96 Suburban hard starting- Fuel pressure problem?

[ELindy]

I have a 96 Chevy Suburban with a 5.7, 350ci engine with central SFI.
It will not fire right up, it will crank over a few times before it starts but it runs good once it starts. I changed the fuel filter and tested the fuel pressure.
When I turn the key "on" the fuel pressure goes up to 60psi for the 2 seconds the pump is running and then it slowly drops to about 40psi and holds. When I start the engine the pressure holds constant at 53psi with the engine idling. While driving the pressure varies from the 53psi at idle to 62psi under acceleration load to 57psi at cruse speed.

I don't want to start throwing parts at it so if you can help pinpoint the problem I will appreciate it.


Eric

[ELindy]

OK,...I found this from MT-2500 on another post and I have posted my pressures below in red.

I am looking for confirmation if it is the fuel pump or the fuel pressure regulator or ?.

Hard to start cold.
Check cold start fuel pressure...key "on" 61psi then slowly drops to 40psi.
Check engine running fuel pressure.....53psi.
Check engine running on the road fuel pressure..53psi-62psi...57psi at cruise.
Then shut it off and watch for fast leak down...slow drop to 40psi & holds.
Pinch off at rubber part or block off return line and check full pressure..80psi.
A few engine have different fuel pressure specs.
But here is the guide lines for fuel pressure testing.
Most Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.
MT

[ELindy]

I was thinking about my fuel pressure problem last night and the fact that it would pump up to 61psi but then slowly drop to 40psi when the pump shut off, and when I had the return line blocked it went up to 80psi and also dropped to 40psi when the pump was shut off so i decided to pinch the supply and return lines right after I pressurized the system to 61psi to see if I had an injector that was leaking. It held pressure so I figured that it had to be bleeding pressure back through the pump. (which it shouldn't)

So today I changed the fuel pump and strainer and it starts right up.

The 2 big things that I notice with the new pump is that after the initial pressurization and the pump shuts off it holds it's pressure and when I crank the engine the pressure holds at about 62psi and I didn't get that before.

I hope this can help someone else that is having a similar problem.

Eric

JOHN 3:16

[MT-2500]

Originally Posted by ELindy

I was thinking about my fuel pressure problem last night and the fact that it would pump up to 61psi but then slowly drop to 40psi when the pump shut off, and when I had the return line blocked it went up to 80psi and also dropped to 40psi when the pump was shut off so i decided to pinch the supply and return lines right after I pressurized the system to 61psi to see if I had an injector that was leaking. It held pressure so I figured that it had to be bleeding pressure back through the pump. (which it shouldn't)

So today I changed the fuel pump and strainer and it starts right up.

The 2 big things that I notice with the new pump is that after the initial pressurization and the pump shuts off it holds it's pressure and when I crank the engine the pressure holds at about 62psi and I didn't get that before.

I hope this can help someone else that is having a similar problem.

Eric

JOHN 3:16

Thanks for posting and letting us know how it went.
Glad I could help with the fuel pressure reading test.
And it looks like you were a fast learner on the fuel pump and pressure testing and leak off testing.
Glad you got it fixed and good luck.
MT

[flht]

ELindy
What kind of fuel pump did you buy, I have had this problem and get the runaround at the parts store,
Thanks

[Burbie95]

I have to replace my fuel pump on a 95C2500 w/ 7.4L. Is it possible to peplace it with a after market external pump in place of the in tank pump ??
Or would I be screwing up the electronics ????
These GM's seem prone to bad fuel pumps (amongst other problems)

[MT-2500]

Originally Posted by Burbie95

I have to replace my fuel pump on a 95C2500 w/ 7.4L. Is it possible to peplace it with a after market external pump in place of the in tank pump ??
Or would I be screwing up the electronics ????
These GM's seem prone to bad fuel pumps (amongst other problems)

No way
You need 26/32 lbs of fuel pressure.
It would take a special external pump to run tkat much pressure.
And external pumps have a high fail rate.
Keep it OEM.
MT