I have A 89 iroc 5.7 auto that im having it seems like A fuel problem. When fuel pump primes before start the pressure would go too around 42 psi but when the fuel pump turns off the psi would drop too 0 psi in seconds. Also when the engine is running the fuel psi would be 34psi. I have A rough idle and lack of power. when at normal temps it sounds like gas bubbling in the tank and it wont hold idle and would die. Or it would die on me driving like it ran out of gas. I have replaced the following to diagnose the issue: rebuilt motor (stock), 2 computers, reprogrammed prom, 24# denso injectors, 3 fuel pumps (different brands), 2 FPRs, gas tank, 2 fuel filters, all sensors and relays, checked all fuses, ohm the injectors(all getting 16.3 ohm), clamped the inlet fuel line and it held pressure in the rail but makes no sense because replaced fuel pump 3 times. If anybody could help I would greatley appreciate.

 

Did you replace the pulsator or remove it and install the rubber hose instead?

 

Well the first two pumps I used the rubber line but the second hose split on me so I ended up putting in A pulsator and new pump.

 

My fuel pressure has always bled off quick too. I've never quite figured out where the check valve is in the fuel line. The regulator will hold it in the return circuit but the supply line is a mystery to me. Fuel filter?

 

I had a similar problem in my 89. I chased it forever and it turned out that my pulsator had blown out the side and I hadn't looked at it closely enough to notice. You might take a closer look at it. But seeing as you've also tried just a rubber line, that may not be it. Go ahead and look, can't hurt.

 

It's my understanding that the check valve is in the pump, but some aftermarket pumps don't have them. I have also heard that some corvettes have a check valve in the filter that our cars don't have. Food for thought if your pump doesn't have one.