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Thread: Bad headgasket?

  1. #1
    Avi8tor's Avatar
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    Bad headgasket?

    My ski picked up a high rpm misfire. Right around 8200-8300 rpms it will get a dead intermittant skip. If I back off throttle to 8100 rpms it goes away, hit full throttle and misfire. Feels like a bad coil or plug, but I switched out the coils with known good ones, changed spark plugs and still the same thing.


    Is there anyway a headgasket could cause this ( maybe when boost is high?) I did pull plugs and checked cylinders , no steam and I have open loop fresh water. What are symptoms of blown headgasket or what could cause this misfire? I have great afrs at 11.9 when it occurs. Also noticed it seems to crank over a bit longer than used to fire.

    Any thoughts are appreciated.

    05 rxt engine and electronics, riva 8650 ecu.
    Last edited by Avi8tor; 10-07-2012 at 08:06 PM.


  2. #2
    monaroman76's Avatar
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    It doesn't really sound typical of a HG in my experiences. I never had any misfiring, only losing coolant.
    Maybe it could be dirty or low quality fuel?

  3. #3
    Moderator Snoman's Avatar
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    Quote Originally Posted by monaroman76 View Post
    It doesn't really sound typical of a HG in my experiences. I never had any misfiring, only losing coolant.
    Maybe it could be dirty or low quality fuel?

    +1...when my head gasket let go my ski was running the best it ever ran....Pull your plugs and see if any look glossy black...thats a sign of burning anit freeze...

  4. #4
    Mod less, ride more! troyheb's Avatar
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    Its hard to tell with open loop unless you monitor engine water temp and afr's. When my HG went the last time, my engine water temp was up, and then my afr gauge went crazy.

  5. #5
    iron head's Avatar
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    have a look at #3 piston night be lean

  6. #6
    Eric Ocman's Avatar
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    It wont be your HG most likely bro. When you are open loop Im told a good way to know if its leaking is big AFR spikes WOT.

  7. #7
    Avi8tor's Avatar
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    Thanks everyone for jumping in with ideas.


    All 3 sparkplugs the same and don't appear to have changed since last time I had them out.

    Ocman when you say spikes in afr.. mine was varying from 11.9-12.4 when it was missing. Is that a big spike?

    If not headgasket, what are other things that could cause a high rpm misfire. Ski ran perfect cruising at 8100 rpm, if tried to go wide open from there..... it would run like intermittently dropping a coil. I switched the plugs with some I had and switched coils with my riding buddy. His ski continued to run fine with my coils and mine still had the miss.

  8. #8
    Duke's Avatar
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    He is running 100octane from what I collect on previous posts and varying .5 AFR is not a good sign.

  9. #9
    Avi8tor's Avatar
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    Hey Duke, was running 93 octane pump gas and xcharger today. I was thinking the variation in afrs was from where it was skipping, but honestly dont know.

    My first guess when coils and plugs were changed that perhaps the headgasket was leaking under high boost and water on plug couldve been the cause of misfire? I really dont have enough experience with these engines to diagnose.

  10. #10
    speedskixp's Avatar
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    Leaky IC?

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