OK, so I was checking my fuel pressure today due to some stumbling and stalling I've been having at part throttle. First I checked it with the key in the accessory position and it read 46psi(which is fine because I have an AFPR set at 48psi)) Then when I checked it while running, it read 48psi. Which is weird because the manual said it should be lower by 10 lbs or so while running.

What gives? Is it a clogged injector creating extra pressure in the rails? Also, does the high reading suggest that my fuel pump is fine?

I'm stumped.

 

?????
Anybody?

 

Clogged injectors can't raise the fuel pressure to my knowledge, and the manual's thing about pressure dropping by 10psi when the engine is running may not be accurate.

On mine, the regulator is set for 46psi and that's what it holds whether the engine's running or not, as long as the fuel pump is powered.

A decent way to test for a weak fuel pump is to check pressure at high revs. I use a gauge w/ a long hose, thread it onto the Schraeder valve, and duct-tape the gauge head to the windshield where I can see it. Take the car out for a flog and keep an eye on the gauge...if it drops off as the revs increase, your pump is under-delivering.

 

Well, the stumbling is occuring at light throttle. When I go heavy into the throttle or at WOT, the car feels fine. I thought it might be the pump or an injector, but wouldnt it get worse at full throttle if that was the case?

 

With the ignition on, the fuel pump will get about 12.6V. With the engine running, the pump will get around 14.1V. That can explain the difference in pressures between the engine off and running.

Your problem may be that the vacuum chamber above the spring is leaking. The FPR should lower the fuel rail pressure between 4-7 PSIG when vacuum is applied.

The stumbling at idle an part throttle could be clogging injectors, poor spray patterns, or it could be vacuum or compression leaks, ignition problems, or other non-fuel related items. You need to get the FPR working correctly, then perform a power balance test on the injectors.

 

Anyone have a pic or a good description where the Schraeder valve is?