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  1. #1

    Msx 140 with misfire, been too long

    Hi guys,

    Im having trouble with my polaris msx 140 2003,
    There is a slight misfire at low revs and when i hit the throttle wide open it revs to 6000rpm then bogs the revs back up and bogs and keeps doing this.
    Sometimes on the hose i can get the jetski to hit the rev limiter but sometimes it will not hit the limiter and does the bogging..


    I have tried the following from another ski....
    emm
    Injectors
    Tps
    Coil and leads


    I have tested the following parts.
    Exhaust heat sensor
    Intake heat sensor
    Cps
    Stator ohms and volts
    Fuel pressure


    All this tested fine and made no difference when i swapped the parts over.


    The only thing is the compression is testing around 100 at all cylinders,
    Will this make a misfire?


    I am going to check the reed valves when i get chance, will faulty reed valves cause a misfire?


    There is not much else i can think of trying, is there anything im missing?


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Hmmm. Remove and inspect the temperature sensor on the exhaust. There is a known problem with the sensor wires sometimes getting pinched or abraded by the plastic exhaust section where it passes near the sensor. Look for damaged wires. Also check the sensor with an ohm meter. Reading should be very close to 1,000 ohms and stable as you flex the wires.

    It is easiest to remove the plastic 'hose' section to allow access to the exhaust temperature sensor.

    If the exhaust sensor is good, inspect the large rubber exhaust hoses. You may have a partial internal collapse or obstruction. There should not be any 'soft' sections in the exhaust hoses.

  3. #3

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    did you try a new set of plugs

  4. #4
    Looked at the reed valves, they are fine.
    Took the exhaust temp sensor out checked and tested whilst moving the wires.. Tested 1000ohms
    Checked the exhaust hoses... They have slight bubbling prob from heat, but they look to be fine.

    I also took the heads off to check the spray pattern of the injectors, i noticed the spark plugs were pointing with the open end open to the injector spray. Is this right? I thought i read somewhere that the open end should be away from the injector spray so it wont flood the sparkplug (or am i making this up? )


    I will try spark plugs next but i dont think there is anything wrong with them as they were supposedly changed just before i bought, and they are sparking.

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Don't worry about which direction the gap in the spark plug is facing.

    Make sure the correct spark plugs are installed. NGK PZFR6H only, no substitutes.

    Bubbles on the exhaust hoses? Have a look at the insides of those hoses.

  6. #6
    Ngk pzfr6h already installed, could there still be a problem with the plugs even though they are sparking?

    I ment bubbles on the inside of the exhaust hoses.. Probable normal, just looks like heat.

  7. #7
    Could there be a problem with the spark plugs even though they are sparking?

    Also my stator volts and ohms tested fine, do you think it is unlikely anything to do with the flywheel/stator.. I want to try and avoid taking this apart if i can.
    Or could there be something there i am unable to test for?

    Any help would be great, just really need pointers of what to check that could cause this as i cant think what else to check now..

  8. #8
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by FasterBaby View Post
    ... polaris msx 140 2003,

    There is a slight misfire at low revs and when i hit the throttle wide open it revs to 6000rpm then bogs the revs back up and bogs and keeps doing this.
    Sometimes on the hose i can get the jetski to hit the rev limiter but sometimes it will not hit the limiter and does the bogging..


    I have tried the following from another ski....

    emm
    Injectors
    Tps
    Coil and leads



    I have tested the following parts.
    Exhaust heat sensor
    Intake heat sensor
    Cps
    Stator ohms and volts
    Fuel pressure

    All this tested fine and made no difference when i swapped the parts over.

    ... compression is testing around 100 at all cylinders,
    Will this make a misfire?

    There is not much else i can think of trying, is there anything im missing?
    Is your compression tester accurate? What compression readings do you get from the other MSX 140?

    In a properly running engine it should easily reach the rev limiter with only partial throttle applied, and should idle smooth and stable at 1150 RPM.

    Things that have not been swapped from the working machine;
    Wiring harness
    Wire harness connectors (TPS, CPS, EMM, etc)
    Engine grounds
    Engine itself
    Fuel system
    Jet pump (bearings)

    Fuel pressure, what are the pressure readings with and without the fuel return hose clamped off?

  9. #9
    Just took the ski out today to try and have a fiddle with connections to see if it was bad connections.... No luck..

    Where would the earths be located that may cause me problems? I have only seen the one near the coils.

    Also i pulled the plugs after a while riding and pulled the plugs straight away, and noticed the plugs were bone dry and as clean as a whistle. They are supposed to be new plugs before i bought the ski, but i thought they were supposed to got a browny colour quite quickish? Does this point to it running lean?? Im not sure how these ski run normally as i have never seen it run right.

    I wish i took a picture of the plugs to post here, but now after running a few quick times they are fully blacked up again..

    I did the fuel pressure test again and it is... 21psi without return clamped and about 36psi with return clamped off.. Is this ok?

  10. #10
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by FasterBaby View Post
    Just took the ski out today to try and have a fiddle with connections to see if it was bad connections.... No luck..

    Where would the earths be located that may cause me problems? I have only seen the one near the coils.

    Also i pulled the plugs after a while riding and pulled the plugs straight away, and noticed the plugs were bone dry and as clean as a whistle. They are supposed to be new plugs before i bought the ski, but i thought they were supposed to got a browny colour quite quickish? Does this point to it running lean?? Im not sure how these ski run normally as i have never seen it run right.

    I wish i took a picture of the plugs to post here, but now after running a few quick times they are fully blacked up again..

    I did the fuel pressure test again and it is... 21psi without return clamped and about 36psi with return clamped off.. Is this ok?
    Fuel pressure numbers are good.

    There is an engine ground point on the left rear of the engine, on the side. Typically the heavy black battery cable is also there.

    There are ground wires throughout the wire harness, and multiple splice locations in the wire harness.

    Put a voltmeter on the White/Red wires, all injectors plugged in. What is the voltage reading when idling? Is the idle voltage stable?

    Does the voltage vary as RPM is increased? Does it change more as you reach above the 5500 RPM range?

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