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  1. #1

    Blocked exhaust/mysterious msx.

    Hi guys, just wondering what I am actually looking for with regards to a blocked exhaust on a polaris msx 140?
    I have been told to look for any blockages, but i cant see anything obvious, will it be a lump of of something or is it when the packing in the waterbox goes bad?

    Just any help on what to look for would be great.

    its an ongoing problem were as my polaris is fine on start up and ticks over fine but is misfiring when I rev slightly and on the water i can feel it does a slow judder/ hesitation thing where it starts to go and then slows and starts to go and slows again continues to do this and wont go over 40mph..

    I have tried.
    EMM
    injectors
    spark plugs
    pistons
    top end gaskets
    coils
    tps
    and have tested
    exhaust sensor
    air sensor
    cps
    injector voltage
    injector voltage drops slowly when switched off
    (all fine)

    i have tested the stator when cranking and this is fine, but i am wondering if it may break down as the motor spins faster when i rev?? If so do you know how to test the stator whilst the ski is running?

    Im stuck now as you can see i have tried a lot of stuff and would really appreciate any help anyone could give me!


  2. #2
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    I see one glaring thing missing from your list. You need to check your fuel pressure. Sounds like the classic regulator fell off symptoms.

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by FasterBaby View Post
    ...

    I have tried.
    EMM
    injectors
    spark plugs
    pistons
    top end gaskets
    coils
    tps
    and have tested
    exhaust sensor
    air sensor
    cps
    injector voltage
    injector voltage drops slowly when switched off
    (all fine)

    i have tested the stator when cranking and this is fine, but i am wondering if it may break down as the motor spins faster when i rev?? If so do you know how to test the stator whilst the ski is running?

    Im stuck now as you can see i have tried a lot of stuff and would really appreciate any help anyone could give me!
    Fuel pressure check, as per Bryan.

    What do you mean by 'tried' all those things?

  4. #4
    Ooopsie,
    also tested fuel pressure, which is ok
    checked and the regulator is in place..

    k447, i tried with known working parts.

    what do i look for when looking for a blockage in the exhaust?

    and have you ever heard of the O rings going on the fuel T connections that push into the injectors?
    im thinking the o rings might be letting air in with the fuel?? (Just guessing)

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by FasterBaby View Post
    what do i look for when looking for a blockage in the exhaust?

    and have you ever heard of the O rings going on the fuel T connections that push into the injectors?
    im thinking the o rings might be letting air in with the fuel?? (Just guessing)
    The fuel system is supposed to have something around 23 PSI of pressure. Any o-ring leaks at the injectors would be leaking fuel OUT, not letting air in.

    Best way to confirm no blockage in the exhaust system is to just take it apart and inspect each piece. The large rubber hoses should NOT have any significant blisters or noticeably soft areas on the inside. Overheated exhaust hoses can delaminate and partially collapse. Sometimes this is noticeable from the outside by feeling for soft areas, sometimes you have to look inside the hose to be sure. Normally the hose(s) closer to the engine overheat first/more.

    On the MSX 140 it is hard to get at the hose connection to the through-hull exhaust fitting. Take the bolts off from the outside and you can peer in from the outside. Use a good flashlight. Look for signs of creature nests too.

    The MSX waterbox has some internal baffles but you can still inspect via the openings. Note that there is a water hose connection down very low on the front of that MSX 140 waterbox. Very stubby 3/4" hose, tricky to get off and back on. If I was suspecting blockage I would take the waterbox right out so I could shake it and get a good look-see inside.

    Measure injector voltage with all injectors plugged in and engine running. White/Red wire voltage relative to engine ground. What is the voltage (and voltage change) as the RPM rises?

    Connect inline spark testers to all three spark plugs. Verify spark is consistent to all three as engine RPM rises.

    Does the engine rev smoothly when out of the water?

    Any trouble codes from the EMM when using the Simple LED code reading method?
    Last edited by K447; 01-29-2014 at 11:04 AM.

  6. #6
    Injector voltage is fine and constant even through the misfire and juddering.
    it holds and drops slowly when turned off.

    k477 what exactly am i looking for when im looking in the exhaust? Am i looking for anything that could be stopping exhaust fumes coming out the exhaust, like bits of rubber of the pipes? Or something else?
    And what do you mean by blisters on the rubber exhaust pipes? Can this really cause a problem? If so could you explain how so i can check if this is my problem.

    i have seen small blisters on the inside of one of the rubber pipes quite a few little popped bubble things at the end about the size of a LED bulbs.
    but when i squeeze the pipe, it seems strong enough and doesn't collapse.

