[Turbo Downer]

My 1997 GMC Jimmy will not run without misfires. It all started when I tore it down to do headgaskets because my cylinder 1 was low compression. Got it all back together right and now it won’t run well (p0300 dtc). I just replaced spark plug wires because I had torn the boot on one and figured why not replace all of them. I also ordered a new ignition control module and maybe that’ll help. Anyone have any useful input?

Update: I finally got it running well, the problem all along was three bent injector pins on the big connector. Itran great and no misfire at idle and no overheating until about the four of driving it. I passed someone on a highway and revved it a little higher (not past 4000) and it was fine until I got to a stop sign where I felt it misfire a couple times, didn’t think anything of it but it’s gotten progressively worse and it’s back to the point of where it was before the head gasket job. Makes me think that maybe it already has a freshly blown head.

 

[bk2life]

It all started when I tore it down to do headgaskets....... Anyone have any useful input?

you answered youre own question.
It all started when you tore it down. Go back to square one and redo the job. Probably have the timing off, or a gasket that didn't seal correctly, or broke an injector, it is impossible to diagnose over the internet.

 

[Hoosier Rick]

Did the repairs fix your low compression on #1? Do you have a scan tool to monitor misfire counters? I'm wondering if you have the injectors routed to the right cylinders. The cylinder number is stamped on the injector block.

 

[420blazer03]

There’s any number of things that you could have screwed up along the way if you dont know exactly what you are doing with each and every step along the way. It could be anything from you werent clean enough and crap got into bearings, piston rings, oil capillaries etc to messed up timing, unseated gaskets as stated above, forgot to plug in a sensor.

the point is, you need to go back and check each and every bolt, nut, connector, plug wire, and distributor timing. If you haven’t found the issue you get to choose whether or not to go back and redo it properly or junk it.

Id pull the distributor and check that the gear is on the correct way (there are two ways to put the gear on, and only one way is correct - look it up on here! And look into distributor phasing while you’re at it…).