Truck is running terribly when warmed up

JAMES CHRISTENSEN

MEMBER
1995 CHEVROLET TRUCK
5.7L
V8
4WD
AUTOMATIC
16,700 MILES

Start the truck up starts fine teeny bit rough. When car or truck warms up it does not want to run no power bucks, snorts, pops up through the throttle body has no power at all. Disconnected MAP sensor did the same thing. Connected it did the same thing. Need to know what the problem is. I've done all kinds of stuff; change spark plugs, cap, rotor and it's still doing it. Only when it warms up. As for running right after I start it it runs okay but not great. Seems like when the truck warms up it does not want to run but when cold it runs okay not great just okay.

1 Reply

CARADIODOC

MECHANIC
33,743 POSTS

Unplug the small plug on the side / back of the generator while the symptoms are occurring. If the engine runs better, suspect the generator has a failed diode. If a load-test verifies that when the maximum output current is one third of what it should be, replace the generator and the battery. With '87 and newer GM vehicles, the redesigned generators develop huge voltage spikes that can damage the internal diodes and voltage regulator, and interfere with computer sensor signals. The battery is the key component in damping and absorbing those spikes, but as they age and the lead flakes off the plates, they lose their ability to do that. The high number of repeat generator failures can be reduced by replacing the battery at the same time, unless it is less than about two years old. The old battery will work okay in an '86 or older model.