Will not stay running

DUROLAST330

MEMBER
1990 GMC SUBURBAN
5.7L
V8
4WD
AUTOMATIC
150,000 MILES

The truck starts and runs for approximately 5 minutes then shuts off. Sometimes it will start back up but runs rough other times I have to wait a hour or two. Fuel pump and throttle body are fine. Injectors are squirting fuel during start up. I have replaced the ICM. Not sure what is going on?

5 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

Good evening,

First, you need to check the fuel pressure when it does not start. The pressure is critical.

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

You also need to test for spark. When you crank the engine, does the tachometer move up? This is when the engine will not start.

https://www.2carpros.com/articles/how-to-test-an-ignition-system

https://www.2carpros.com/articles/car-cranks-but-wont-start

Roy

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Friday, September 13th, 2019 AT 6:16 PM

DUROLAST330

MEMBER
3 POSTS

Fuel pressure and spark are fine on initial start up. As stated it runs perfectly for approximately 5 minutes. Fuel pump and filter have been replaced. Injectors are clean. Pressure is good and injectors are spraying fuel after the engine shuts off. The only recurring issue I have had is ICM has been replaced twice in the last couple years. Sometimes the truck engine will start back up after it shuts off and sometimes it takes a while before it will start back up. I suspect possible computer issue but not sure how to test it. I will try and get a video of what it does tomorrow.

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Friday, September 13th, 2019 AT 6:37 PM

ASEMASTER6371

MECHANIC
52,797 POSTS

Okay, I still need the fuel pressure spec. Even if you put in a pump does not say it is good. Low voltage to the pump could cause low pressure.

As far as the injectors still working when the engine is off, that tells me the ECM is no good.

Roy

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Monday, September 16th, 2019 AT 3:51 AM

DUROLAST330

MEMBER
3 POSTS

Okay, I will get the fuel pressure reading. I should have clarified the injectors still spray fuel while trying to start the engine after it cuts off. They are not spraying fuel without me cranking the engine over.

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Monday, September 16th, 2019 AT 6:43 AM

ASEMASTER6371