Long crank and low fuel pressure

[senrab]

92 GP LE with 130k 3.1L
It has a new fuel pump, relay and regulator. When you turn the key on for prime it barely registers on my pressure gauge. Turn the key on 2 or 3 times and it still doesn't have much. If you start cranking the pressure will jump right up to 45 psi and then it starts. The problem is you have to crank on it for 10 ~ 15 seconds before it builds up to pressure. Once its running it is fine and has no performance problems. It will not hold pressure in the fuel rail when you shut it off.

What have I overlooked or not checked?

Thanks for the help!

[olopezm]

Hi,

Have you inspected/replaced the fuel filter? I'm thinking maybe the filter is too clogged until the pressure builds up enough to brake trough the blockage inside...

Oscar.

[richtazz]

cheap aftermarket fuel pumps are famous for bad pressure valves. There is a one-way valve built into the fuel pump that prevents fuel from back feeding through it to the tank. This is what your problem sounds like. You may want to test your vacuum supply to the pressure regulator as well, just to eliminate it as a possible cause.

[tblake]

Might want to pull the fuel pump wiring diagram.... Maybe Oscar can help. On these cars, if the fuel pump fuse blows, or the relay goes bad, there will be no voltage to the pump during key on. Then when the motor is cranked, the fuel pump can sometimes be supplied voltage when oil pressure builds. Thus starting. Someone with a 94 or older GP want to test this theory? Pull the fuel pump fues or relay, see what happens when you try to start. The car will not fire right away, but then once oil pressure builds, voltage is supplied to the pump through an alternative circuit and the car starts after a longer crank time. Hope this makes sense.

[olopezm]

Here's the diagram, I guess this is a bad day for my electrical skills as I can't find a good way to understand the diagram, looks like today's work caused me a brain freeze LOL.