97 GMC running issues

Brosuf · June 25, 2016

Hello everyone, I have a 1997 GMC K3500 with the 7.4L 454 in it. Now I have tried a lot of stuff over the last 6 months, I am turning to some forum help now. It seems like every time I fixed one thing, there was a different thing wrong that contributes to the issues. All in all here is where I am at. First off the truck is in great condition and only has 97,000 miles on it so I figured it was worth dealing with. The truck doesn't seem to be consistent at this point. If I go out and fire it up first time of the day, the truck runs absolutely fine. No sputtering, no loading up, no idle issues at a stoplight, and no towing issues. Now if I turn it on and drive it down to the store and shut it off, I start it back up and it runs rough, throttle response sucks, sputters like crazy, and I have to feather the fuel to get it to accelerate about 2,000 RPM's. Now at first it used to have codes it would throw, so I changed the sensor or part associated with the code. I have changed the mass air flow, map sensor, injectors, fuel pump, fuel pressure regulator, cap/rotor, plugs, and the upper and lower intake gaskets. At first I thought a lot of it was an internal vacuum leak which is why I went throw and redid the I take gaskets and it was fully warranted. They were terrible and blown out. Now that I switched them out it is still not running normal. Now I am starting to think the PCM may be going bad. There are no codes being thrown, the truck runs so bad after the first fire up. If anyone has any input on this I thank you in advance.

Brosuf · June 25, 2016

I already did a seafoam treatment when I first got it and run it through every oil change. And I did replace the fuel filter as well when I did the pump. I have not checked the EGR valve yet, I will have to check that out

Duelin · June 25, 2016

Have you looked at the EGR valve?

diyer2 · June 25, 2016

I would take an easy cost effective approach myself.

Seafoam in the fuel tank at 2 ounces per gallon, run as much through it as you can before refueling.

Doug_Scott · June 25, 2016

Don't see it mentioned, and it was likely already considered, but, what about the fuel filter? Fuel injected engines behave poorly with a restricted fuel filter. Plugged exhaust also has a similar effect.