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Erratic Ignition (or something like that)

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  • Erratic Ignition (or something like that)

    I mentioned in the thread about last SCS that I did not make it there, thanks to loss of power at full throttle.

    In the meantime I checked and cleaned the injectors (spray pattern looks good visually), replaced the ignition coil and wires and checked the injection pressure.

    Guess what...now the car barely runs at all. One thing I noticed is the timing light is very erratic and the displayed rpm flips back and forth between 2x the actual rpm (normal for the wasted spark system) to 1x actual rpm.

    If my ECU is not broken (aargh!) then I guess it can only be the crank position sensor.

    Any other ideas? I will swap the crank sensor tomorrow and if that does not help then I need to get a scope from work and try to get more into detail.

  • #2
    Coil Pack?

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    • #3
      Originally posted by Doug Liedblad View Post
      Coil Pack?
      Swapped that out already. No change.

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      • #4
        I think it's time for the new SVT engine. Just happen to know where one is.

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        • #5
          Originally posted by Doug Liedblad View Post
          I think it's time for the new SVT engine. Just happen to know where one is.
          Sure...one evening of work and I have the SVT engine running.
          As it happens I also checked compression, just to be sure and found it 200,190,200,190. Has not been that healthy for years. The valve job and unsticking the piston rings last year was probably worth it.

          Now...I hooked up the scope to the coil pack input and saw the pulse train ticking along just fine, no gaps and no double pulses. This hopefully eliminates the ECU or crank position sensor as a reason.

          One thing I did not change yet was the plugs themselves because they look good and the iridium plugs supposedly last forever. So I swapped some age old and well used Bosch Platinum4 plugs in and, the instability with the timing light was gone and the idle was much smoother. I am a bit confused. Maybe that solved it but I have not tested it at speed or under load yet.

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          • #6
            i had one cylinder that was popping back into the throttle bodies a couple of years ago. Drove me nuts, checking everything. I moved the plug to another cylinder and the popping moved too.

            New plugs fixed it and they were fairly new special Nippondenso plugs that were supposed to be the best around.

            Went to cheaper plugs and no more problems.

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            • #7
              Well. went on the freeway tonight and the car ran like new. Actually better. Maybe I should not complain but I still have a hard time to believe it was the plugs. But lacking further symptoms I don't know what else to check.

              I only hope it was not some intermittent wiring issue that will rear its ugly head in two weeks, driving across the Montana back country.

              I will do a more thorough road test Saturday morning and if possible go with Magnus wherever he wants to go Sunday morning.

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              • #8
                If it is not the plug, it could very well be the crank sensor.

                When they go, they usually do so gradually and start to fail when they get hot. Your ECU should have an error code for it.

                /Magnus F.

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