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  1. #1

    Exclamation 2006 STX15F starting problem - voltage drop - weak crank

    Last time I was riding I noticed that the jet ski had trouble starting right before I put it on the trailer (luckly it was the end of the day). So I thought it was a low battery or bad starter. Now I've been trying to fix my 2006 stx15f for a while now and nothing seems to work. Battery voltage measures 12.6v. When I start cranking it, voltage to the engine drops to about 7ish volts and rotates the crank 2-4 times then seizes. I've jumped the ground/negative wire from the battery to the bolt of where the stator is and it cranked very nicely twice in a row so I thought I finally found the problem. Ordered a fresh negative wire, installed it and still, same problem. So I've again, jumped the negative wire from battery to stator and it didn't change a thing.

    Starter - At first I thought it was the starter, so I replaced it with a brand new one, that seemed to fixed the problem. Then I parked them for the off season for a few months. I would periodically start the jet ski to make sure nothing is seized. I live in FL so nothing freezes. They sit outside with a cover. Then after a while it wouldn't start.
    Fuel pump - It wasn't starting because the fuel pump wasn't working, so I replaced it. Fuel pump pumps fuel fine now, no problems there. Also new fuel filter. But still it cranks very weakly.
    Spark plugs - new spark plugs. I noticed when the spark plugs are out, the engine cranks very easily and freely. All 4 plugs do spark when I crank the engine.
    Battery - I've replaced the battery and no luck. I've taken the battery from my other jet ski that works just fine and put it in this one, didn't fix the problem. I know the battery is working fine because it cranks the other jet ski with no problems and is fully charged.
    Solenoid - Took the starter solenoid from the other jet ski and installed it on this one - no change.
    ECU - Took from other jet ski and no change.
    Voltage regulator - Same thing from other jet ski, no change.

    I'm now thinking that there is an open circuit somewhere and I have no idea where and don't know how to find it. So, I'm now thinking of replacing the whole wire harness and hope that fixes the problem but I'm worried that it might be a problem with one of the sensors. Also, my screen is sun faded and isn't working and I don't want to spend $500+ on a new dash.

    Any tips will be greatly appreciated!


  2. #2
    steve45's Avatar
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    Welcome aboard, Oleg!

    I've got an early STX-15F, and I had an STX-12F. Both of them had the ground wire attachments re-worked before I bought them. I never figured out why, but it was obvious that it wasn't original. Perhaps there was a problem with the original ground connection for some reason.

    If it cranks well with the plugs out, I would think it's not getting enough current to the starter.

  3. #3
    How can I test to see if it's the issue with the positive wire without taking off the intake manifold? Can I just jump the positive from the battery to the stator bolt? I'm worried that something might get fried...

  4. #4
    steve45's Avatar
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    I was talking about the ground wire, not the positive wire.

    Are you talking about jumping from the + battery terminal to the starter terminal?

  5. #5

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    Oleg- You are describing the EXACT symptoms that my STX-15F race ski has. I have been fighting a starting issue for over two years now. My symptom is the starter stalls but I can sometimes get the engine to fire by "bumping" the starter repeatedly. I usually end up draining the battery but when the engine does fire it runs normally.

    Here are the diagnostics that I have performed:
    1) new battery cables-luckily my dealer took them back
    2) new OEM starter
    3) new solenoid
    4) new ECU flashed with the proper RIVA race tune
    5) new battery
    6) new starter relay

    I was about to test the fuel pump as that is one component I have never looked at since I bought the ski in 2014. This ski obviously has a lot of non stock hardware but I think the operating principles of a stock ski apply. My next guess is there is some voltage drop in the wire harness but I have no idea how to track this down.

  6. #6
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Quote Originally Posted by pro1200 View Post
    Oleg- You are describing the EXACT symptoms that my STX-15F race ski has. I have been fighting a starting issue for over two years now. My symptom is the starter stalls but I can sometimes get the engine to fire by "bumping" the starter repeatedly. I usually end up draining the battery but when the engine does fire it runs normally.

    Here are the diagnostics that I have performed:
    1) new battery cables-luckily my dealer took them back
    2) new OEM starter
    3) new solenoid
    4) new ECU flashed with the proper RIVA race tune
    5) new battery
    6) new starter relay

    I was about to test the fuel pump as that is one component I have never looked at since I bought the ski in 2014. This ski obviously has a lot of non stock hardware but I think the operating principles of a stock ski apply. My next guess is there is some voltage drop in the wire harness but I have no idea how to track this down.
    Have you ever tried to check the timing on the motor? I went through a lot of that when I was first setting up the map on my yellow racing and megasquirt ecu, I had the advance way too high and it put too much load on the starter when cranking over.

