AdsoYo

I've been chasing several issues with my new 383 and decided to focus on the fuel system. I bought a fuel pressure gauge and when I turn on the ignition, the pressure will spike at ~40 psi then drop to 0 within a few seconds.

The car has never been easy to start, I have to crank it for a few seconds. When it finally does start, it'll drop to ~500 rpm then catch itself and maintain a normal idle. During normal driving, the scanmaster will show sporadic knock retard that I haven't been able to find a pattern for, but I suspect it's related to this fuel issue.

When I turn on the ignition with the fpr's vacuum hose connected or disconnected, the pressure will spike at ~40 psi then drop to 0 within a few seconds. When the car idles, the fuel pressure holds steady at 38 psi with the vacuum hose connected. I need to buy a longer hose so I can tape the gauge to my window and drive around, that'll be for tomorrow.

There was no fuel or fuel smell in the fpr's vacuum line. When I turned on the ignition with the fuel injectors out, none of them leaked. This means I can rule out a faulty fpr and faulty injectors right? Since pressure builds initially, I can rule out bad fuel lines and fuel filter right? Would that leave the fuel pump as my problem?

The fuel pump is a walbro 255, fpr is stock, injectors are Ford SVO 30#, fuel filter and lines are stock. All components except for the fuel lines have 7000 miles on them.

ak95ta

What type of FPR, stock? Aftermarket FPR's like the aeromotive unit do not hold fuel pressure when the pump shuts off. If it is the stock FPR, then the check valve in the pump in the tank is bad.

AdsoYo

FPR is stock. I think you're right about the check valve. This sucks, it's a brand new pump.

ak95ta

Well, there is still a chance that the stock fpr has gone bad if it is a new pump in the tank. Too bad you didn't have another one lying around to try out.

AdsoYo

I took the 5 nuts off the fuel tank where the pump mounts so I could easily hear the pump (I cut a door in the trunk). After I turn the key and the pump primes I can hear what sounds like air bubbles as the pressure drops to zero. Is that what a bad check valve sounds like or is there something else going on?

When the car is running, and when I'm driving it, the pressure never falls below 38 psi.

SoloExceptional

I've never heard a bad check valve, but from what I know. That's exactly what it would sound like, because it is supposed to keep the fuel rail pressurized and the fuel from coming back into the tank. I'm gonna go with fuel pump check valve as well, especially if you have 38lb on the rail with the vacuum line connected. What kind reading do you get if you disconnect the FPR vacuum line while the car is idling? It should bring the idle/pressure up pretty good if it's working right.

AdsoYo

When I disconnect the vacuum line the pressure rises to 44 psi.

SoloExceptional

FPR is good, check valve it is