I just installed an Electric Fuel Pressure gauge from Auto Meter yesterday. The fuel pressure seems a little low from everything I've read.

Key on = about 42 psi
Engine running at idle = about 35 psi
Engine running with throttle = about 40 psi

It's a 91 Z28 w/ 350 TPI

 

Nothing weird there.

BTW, you 'check' your fuel pressure with the engine running but with the vacuum line disconnected from the AFPR. Thats the most consistent and relevent number to find. Stock will be somewhere between 40-45.

 

Oh, I didn't know that... does that mean I should set an AFPR with the vacuum line disconnected too? I'm still running the factory regulator, but I have a new adjustable reg. from Holley that I want to install. So, the fuel pressure gauge is never going to be real accurate while driving then?

 

PSI you have given look Ok. One question why didn't you install the AFPR at the same time?? I have Autometer gage mounted under my STB.

 

Yes, the vacuum line must be off when setting pressure.

The gauge will be fluctuating as you are driving, except during steady cruising. The main thing you wanna look for is at WOT your fuel pressure should be the same as what you set it at with the vacuum line off. If it's not you have a fuel delivery problem elsewhere.

 

Right, the guage is 'accurate' all the time. The exact values it will be at during driving is all going to be relative to how you have the AFPR set and your manifold pressure. As stated, the best reason for having a guage in the car is so you can make sure you aren't dropping pressure at WOT. Static/idle fuel pressure is one thing, but actually moving quantities of fuel while keeping pressure is another...

 

Ahh, ok that all makes sense. I took that vacuum line off and it read about 45 psi.
I didn't really have time. I want to do that this weekend though now that I have my gauges working properly.

 

I just got a manuel guage which screws onto the schrader valve. My pressure reads 44lbs at idle, constant throttle with spikes to 50lbs off-idle (accel) and engine off at start up. These readings were taken with the vacuum line still hooked up. Are these pressure readings too high then? I ask before I go and take new readings with the vacuum unhooked.

 

By the way, I have an AFPR which I guess is why my numbers are much higher.