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  1. #1

    STX-12f mystery issues

    I'm new to jet skis and to this forum, but here's the story. Last Friday, I bought two 2004 STX-12Fs (we'll call them A and B) that had been out of the water since last summer/fall. Cosmetically, they were rough but the engines looked good and they both started up and idled pretty well. The digital displays are non-functional. We took them to a gas station whereby Ski A was full of fuel and Ski B needed about 6 gallons to fill up. Went straight to the lake. Ski B starts up and immediately runs great at 50+ mph. Ski A starts and idles but, when given gas, just limps along like it's running only on one cylinder (even with throttle fully pressed). After a bit, it gets over the bogging and takes off and runs great, matching Ski B in top speed. Every now and then, when it was slowed to an idle, it would do the bogging down again for a while and then kick into good performance. Next day (Saturday), we decide to run them again. The battery in Ski A (the troubled one) is dead. While swapping a fresh battery into it, I can hear the initiation sounds (EFI setup or something) happening even with the key in the off position. That explains the overnight discharge but it points to a stuck relay (but where?) or an ignition issue. I try to run the ski at the lake but it stays in that bogged down mode and never kicks up. On Sunday morning, I put in new plugs (the old plugs were dry, nicely greyish-brown except #2 had a bit more carbon), noticed that the electrical short still existed, but then couldn't get it to fire up at all. I drained most of the gas and put in new. Sunday evening, I can get it to start and idle for a while but it never emerges from bogged down mode. By Sunday night and Monday, the electrical short has gone away but still seems stuck in bogged down mode. Any thoughts? The fact that it was able to demonstrate high performance Friday evening suggests it's something more episodic rather than chronic (like blown head gasket). I've checked through the various threads but can't isolate the problem(s). Any advice would be greatly appreciated. - thanks, Chuck


  2. #2

    Update

    Update - when hooking up the battery, I no longer hear the system initialization whirring, but there's still an open circuit even with the key in the off position. It refuses to fire up at all now, and I was able to confirm that none of the plugs are not sparking. What are the usual suspects in a non-sparking situation? Ignition, ECU, something else? Thanks.

  3. #3
    Firestomper247's Avatar
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    http://www.greenhulk.net/forums/showthread.php?t=186939

    Have you read through this? It helped me a lot.

  4. #4
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    I would start by removing the start switch and inspecting it for proper function. Have the skis ever been rolled? Is there any moisture in the clusters? These skis do strange things when the gauge is shorted out.

    Sean

  5. #5
    The dash display does not work and there appears to be moisture within it. Is it drainable? Not sure if the ski was ever flipped, but it probably was. Is there a way to easily bypass the dash display? Also, is the orange on/off switch supposed to be a total battery cutoff? If so, that's a problem as well since it still showing voltage when in the off position. Thanks.

  6. #6
    Update - The ski turns over but has no spark. Also, the battery will drain overnight due to a short even if the orange key is turned to the off position. I took the ski to a shop that had a compatible (2003) STX-12f. The mechanic said he could pinpoint the electrical problem in about an hour. After spending about 3 hours working on it, he could not figure it out but suspected that it was a corroded/shorted connector. He said he one-by-one swapped out the major electrical components (display, ECU, etc.) and it neither enabled it to start OR addressed the short. He thinks it is a corroded/shorted connector, possibly one of the connectors that has pre-key power and post-key power in the same connector. He was a bit frustrated by it and did not want to get into a major harness replacement. He only charged me for the agreed upon one hour but it was of value in that it hopefully has ruled out an expensive component. So, here's my question. Does anyone have any recommendations for a specific connector or harness area that could be the source of the short? If so, which connector and how big of a deal is it to access? Thanks.

  7. #7
    Pain is fear leaving your body.... rlovebk's Avatar
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    Go thru Seans list on the link posted. Check compression and then go thru his list paying attention to the fuel pressure/injectors. If no issue there swap MFD's (display) with the other ski and check.
    Unplug all connectors and check and use dielectric grease on them.
    If none of this works swap harnesses.
    I think it could possibly be the MFD. Once shot they are shot.
    Last edited by rlovebk; 07-23-2015 at 02:35 PM.

  8. #8
    Pain is fear leaving your body.... rlovebk's Avatar
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    The harness swap is not super difficult. Just tight space.

  9. #9
    Quote Originally Posted by rlovebk View Post
    The harness swap is not super difficult. Just tight space.
    Off hand, how much non-electrical stuff would I have to remove to get access (airbox, etc.)?

  10. #10

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    The display is shot. Also, as stated above do a complete compression then leakdown test just to rule out any mechanical engine issues. After that, follow that thread posted above to it's entirety. Tons of good information in there.

    A few points of interest: The connector I had the most trouble with on mine is the Manifold pressure sensor. That one I clean once a year because if I don't I get error messages. Also, clean the fuel injectors, It's not super hard. I made my own with a 60cc Syringe and some alligator clips to actuate the mini solenoids inside. Also check the fuel pressure.

    After all this is done, then start worrying about doing one on one component replacement.

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