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Fuel pressure, regulator not holding pressure

iCasper

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97 SOHC Explorer II, 2WD
SOHC 97. Fuel pressure regulator is losing vacuum from 10hg to 2.5hg in 7 minutes.
Is that normal ?

What are specs for fuel pressure? My one runs with 33psi only when idle.
 


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CDW6212R

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32-35psi at idle with the FPR vacuum line in place, no vacuum leaks. When you hit the gas(or remove the vacuum line from the fuel pressure regulator), the pressure should rise to 38-40psi or so. So check those two conditions first, 33psi at idle is fine.
 




iCasper

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Thanks for giving that missing info. I was not completely sure about it. Pressure goes down 31/32 psi under load. When I disconnect the FPR hose it rises +8 psi (which it should be).
It’s the fuel pump? Airtex unit, 2 years old. I didn’t know that Airtex is crab
 




CDW6212R

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It sounds like the FPR is raising the pressure as it should. When you say under load, what do you mean?

If you have it in park, and open the throttle WOT, that would drop the vacuum in the intake, and to the FPR. But it happens fast, and you can't hold the throttle open for long. The vacuum at WOT drops immediately but the FPR might not react instantly to change the pressure display of a gauge. So that's not a typical way to accurately gauge the fuel pressure.
 




iCasper

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1) after engine off and about 33 psi, I connected a vacuum gauge to the FPR. After 7 minutes the vacuum dropped from 7 to 2.5hg. I should hold the vacuum longer?

2) I did a test drive with the fuel pressure gauge connected. When I give gas (opening the trotte) pressure drops 1-2 psi. There is no other pressure movements.

You said the pressure should rise (under gas).

What is my problem? The fuel pump or the regulator ?
 




CDW6212R

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That test while driving points to a problem. When you hit the gas, intake vacuum drops, and that feeds the FPR, which tries to raise the pressure. You said it goes up while in park and the vacuum line is removed from the FPR. Those two tests tell me the pump isn't pushing enough volume to keep up while the engine is running faster and under heavy load.

Don't measure vacuum at the FPR, that should be a pass fail device. Now if there were a tiny leak internally that bleeds off some vacuum, that could be an issue. But in general that would be extremely unlikely, super rare, and isn't creating the fuel pressure drop. It's likely the FPR is perfectly fine, they very rarely ever fail.

But the pumps often do, as well as the at pump rubber hoses, sometimes develop a leak or split that lets fuel out. If you aren't sure of the tests done, double check the in park test again. Pull the vacuum line off of the FPR, and if it jumps to near 40psi quickly, it's the pump.

I'd say you need to work on R&Ring the pump, and carefully check the clamps and lines in there too.
 




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