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  1. #1
    SplishSplash's Avatar
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    Loss of RPM 8000 to 7600

    Ski: 04 RXP with X-charger, 42 injectors, stock intercooler, Riva air intake, and Solas prop

    Situation: no configureation change.
    Went on a 15 mile cruise, in varing water conditons from glass to 2 foot chop.Some WOT and some not. At start of cruise, was turning 8000 rpm, water tem in the 70's
    On the way back, rpms started to drop, first to 7850 then slowly lower till eventually all it would turn is 7600 rpm. No alarms, Boost pressure looks good (I have a digital gauge that senses MAP sensor levels, actually has worked good over the years as MAP output is drirectly related to boost).

    I figured maybe it was just heat soaked so did not think much of it, but next day, only could get 7850 rpm, got there fast and air was cool.

    Odd thing, when I start it up, runs really smooth for about 4 seconds then it seems to get rougher. OK but not as smooth as when it starts.

    So diagnosis: Spark plugs "look good", no damage or metal or oil on them.
    SC is not slipping but may pull it anyway to check indepth, it already has a washer on the clutch and only at most 5 hrs on it
    Oil is between the marks and clean.
    Pump is clear as far as I can see, and no prop damage.
    Doubt it a boost leak as I am using T Clamps and the hoses are on good, not moved since i put ont the T's, prior to that, it did leep poping off the darn hose.

    So do you guys thinks, New Plugs?, SC Slipping?


  2. #2
    83.0 @ 8400 jhill19's Avatar
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    How many hrs on the ski?

  3. #3
    83.0 @ 8400 jhill19's Avatar
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    I'd try a brand me fresh set of plugs first thing. Do you have a knock sensor harness installed?

  4. #4
    Boost addict hotbird's Avatar
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    Quote Originally Posted by jhill19 View Post
    I'd try a brand me fresh set of plugs first thing. Do you have a knock sensor harness installed?
    +1

  5. #5
    SplishSplash's Avatar
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    About 75hrs on machine. Think i changed the plugs at 50.

    Go with stock plugs or get the Iridums?

  6. #6
    Boost addict hotbird's Avatar
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    Stock NGK is what I have been told to stay with.

  7. #7
    Kaybat's Avatar
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    check your wear ring after plugs...

  8. #8
    monaroman76's Avatar
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    Possibly an exhaust leak?

  9. #9
    Moderator Snoman's Avatar
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    When was the last time yo had your slip checked???Are they ceramic clutch washers or metal???? The thing that makes me think its NOT the SCer is you stated it runs rough at startup...i would check the plugs and also consider checking your fuel pressure...you could have a fuel pump going bad and its leaning out at WOT.....

  10. #10
    83.0 @ 8400 jhill19's Avatar
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    +1 with snoman. What's your compression?

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