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  1. #1

    2010 stx15f hot start problems

    bought 2 last year about this time, one has 50 hours and the other just made 45 hours. when the first one reached 45 hours over the july 4 weekend i started having hot start problems. motor would turn over but no start. not all the time just sometimes.

    did a little research on the net and discovered that it is not at all uncommon for this model to have hot start issues. i figured that maybe the water temp sensor went bad so i order a new water temp sensor and just kept it in the glove box.

    well this weekend it did it again, hot motor would turn over but not start. i unplugged the old water temp sensor and plugged the new water temp sensor and it started right up. i ended up leaving the sensor dangling in the hull for the rest of the day. the jetski started right up everytime for the rest of the 90 mile ride with out issue.

    the second jetski had never experienced this before until yesterday (both jetskis had the same problem on the same day). same exact situation, hot motor would turn over but not start. ended up using the 14mm open end wrench from the tool bag and removed the water temp sensor from the exhaust manifold. i then used the lid of the fire extinguisher container filled with water and dunked the water temp sensor into it for about 30 seconds. the motor started right up, i left the sensor dangling inside the hull for the rest of the day and never had an issue.

    no codes, no high temp warnings, water coming out of the pisser, water out of the pisser cool enough to keep your hand in, what gives? bad run of sensors?

    anyone have any thoughts on this?

    bandm hx

  2. #2
    Live Fast wave15stx's Avatar
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    May 2007
    new jersey
    had this happen with my 2006 sometimes it would take alittle longer to start but always cranked up

  3. #3
    Quote Originally Posted by bandm hx View Post
    removed the water temp sensor from the exhaust manifold.
    The theory is that ECU makes the F/A too lean for re-starting after the temp sensor gets cooked too much/long after some riding - the temp sensor thinks engine is still (too) hot.

    When you remove the sensor, did any oil/fluid come out of the senosr hole on the pipe? Or did you see any grease in there?

  4. #4
    yes, some oil came out but it didnt seem like there was enough oil to completely fill the cavity. basically no drips, but inner threads had oil on them.

    bandm hx

  5. #5
    When you put the sensor back into the cavity, just fill with any grease which is just acting as a heat conducting media between the pipe and the sensor. To check whether the sensor is good or not, check the resistance at room temp at the two pin connector of the sensor. It should read about 293 kohms (very high then goes down as the temp goes up). But even if with a good working sensor you may continue have that hard starting problem because that's ECU F/A issue when the sensor is reading hot.

  6. #6
    finally found time to test the old water temp sensor per the manual and confirmed it was not reading correctly.

    68 degrees reading 255 spec 293
    122 degrees 69 78.5
    194 degrees 16 18.1
    212 degrees 11 13

    the sensor was telling the ecu that the motor was hotter than it actually was. if you are having the same problems it most likely is your water temp sensor....


    bandm hx

  7. #7
    Good job bandm!
    That makes a perfect sense. Since ECU thinks the engine is hotter, the F/A ratio would much leaner than what it should be and it can't start the engine. That's why plugging in a new temp sensor works so that ECU can adjust to the correct F/A.

  8. #8
    I have the same problem with my 07 Ultra LX.
    Can you tell me the exact part number?
    From this drawing, it is showing thee sensors.

    One is 21176B - pressure
    One is 21176 - Air temp
    One is 21176A - temp - I assume it's this one because it comes out of the exhaust manifold.

  9. #9
    you are correct, the one in the exhaust manifold.

  10. #10
    I ordered the sensor and it has not come in yet but i don't think that is my problem.
    I can't even get the ski started at all now.
    just turns over without firing.
    Pulled out the plugs and they look good. no fouling but they do look like it was burning lean. I replaced the plugs for good measure and it still wont start.

    It's an 07 Ultra LX with 24 hrs. Fired perfectly when I bought it and when I took it out the first time. On my first ride it completely died on me.
    I brought it back home and it started fine. Took it out the second time and it kept dying and was a lot of trouble to restart. Finally got it restarted and got it to the dock and loaded. Now it won't start even when cold. Just turns over but will not fire.
    There is 1.5 gallons of gas in it that could have been old but I filled it up with new gas.

    Cant figure this out...

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