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1988 trans am fuel pump problem....need help

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Old 11-20-2017, 07:57 PM   #1
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Car: 1988 GTA Trans AM
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1988 trans am fuel pump problem....need help

1988 trans am
305 TPI

I have been having a starting and stalling issue. I can start the car and it will run for 30 seconds or so and then stalls and does not restart for hours. I did a fuel pressure test and got these results:

Once I turn the key on it jumps to 42 psi
When i start the car it goes down to 32 psi
When i hit the gas it jumps up 5 psi.
After 30 seconds or so it wants to stall.
When it does stall it immediately loses all pressure
when i go to prime and restart the car it jumps to 20psi for a second and then back to 0psi and will not start until the next day,

Heres a video, it starts after i start the car.
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Old 11-20-2017, 10:29 PM   #2
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Re: 1988 trans am fuel pump problem....need help

Unless you have wiring issues, time to swap the pump. Inspect wiring before dropping the rear end though, never know.
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Old 11-21-2017, 12:41 AM   #3
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Re: 1988 trans am fuel pump problem....need help

The drop in pressure after the prime makes me think bad check valve.
The engine will start with 20psi but barely. If you lose that then that makes sense it died and wouldnt start again.
Maybe just before you drop the tank, also check psi before the fuel filter, just in case there might be blockage in the lines or fuel rail somewhere. Probably not but it wouldnt hurt.
I dont know if 30 psi is normal for idle. That seems low. My truck runs 45.
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Old 12-06-2017, 07:07 PM   #4
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Car: 1988 GTA Trans AM
Engine: LB9 5.0 305
Transmission: T5
Axle/Gears: 3.45

Re: 1988 trans am fuel pump problem....need help

Update: I found that the fuel pump relay plug was really greasy. I replaced it and the car started right, now the car idles around 250-400 rpms barely staying alive and it sounds like its running on 4 cylinders. It also backfires like crazy, but it starts up right away every time I turn the key. When I prime the car I hear no noise at all and my fuel pressure gauge is reading 0psi when primed and when the car is running. Does anyone have any idea what it could be? is it a very weak fuel pump?
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Old 12-06-2017, 07:55 PM   #5
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Car: 1992 Z28, 1995 silverado
Engine: 5.7 TPI, 5.7 TBI to TPI
Transmission: 700r4, 4l60e
Axle/Gears: G80 3.23, 3.42


Re: 1988 trans am fuel pump problem....need help

You turn the key (prime the fuel pump) and you dont hear the pump, yet when you turn the engine it still starts up, then thats the oil pressure sensor kicking on the fuel pump. The oil pressure sensor also has a fuel pump relay inside in case the main relay fails (the trucks do as well). So the main relay you played around with might be bad, or the wiring to it. And there is no way your car is running on 0 psi, maybe your gauge went bad.
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