5.7 vortec long crank

[slow_c1500]

Hey guys new member here. I have a 96 c1500 5.7 vortec that is having trouble starting. It always starts every time, but I usually have to crank 5-6 seconds. I should also mention that once it made a grinding sound, but only once out of the hundreds of times that I’ve started it. It doesn’t seem to be a temperature dependent problem. Has new cap, rotor, plugs, wires, mpfi spider. I have also tried cycling the key on and off to prime the fuel pump, but that doesn’t seem to help so I think it’s not a fuel pressure problem. Any help? Thanks in advance.

 

[Schurkey]

What is the fuel pressure during "prime"?

First Guess: None. Engine has to crank long enough to build oil pressure before fuel pump will run. If you're really, really lucky, the fuel pump relay has failed, and it's not a wiring or ECM issue.

 

[slow_c1500]

What is the fuel pressure during "prime"?

First Guess: None. Engine has to crank long enough to build oil pressure before fuel pump will run. If you're really, really lucky, the fuel pump relay has failed, and it's not a wiring or ECM issue.

Could a small oil leak at the oil cooler lines be related to this, since it would be decreasing the oil pressure?

 

[Schurkey]

No.

If the engine has ~7 psi of oil pressure, the switch closes and supplies a power path for the fuel pump.

The basic issue is not oil pressure, it's the failed fuel pump relay, fuel pump relay harness, or failed ECM.

 

[slow_c1500]

No.

If the engine has ~7 psi of oil pressure, the switch closes and supplies a power path for the fuel pump.

The basic issue is not oil pressure, it's the failed fuel pump relay, fuel pump relay harness, or failed ECM.

Ok. I should also mention that the truck usually starts right up in the morning, after it’s been sitting overnight. It’s just during the day when it hasn’t been sitting as long, it cranks for a while and starts. I don’t think it is related to the outdoor temperature, instead how long the truck has been sitting. Is the fuel pump wiring/relay/ecu still the most likely culprit?

 

[Schurkey]

Is the fuel pump wiring/relay/ecu still the most likely culprit?

What is the fuel pressure during "prime"?

 

[slow_c1500]

I don’t have access to a fuel pressure test tool but I will let you know once I get one.

 

[Caman96]

I don’t have access to a fuel pressure test tool but I will let you know once I get one.

Auto parts store, most have free rentals.

 

[slow_c1500]

Ok I got the Maddox fuel pump test gauge. The fuel pressure is 54psi for the first 2 seconds when the key is turned to the on position. Then it clicks, and the pressure slowly drops down.

 

[PlayingWithTBI]

The fuel pressure is 54psi for the first 2 seconds when the key is turned to the on position. Then it clicks, and the pressure slowly drops down.

Yep, you have fueling issue(s).