Mechanics

MODELS FUEL PRESSURE - HOW LOW IS *TOO* LOW?

1998 GMC Other

Engine Performance problem
1998 Other GMC Models V8 Two Wheel Drive Automatic 183000 miles

Greetings, I recently started experiencing very poor acceleration at wide open throttle, and/or near wide open throttle, for instance when accelerating on the on-ramp of a highway. Moderate acceleration is fine though and at an idle, the engine is silky smooth. I've already eliminated many possibilities, but I'm presently suspicious of fuel pressure. The specs for this vehicle are supposed to be 55-60psi, and 66 at WOT. I put a guage on it and see that at idle it's about 55, mild to moderate acceleration it's about 58, but it drops to about 52 at WOT. My question is this. Is 52psi at WOT low enough to possibly be causing my problem? I replaced the pump about 2 years ago but never measured the pressure before this. Also, can the ECM control fuel pressure (measured at the test port)? Could the pump be good, yet the ECM is preventing it from supplying the specificied 66psi at WOT? Thanks in advance. --Mike
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Mjwsw
August 3, 2008.



Pump is no good. These engines will not even start when cold on 52 psi. Its a very high pressure and high volume system. Make sure when you replace the pump to use a ac delco pump, it will cost a little more but its worth it. Also check the connector for the pump real real close, look for slightly discolored connector or loose terminals, if any are questionable replace the connector, gm sells the connector because they go bad so often and usually cause intermittent no start due to lack of fuel volume.

Tiny
Mastertechtim
Aug 3, 2008.
Thanks Tim. I suspected as much, but just wasn't sure how low was *too* low.

My only other question is this. Can the PCM be regulating the pressure down (even with a good pump) because of other peripheral issues? Like O2/EGR sensor input issues? Thanks agian.

--mike

Tiny
Mjwsw
Aug 3, 2008.
No, absolutely nothing to do with it. Seperate issues. Pump is the only possible cause for the low pressure.
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Tiny
Mastertechtim
Aug 3, 2008.

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