    Given that the ecu you are using is new and we have verified the tune on it, I wonder if there is something weird going on with a temp sensor that is out of range that kicks the timing up too much.

    Sean

  7. #7
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Quote Originally Posted by Oleg View Post
    Last time I was riding I noticed that the jet ski had trouble starting right before I put it on the trailer (luckly it was the end of the day). So I thought it was a low battery or bad starter. Now I've been trying to fix my 2006 stx15f for a while now and nothing seems to work. Battery voltage measures 12.6v. When I start cranking it, voltage to the engine drops to about 7ish volts and rotates the crank 2-4 times then seizes. I've jumped the ground/negative wire from the battery to the bolt of where the stator is and it cranked very nicely twice in a row so I thought I finally found the problem. Ordered a fresh negative wire, installed it and still, same problem. So I've again, jumped the negative wire from battery to stator and it didn't change a thing.

    Have you checked the positive terminals and cables? On the starter, I had good results by cleaning the ground terminal and mounting pads of the starter with a scotch brite pad and applying a thin layer of dielectric grease to the same surfaces. The connection from the starter motor needs to be as clean as possible.

    Starter - At first I thought it was the starter, so I replaced it with a brand new one, that seemed to fixed the problem. Then I parked them for the off season for a few months. I would periodically start the jet ski to make sure nothing is seized. I live in FL so nothing freezes. They sit outside with a cover. Then after a while it wouldn't start.

    When you replaced the starter, did you just pop the old one off and put the new one on? Being Florida, I am assuming salt water which means the mounting points and battery connections are probably corroded at least a little. The terminals especially are likely to get wet and wick water up the cable and corrode since they are just crimped and booted not soldered.

    Fuel pump - It wasn't starting because the fuel pump wasn't working, so I replaced it. Fuel pump pumps fuel fine now, no problems there. Also new fuel filter. But still it cranks very weakly.

    Unrelated to the cranking problem but, check the fuel pressure to make sure you are safe and that the regulator didn't get eaten.

    Spark plugs - new spark plugs. I noticed when the spark plugs are out, the engine cranks very easily and freely. All 4 plugs do spark when I crank the engine.

    This is pretty normal, when the plugs are out, there is basically no load on the starter. The starter is limited more by the voltage than the drag.

    Battery - I've replaced the battery and no luck. I've taken the battery from my other jet ski that works just fine and put it in this one, didn't fix the problem. I know the battery is working fine because it cranks the other jet ski with no problems and is fully charged.

    What is the age of the batteries?

    Solenoid - Took the starter solenoid from the other jet ski and installed it on this one - no change.

    Did you take the full cable set or just the actual solenoid?

    ECU - Took from other jet ski and no change.

    Not likely to be an ecu issue in your case.

    Voltage regulator - Same thing from other jet ski, no change.

    This really only comes into play when charging, while cranking the current into the battery is way lower than the current out to the starter.

    I'm now thinking that there is an open circuit somewhere and I have no idea where and don't know how to find it. So, I'm now thinking of replacing the whole wire harness and hope that fixes the problem but I'm worried that it might be a problem with one of the sensors. Also, my screen is sun faded and isn't working and I don't want to spend $500+ on a new dash.

    The harness will likely do nothing.

    Any tips will be greatly appreciated!

    Replied in red, just looking for more information.

    Sean

  8. #8
    steve45's Avatar
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    Pull ALL the connectors apart in the wiring harness and check for corrosion. I found a termination plug in my STX-15F that was corroded from laying in water in the bottom of the hull. That didn't cause a starting problem, except that it would discharge a battery in a day. Make sure all connectors are tied off well above the bottom of the hull. Check that all battery connections are CLEAN (scraped to bare metal) and tight.

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  10. #9
    Thank you for the tips. I will take it apart again and check all the connections and clean them up. What's a good/safe method of cleaning harness/sensor connections?


    What is the age of the batteries? about a year old

    Solenoid - Took the starter solenoid from the other jet ski and installed it on this one - no change.

    Did you take the full cable set or just the actual solenoid? just the solenoid.

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  12. #10
    steve45's Avatar
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    This thread shows what I found on an STX-12F harness: http://greenhulk.net/forums/showthread.php?t=281195

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