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97 GMC C1500 Misfire

This topic contains 3 replies, has 2 voices, and was last updated by Tom Tom 7 months, 1 week ago.

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    Topic
  • #953813
    Tom
    Tom
    Participant

    Hi all! Sorry for the wordy post. Short version is I have a #2 misfire and everything appears to be working properly, but suspect the thing is just worn out and needs rebuilding/replacing.

    1997 GMC Sierra C1500
    5.0 with 188k

    Quick history:
    Bought the truck needing intake manifold gaskets. While I was in there, it also got a MPFI upgrade and distributor as they were both trash. The motor was pretty sludgy under the valve covers and in the valley. Cleaned that up as best I could.

    The good:

    – Timing was set correctly with a scanner.
    – Vacuum gauge shows on the low side of good, and steady throughout RPM ranges.
    – Fuel pressure good and holding.
    – I’m assuming the injectors are operating correctly, since they’re under the intake and I can’t test them individually. I did remove the upper intake again to make sure I installed the spider correctly and didn’t see anything out of place.

    The bad:
    – I have both P0300 and P0302 codes. DashCommand only shows misfire counts on 2.
    – Compression on all cylinders is between 140-150 dry. Adding oil to #2 raised compression to 170, which seemed significant.
    – All plugs show some oil fouling but I don’t run the truck much, and have tried new plugs with no improvement.
    – Spark seems strong at the #2 plug (it shocked me) but pulling the plug wire while running shows no significant drop in idle, especially compared to other cylinders.
    – Fuel trims are all over the place

    Does that about cover it? Worn rings and/or heads? Can a mechanic do any additional scanning or diagnostics? Truck is in average condition for its age and I’m not sure it’s worth a crate motor, if it ultimately needs a new one.

    Thanks for reading. Your thoughts are appreciated.

    Tom

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  • #953814
    Nightflyr *
    Richard Kirshy
    Participant

    You state vacuum om the low side of good and fuel trims all over the place.
    Might suggest smoking the engine and look for any vacuum leak(s)

    #953815
    Tom
    Tom
    Participant

    You’re probably right there. I haven’t smoked it but using propane I’ve found and fixed a couple vac leaks. And now that I’ve got plenty of time I’ll build a smoker and report back. Thanks!

    #954318
    Tom
    Tom
    Participant

    Well, fixed it, it was all my fault. Turns out I bent a pin on the fuel injector plug. Straightened the pin and carefully plugged it back in. No codes and runs great 😀

Viewing 3 replies - 1 through 3 (of 3 total)

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