98 Fuel problem that has everyone stumped. I am helping a board member with his car, here is what we have so far. After a previous pump install he had done issues started to arise.

Previous symptoms after 1st fuel pump install are

The car would not hold pressure and had to be primed prior to starting. this eventualy led too, the car not starting at all. Now the pump kicks on for .5 seconds and shuts off and thats it!

New symptoms

A. Then the car will not start at all.
B. Pump kicks on for .5 seconds and shuts off
C. Gauge on rail would show 60 psi and fall back to 0 (however the fuel rails were still dry)
D. Pump would shut off even when activated via EFI Live


So far I have checked the fallowing

A. Filter and main line clear. (Checked with air)
B. Return lines clear (checked with air)
C. Fuses & Relays good
D. No leaking or broken lines in the pump assembly.

When checking pressure at the fuel filter it would build pressure during the prime cycle and then fall back to 0 as soon as hte pump shut off.

While testing the regulator with a mighty vac it was not holding pressure at all. The fuel just pored straight through the return line back into the tank. The regulator was replaced. This stopped the immediate free flow of fuel back into the tank and allowed pressure to be sustained for a longer period of time, however it would still return to 0-10 psi after about 5 min.


I assumed the pump was bleeding it back into the tank. So I replaced the pump, Now it holds pressure at the filter.

So far Ihave now replaced
A. Fuel Pump
B. Regulator
C. Filter

All new symptoms remain the same except C. Now 0 pressure is read @ the rail during the prime cycle but approx 60 psi @ the filter.

I am starting to think there was a multitude of reasons for all the symptoms yet there are some things that puzzle me.

With the regulator being bad and stuck open and not allowing fuel to reach the rail why wouldn't the pump cycle fuel back into the tank when activated via EFILive even if there was a blockage in the supply line?

Is there any sensor, switch or anything else that tells the pcm to shut the pump off besides the inertia switch?

Could the PCM be shutting off the pump even if being activated by EFI live or a Tech II (such as a fault in the PCM?)


Would a blockage of some sort such *** a internally collapsed or kinked soft line like the one in the engine compartment or something in the fuel rail cause all of the symptoms above and cause the regulator to go bad?


Any and all ideas are welcome at this point. I realy did not want to have to cut the wire harness and hot wire the pump if there is another way.

Thanks guys!

 

anyone know if a chain reaction of parts could stress anything in the PCM to fail?

Such as a FP with a non working check valve, then the regulator sticking open causing the FP to work twice as hard to keep the volume and preasure up?

If not what would cause the PCM to command the fp off and fail?

 

No blockage between filter (60 psi) and rail (0 psi)...?
GM.STATE02 "Vat Fuel Disable" is active or inactive...?
Multimeter should show BAT voltage to fuel pump for 2 seconds at "key to on".

 

No blockage, however the regulator was stuck open. I am sure the fuel was just cycling back to the tank because there was no resistance (open return line) and with the old pump only comming on for <.5 seconds it never had a chance to make it to the rail. A diffrent pump cycled for a full 2 seconds after a few connections were cleaned, the old pump was still only a 1-1.5 seconds. But noticbly shorter cycle.

There was < .3V drop at the pump. (off the top of my head)

A diffrent pump and new regulator reslolved the issue of no fuel to he rail.


What I did find in old codes was a PO601, also when the PCM was put in a known working car it brought up the PO601 again.