Diagnostic help - 1988 GMC K2500 5.7L

[DJK555]

RE a 1988 GMC K2500 5.7L. I'm trying to diagnose a fuel mixture issue that only occurs after driving for a while - full warm up - and then stopping for some time and partially cooling. Under those conditions it starts great but hesitates on acceleration often setting a lean exhaust code. Once warmed up to full operating temp it runs great again. Any suggestions?
David

 

[Zembonez]

Re: Diagnostic help

Bump.

 

[PenguinLTZ]

He has mentioned having the incorrect injectors if you recall

 

[Kennyray]

If you are running the 5.0 injectors it might not be getting enough fuel when it's warm. When cold the computer is compensating. My best guess.

 

[DJK555]

Thanks for the bump on this earlier post. As mentioned I am running 5.0L injectors on a 5.7L. While that may cause some driveability issues the actual diagnosis, as determined by a GMC dealer tech, is a faulty fuel pump. I replaced the fuel pump two years ago after a failure. According to the tech, aftermarket fuel pumps for these engines have a tendency to experience dissinigrating impellers which clog up the filter, particularly on vehicles that sit a lot. I replaced the filter with the pump and two years and only 8oooKM later it was partially clogged causing a lean condition. That's the techs story and its looks like it is correct. So now I'm replacing the pump again with a Delco and while see how it runs before deciding if I will replace the injectors.
Hope this help someone else.
David

 

[Draenor]

I don't see how the pump can be faulty if the truck runs great at operating temperature. Not saying that couldn't be the problem, just doesn't add up.

Can you test your fuel pressure?

 

[Zembonez]

I don't think it's the 5.0 injectors. They would cause a problem all the time if that was the problem. I agree with John. Need to check fuel pressure.

 

[Texas Jim]

Is it ever a little bit hard to start when cold?
Has your mileage dropped since this started happening?
What is your fuel pressure ?

Have you checked/replaced the fuel pressure regulator yet??

 

[DJK555]

The tech at the GMC shop check the fuel pressure. The only change made to date is the fuel filter and that seems to have corrected the original problem. I'm exploring the injector issue as it may imporove the trucks camper hauling ability. I will be pulline out the fuel pum in the next week or so to replace with a Delco unit. I'm also changing the sender to get around the corroded flare nuts. I'll report back on what the pump look like.
David