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  1. #1

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    I'll bet you've never seen THIS before...

    Seasoned GH members will know that my skis frequently blow up and exhibit very strange failures. A frequent reply from the techs I work with is "I've never seen that before..." implying that I did something wrong.

    Attached is a clip of the starting issue that my STX-15F race ski has that I have spent about two years trying to diagnose:



    I have addressed and replaced the usual suspect components:
    -new factory starter
    -new battery cables
    -new ECU flashed with the proper 100 octane tune
    -new relay
    -lightly used factory coils, spark plug leads, caps
    -new battery

    What direction should I go now?


  2. #2
    Click avatar for tech links/info K447's Avatar
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    What specifically are the known symptoms of the problem?

    Have you monitored voltages at various points in the starter motor circuit while you are attempting to start the engine?
    Not just voltage across the battery posts (although that is the logical starting point).

    Monitor the voltage between battery positive post and starter motor post.
    Should show full battery voltage, then when Start is pressed voltage should drop to near zero and stay there until Start button is released. If it does not stay near zero start circuit is releasing the start solenoid pre-maturely.

    Voltage between starter motor case and battery negative post would be one non-obvious measurement.
    Should be zero volts all the time. If it rises above a tiny fraction of a volt, there is bad ground connection somewhere.

  3. #3

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    I did measure voltage while cranking in the starter motor circuit and I was losing about 3 volts if memory serves. This is why I replaced the cables. Your point is well taken-maybe because of the high compression of this platform even the smallest voltage loss causes the starter to stall. I will check into this (even though electrical system analysis is not my strong suit).

  4. #4
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    I'd have to give the side eye to the injectors or fuel pump

    measure the fuel pressure at priming at at cranking/running and bag the injectors to get a preliminary look at the flow patterns

    I'd reset the throttle body(tps) if you have the right equipment for that

    let me add, that modded engines sometimes will not start for a couple of spins, you kinda short stroked the starting attempts in the vid

    try a by the clock five second cranking attempt before you start looking at fuel delivery issues

    if it spins up, all good.

  5. #5
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by K447 View Post
    What specifically are the known symptoms of the problem?
    Quote Originally Posted by nmpeter View Post
    you kinda short stroked the starting attempts in the vid ...
    That is what I am not clear on. Did he continue holding the Start button down and the engine simply ceased cranking while the Start button was still being pressed?

  6. #6
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    I zoomed in on the video in youtube and noted the green/red buttons used for the start/stop

    it sure looked like his index finger came off the start button when the cranking stopped, at least to me.

  7. #7
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    Quote Originally Posted by K447 View Post
    That is what I am not clear on. Did he continue holding the Start button down and the engine simply ceased cranking while the Start button was still being pressed?
    It looked to me like yes,...the button was still held but the engine did not continue rotating.

  8. #8

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    Quote Originally Posted by K447 View Post
    That is what I am not clear on. Did he continue holding the Start button down and the engine simply ceased cranking while the Start button was still being pressed?
    I'm sorry this wasn't more clear-YES the engine stalls while I hold the green start button down. This is why I have to repetitively release it and press it again to "bump" the engine over. In this video it over-revved when it finally did start because I had a lot of throttle applied. This helps sometimes but not always.

  9. #9
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by pro1200 View Post
    the engine stalls while I hold the green start button down.
    Quote Originally Posted by K447 View Post
    monitor voltages at various points in the starter motor circuit while you are attempting to start the engine

    Monitor the voltage between battery positive post and starter motor post.
    Should show full battery voltage, then when Start is pressed voltage should drop to near zero and stay there until Start button is released. If it does not stay near zero start circuit is releasing the start solenoid pre-maturely.

    Voltage between starter motor case and battery negative post would be one non-obvious measurement.
    Should be zero volts all the time. If it rises above a tiny fraction of a volt, there is bad ground connection somewhere.
    The idea is to determine whether the start system is continuing to be fully engaged right into and through the crankshaft stall event.

    Is the engine forcing the starter motor to stop rotating or is the starter motor ceasing to attempt to rotate the crank?

  10. #10

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    Quote Originally Posted by K447 View Post
    The idea is to determine whether the start system is continuing to be fully engaged right into and through the crankshaft stall event.

    Is the engine forcing the starter motor to stop rotating or is the starter motor ceasing to attempt to rotate the crank?
    Here's what I've observed so far:

    -when measuring the voltage between the starter and battery positive posts with the start switch activated, the voltage goes from about 12.9 to .8 and the starter stalls. The .8 volt measure varies and the one time it did fire it went to near zero. I'm using a cheap meter so the readings bounce a lot.

    Based on this observation, what could cause the start circuit to do this?

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