I just checked my fuel pressure and it was only 38PSI and the book says it should be between 41-47PSI. I changed the fuel filter on Thursday and it has a full tank of gas. After starting the car up it only dropped to 37PSI, when its supposed to drop 3-10PSI. Is this more than likely a bad regulator, or something else? Other than a stumble at idle he car runs like a champ though. Would this possibly be the cause of the stumble.

 

was this with the motor at idle? did you try to see a difference with the motor running and the vac line at the rehulator unpluged?

 

IF YOU SHOW 37-38 PSI AT IDLE YOUR OK , 3-10 PSI WOULD BE UGLY

 

No, I was saying that the PSI should go down from 3-10PSI from the 38PSI that I have, so at idle it should have gone down to anywhere from 35-28PSI. At least thats what my repair manual says. Im just wondering if the low reading im getting is causing my stumble at idle and slow starts some days.

 

oh i believe it should have gone up if your filter was dirty, 37-38 sounds like you still have a good fuel pump if it goes down to the 20's your in trouble and when you add some throttle it should be around 41-47 psi. try researching if you dont believe me, any how good luck!

 

Strat the engine. Pull the vacuum line off the fuel pressure regulator (plug it). The fuel pressure spec with no vacuum is 43.5psi, +/-2.5psi, so anything between 41-46psi is fine.

Then reattach the vacuum line. The fuel pressure should drop in proportion to intake manifold vacuum. 6-8psi drop on a stock cam would be normal... so now it shoud be reading in the range of 35-40psi.

So far, if all your measurements were taken with the vacuum line connected, your fuel pressure sounds fine.... but you need one more step.

Take it out on the road (tape the gauge to the outside of the windshield) and run it up to max load/max RPM.... the pressure should stay withing 2 pounds of the "no vacuum" reading.

 

yeah what fred said , i was about to say that j/k, very well said. good luck !