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  1. #1
    john zigler's Avatar
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    97 SLT 780 limp mode??

    can some one tell me, when a ski is in "limp mode" can you see the CDI limit the RPMs with a spark tester? i cannot remember on the polaris machines.....

    here is what i have. a 97 SLT 780. will not rev out on the trailer. it "sounds" like the rev limiter is kicking in early. it has good compression, i can see the carbs spraying fuel. ( i even tried spraying fogging oil, as extra fuel). i have opened the electrical box, unplugged the grey, tan, and blue wires. i have unplugged the MFD ( which is working fine), ect.

    thing is, i have three spark testers on the wires, and i cannot see it break, or loose spark when you rev it out. ( like i can on the seadoo's).

    the customer, had cut the oil sender wires, and tied the blue, and black together. ( thinking it was the oil) so when the machine came in, it DID have the oil light flashing.

    it has been a while since i have had a machine in limp mode, and i have NEVER had one that did not come out if it, by unplugging the grey wire.

    i am now thinking the CDI is bad. i do not have any here at this time, to try. i didn't want to have to buy one and find this is not the issue. any one have any other idea's?

    zig


  2. #2

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    John
    We had one doing the same thing it ended up being a bad stator even though it ohm'd out ok

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    You should see the spark testers pulse dark and then back on (all of them together) as the RPM limiter cuts in and out.

    If the stator or CDI has just gone weird then the spark testers may show no pattern at all, or something not consistent with normal RPM limiter cycling.

    Make sure the correct resistor spark plugs are installed. Non-resistor spark plugs can cause electrical interference which confuses the CDI.

  4. #4
    johnsonmtz's Avatar
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    Quote Originally Posted by john zigler View Post
    97 SLT 780. will not rev out on the trailer. it "sounds" like the rev limiter is kicking in early. .....i have opened the electrical box, unplugged the grey, tan, and blue wires. i have unplugged the MFD ( which is working fine), ect.

    thing is, i have three spark testers on the wires, and i cannot see it break, or loose spark when you rev it out. ( like i can on the seadoo's).

    the customer, had cut the oil sender wires, and tied the blue, and black together. ( thinking it was the oil) so when the machine came in, it DID have the oil light flashing.
    Try throwing one of your spare oil sending units on the oil sender wires, tie the float at the top, and see what happens. That should be a quick easy way to eliminate the low oil warning.

    I've never tested a machine while in LIMP mode so I don't know exactly what you should expect to see on the spark tester. Next I'd say test crank index and throw a timing light on the flywheel. Sheared flywheel key maybe?

    I don't see anywhere in the manual that says the low oil triggers LIMP mode and it only says the RPM is limited to 4200.

    KJ

  5. #5
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    John, do you have a 750 CDI you can try real quick?

  6. #6

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    Info from service manual

    Here is some info I pulled out of my service manual, I hope this helps get your machine up and running, from what I read it did not seem that low oil causes the machine to go into limp mode. Also, I thought I remember at some point there was a way through the MFD to dissable Limp mode for 5 mins if you held one of the buttons, maybe someone else can confirm. Good luck

    Click image for larger version. 

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ID:	239364Click image for larger version. 

Name:	electrical troubleshoot chart.jpg 
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ID:	239364ELECTRICAL
    RPM Limiter Circuits
    RPM Limiter Function ( 1997 SL780, SLT780, SLTX, SL1050)
    An RPM limiting system (see models listed above) protects the engine by electronically limiting RPM in the event
    of engine overheat. This feature is designed to help prevent engine damage due to engine overheating.
    Engine Overheat
    If the engine overheats, the thermal switch becomes conductive and provides a ground path for the tan wire leading
    from the COl module and the Mult-Function Display. The Multi-Function Display will display a "HOT" warning
    message, the warning light will flash, and the engine RPM will be limited to approximately 4200 on 780 models,
    or 4500 on 1050cc models. A circuit within the COl senses the ground path connection and activates the limiting
    function. See diagrams below.
    Low Fuel
    No low fuel limiters are present on these models.
    Important Note: When the engine overheat circuit has caused the system to limit , it will continue to limit until
    both of the following conditions are met:
    1. The problem that caused the initial limiting must be corrected (cool engine);
    AND
    2. The operator must momentarily release the throttle and allow the RPM to fall below 4200 or 4500.

  7. #7
    john zigler's Avatar
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    Quote Originally Posted by xlint89 View Post
    John, do you have a 750 CDI you can try real quick?
    you know, i might have a 750 one here. good idea kev.

  8. #8
    john zigler's Avatar
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    Quote Originally Posted by K447 View Post
    You should see the spark testers pulse dark and then back on (all of them together) as the RPM limiter cuts in and out.

    If the stator or CDI has just gone weird then the spark testers may show no pattern at all, or something not consistent with normal RPM limiter cycling.

    Make sure the correct resistor spark plugs are installed. Non-resistor spark plugs can cause electrical interference which confuses the CDI.

    i know on any other machine, that i have had ignition troubles, you can easily see it in the spark testers. that is what kind of made me wonder on this particular unit. i cannot "see" any break in the spark, yet i can "hear" it, when it is running. sounds just like the rev limiter.

    new plugs, and cutting back the wires, was one of the first things i tried. ( always do).

  9. #9
    john zigler's Avatar
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    Quote Originally Posted by 785 lugs View Post
    John
    We had one doing the same thing it ended up being a bad stator even though it ohm'd out ok


    THIS is exactly what i was afraid of...........

    thank you bob. zig

  10. #10
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    I have a 750 cdi here if you need to borrow one for a bit.....

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