After changing my fuel pump, I started experiencing extended cranking only when the motor is warm

DUB305

MEMBER
2002 CHEVROLET SUBURBAN
5.3L
V8
2WD
AUTOMATIC
260,000 MILES

In the early mornings it turns on the first crank and drives with no problem. No misfires, no sputtering, or any idling issues.

So far, I have changed spark plugs, coils, fuel pressure regulator, coolant temperature sensor, fuel pump relay and I am still experiencing extended cranking when engine is warm.

Notice this problem started occurring the next day prior to changing the fuel pump.

So, I decided to leave it off for about 2 minutes and check the fuel pressure valve and when I did there was hardly any air and a little mist of fuel vapors that shot out.

Then I turn the key to the on position and still I get no fuel pressure or fuel until I attempt to crank the vehicle a couple of times.

Also, I tried starting it by taping the gas pedal and that doesn't seem to work so I have to leave the throttle body close and keep cranking it until it builds fuel pressure then it turns on and drives with no problems.

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

Just to be clear, when you turn the key to the on position without cranking the engine you have no fuel pressure.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

If that is the case, we need to find out why the pump is not coming on when the key is turned on.

We start with checking the voltage going to the pump and make sure there is voltage there or there is not.

This could be just a pump issue that it is not building pressure until you crank the engine, but the more likely cause is that there is no power until you crank the engine.

So, let's confirm this.

https://www.2carpros.com/articles/how-to-check-wiring

When the key is in the on position, you should have 12 volts.

I attached the wiring diagram below. You can check this at the relay to start rather than trying to access the pump. If you don't have it coming out of the relay, then you don't have it at the pump.

If you don't have voltage there, then this sounds like a control issue that the PCM is not powering the relay to close the relay.

Let's start with this and go from there.

Thanks

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