    Also i have taken the exhaust off but left the exhaust manifold on, and i started it and gave it a quick rev (i know i shouldnt) and it still had the same misfire.

    the symptoms are the same in and out of the water, hooked up and not hooked up to the hose.

  7. #7
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by FasterBaby View Post
    Injector voltage is fine and constant even through the misfire and juddering.
    it holds and drops slowly when turned off.

    k477 what exactly am i looking for when im looking in the exhaust? Am i looking for anything that could be stopping exhaust fumes coming out the exhaust, like bits of rubber of the pipes? Or something else?
    And what do you mean by blisters on the rubber exhaust pipes? Can this really cause a problem? If so could you explain how so i can check if this is my problem.

    i have seen small blisters on the inside of one of the rubber pipes quite a few little popped bubble things at the end about the size of a LED bulbs.
    but when i squeeze the pipe, it seems strong enough and doesn't collapse.

    Also i have taken the exhaust off but left the exhaust manifold on, and i started it and gave it a quick rev (i know i shouldnt) and it still had the same misfire.

    the symptoms are the same in and out of the water, hooked up and not hooked up to the hose.
    Sounds like exhaust blockage is not the problem.

    Things that have not yet been changed, or checked (in no particular order);
    Wire harness(es)
    Wire harness grounds
    Wire harness connectors and splices
    Stator (visual)
    Flywheel (visual magnet inspection and TDC timing, woodruff key)
    Capacitor
    NGI display (unlikely to cause misfire, but I suppose anything is possible)
    TPS connector or wire harness
    Spark plug wires (Ohms, internal wire damage)
    Intake reeds
    Crank shaft seals (front and rear)


    Anything else?

  8. #8
    Just a few more questions and i will have another go cheers )))

    1) can there still be a stator fault after i have done a test at cranking speed? Could it break down when the engine spins faster? If so is there a way to test this

    2) could there still be a prob on the temp sensors, even though they have tested ok with multimeter?

    3) how easy is it to get the engine out with just man power (no engine lift) .. Can two guys lift it out?

    4) i have done the test were i watched the voltage on the injectors when i turned off the jet ski and it held the voltage and slowly dropped... Does that mean the capacitor is working fine? Or does it do another job too?

    5) thanks alot

  9. #9
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by FasterBaby View Post
    ...

    1) can there still be a stator fault after i have done a test at cranking speed? Could it break down when the engine spins faster? If so is there a way to test this
    Usually injector voltage is the tell. If injector voltage is stable and right at the 45 volt level, then the stator is probably OK. That said, sometimes weird stuff happens.

    2) could there still be a prob on the temp sensors, even though they have tested ok with multimeter?
    Possible. Temp sensor can be unplugged for test purposes. If engine still runs badly the sensor is probably not the 'main' problem.

    3) how easy is it to get the engine out with just man power (no engine lift) .. Can two guys lift it out?

    4) i have done the test were i watched the voltage on the injectors when i turned off the jet ski and it held the voltage and slowly dropped... Does that mean the capacitor is working fine? Or does it do another job too?
    Capacitor is probably fine. Forgot that you mentioned checking the voltage decay.
    ...
    Engine removal can certainly be done by hand without a hoist. The more stuff you unbolt from the engine the less weight you have to lift (exhaust/intake, starter motor, PTO coupler, etc)

    A simple and small chain hoist just makes it much easier. And less risk to fingers and engine/fiberglass if something were to slip.

    I use a small 500 pound chain hoist. The engine weight is not the main reason (although it is heavy enough that the hoist lifting is appreciated). What the hoist really does is make it much easier to twist and wiggle the engine out and then back into the hull. When you need to check clearances, change the engine angle, or move a hose/cable/fingers out of the way the engine just floats in the air on the chain until you are ready to proceed.

    The chain hoist also makes it possible to leave more hardware attached to the engine and still lift it out, since you can maneuver it around more easily.

  10. #10
    Cheers, where do you hook the chain to on the engine, to use the chain hoist?

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