05 hummer h2 misfire

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  • #991232
    Chris sChris saumur

      So this one has me stumped. I am working on a 2005 hummer h2 and it came in for a SES light and a couple other things. Let me start by saying the vehicle has headers, no cats and an aftermarket intake. Well I scanned it and it shows random misfire and b1s1 o2 heater circuit.

      The misfires are only on #5 and #8. So I swapped coils, plugs, wires and injectors from the cylinders next to them and it is still there. It only misfires above 1500 rpm. I pulled the valve cover and inspected the push rods and valve springs and there was no issue. I sprayed around the intake manifold with brake clean and watched fuel trims with no change in them so I know that isn’t leaking.

      Then I tried to do the crank cam correlation learn and found that there is no fuel cutoff. It revved very quickly up to 6k and I let off. So I plugged in the scan tool again and checked the software version for the pcm/ecm and it said unknown calibration. I tried reprogramming it with the current calibration and the it stated that it failed with a message containing the bytes of the program that it failed to program on. Oddly the calibration now says current but I still have no fuel cutoff so I can’t do the cam and crank correlation learn. I think this computer might have a tune or something but I don’t have that kind of experience.

      I forgot to mention I also did a leak down test and it passed with flying colors.
      So I’m not really sure where to go from here. My instinct is to recommend to replace the pcm/ecm. I just got moved from apprentice to technician 3 weeks ago and this one seems to have gotten the better of me.
      Do you guys have any input or ideas?

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    • #991233
      Chris sChris saumur

        I should also add that watching the live data misfire monitor, cylinders 5 and 8 misfire faster that you can even count out loud. It’s pretty bad

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