Fuel pressure GT-RA w/ 5.0

[David Eastman]

I have three questions about fuel pressure on my car. I think I am having pressure problems. I need to know what the pressure is suppose to be at the fuel rail and on the dash at idle. What is the max psi the pump puts out. Is the pressure suppose to bleed off after the power switch is turned off. On all the production cars I have worked on the pressure always stayed at the same psi when switched off.

Thanks in Advance

David

[jmimac351]

David, I pulled this from the corral.net website and it seems to match what I recall from my '92 mustang when I had the stock EFI on it. It doesn't entirely answer your question but it may help. Also, I believe I had an aeromotive pump that did what you describe - bleed pressure when off. I wondered about that as well and was told it was because there was no "check valve" in the pump - it was designed that way. Not sure what pumps come in these cars but it may be working just as it is supposed to from that respect.

BTW, I also recall that fooling with the fuel pressure on the 5.0 is just masking something else as the computer will start making changes to get it where it wants it according to the O2 sensors...

-Jim

+++++++++++++++++++++++++++++++

Fuel pressure should be 38-39 psig measured at a (fully) warm idle with the vacuum line to the regulator temporarily disconnected and plugged (your thumb will work). Hook the line back up, and with a stock set up it should drop into the 32-33 psig range. If you're modded in a way that vacuum level at idle is impacted (cam choices often result in less vacuum at idle), then you won't see as big a drop when you hook the line back up to the regulator.

[David Eastman]

Jim,
Thanks for your reply. I have been doing some more researce and testing. I have two other 5.0 cars in my stable and they both have the same psi at idle. I guess my main concern was the pressure drop after the pump was turned off. I was looking at pumps on e-bay and noticed the new pump has an external check valve on the exit side of the pump. This valve is removeable. My pump doesn't have this valve. So that answers the question why the pressure bleeds to 0 after a few seconds. After doing some research I discovered another test to test the amount of perssure the pump can generate. With the car running at idle and gauge on the fuel rail shut off the return fuel line so the pump dead heads. The pump should make two times factory specs. If the factory psi it 30 you should see 60 with the return line shut off. I saw 100 psi on my fuel gauge meaning the pump is doing is't job.

David