to give 43.5 psi and then needing boost in the vacuum port to get to 65 psi.

Does that make sense?

I need to take a look at a diagram of the internals to see if I am making sense here....

Basically, asking it to go from 43.5 psi under no boost to 65 psi due to boost in the vacuum port may not be the same as asking it to do 65 psi without any boost in the vacuum port.

Yeah pretty much, that's why there two test involved.

[jspaeth]

Originally Posted by cotbu

Yeah pretty much, that's why there two test involved.

Oops, didn't read your post carefully enough....thanks!

[jspaeth]

UPDATE:


Had someone clamp down on the return line while I primed the pump......fuel pressure gauge read about 70 psi or so for about 2 seconds.


This tells me:

1) The fuel pressure gauge DOES work
2) The fuel pump is capable of still producing a fuel pressure of 70 psi or so.


The next test to do is to prime the pump while hooking the vacuum line up to a 20 psi boost source (probably will just used a small air compressor).



This should prove whether or not the FPR is actually working correctly.