Big Problem With 2002 Gmc Sierra

2002gmc1500 · October 4, 2009

I am having a problem with my wife's 2002 GMC 1500 Sierra Pickup, with the 5.3L V8 and automatic transmission.

The problem started with the truck on the highway. With the cruise control set, she said the truck suddenly downshifted going up a hill, made a strange noise, and now the CEL is on. I drove out to her location (about 1 hour away) and the truck is missing pretty badly. According to the scan tool at the local parts store, its getting the code "random cylinder missfire".

I already had a new set of plugs for the truck and had brought them along, but changing them did not help. I also tried removing the coil pack plugs one at a time and listening at idle and while reving for a miss, and could not track down a local problem on a specific cylinder (each time I pulled one off, it made a distinct difference to the idle/rev).

The truck still had enough power to cruise around 60~ MPH, but no more, so I headed home with it with her following me. About 20 min in, going up a large hill the truck really started to struggle and miss. Even after we got over the hill and started on the flat, it would not accelerate. She reported at this point the truck was smelling pretty bad. I managed to creep to a offramp, where it died and would not restart. I finally got a restart, and pulled it onto a gas station parking lot that was luckly really close, but it will barely move at this point, with an extreme miss and absolutly no power (nothing over 10 MPH at max).

Not sure what is going on here, strange that that problem got worse over time IMO. All fluid levels look ok, I don't see any vaccum lines off etc, and it is now missing on ALOT more than 1-2 cylinders, must be missing on virtually all of them to be running so poorly at idle. HELP!