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  1. #1

    780 MFD blows fuses

    New to PWC. I have an opportunity to buy a 95 SLX. Looks and runs like new but blows fuse on MFD. Replace and it is ok for a while. Any ideas or suggestions? Guy wants $800 with a trailor.


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Welcome to the Hulk!

    1995 SLX780, I presume.

    I would suspect an intermittent short in the wiring from the electrical box to the MFD, or something is loose or shorting inside the electrical box.

    As long as everything else electrical still works, even when the MFD fuse is blown, then you probably don't have a big problem. Check that the battery voltage when the engine is running is right around 14 volts, and stays close to 14 volts as the RPM rise.

    Of course, you still need to do all the due diligence checking when buying a used PWC. Engine compression, hull condition, impeller wear, and so on.

    There are some common updates and maintenance items these Fuji engine models, including replacing the fuel lines. A few searches on here will find them for you.

    The trailer; if the tires are more than a few years old, plan to replace them, even if the tread looks good. Old trailer tires can look good on the outside, but still be weakened and failure prone at speed. Some guys get away with ancient tires, but I don't recommend it. Check the winch straps for aging and fraying, and look the whole thing over for cracks in the frame, rusted bolts, damaged coupler parts (look underneath the coupler), etc. Make sure the trailer electrical is good - all the lights are intact and actually work, wires are not frayed, or a taped up patch job.
    Last edited by K447; 07-30-2008 at 09:54 AM. Reason: Trailer notes

  3. #3
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Welcome to the Hulk.
    I'd say its a good deal if the boat is in good condition and engine has good compression, even if the mfd is screwed.

  4. #4
    Thank you. All good points, and yes to the 95 slx780. What should the compression be?
    Last edited by watchn; 07-30-2008 at 09:49 AM.

  5. #5
    Lake Mead Bum & BTLS Mark starflight's Avatar
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    Quote Originally Posted by watchn View Post
    Thank you. All good points, and yes to the 95 slx780. What should the compression be?
    120-130 would be normal.

  6. #6
    Quote Originally Posted by K447 View Post
    Welcome to the Hulk!

    1995 SLX780, I presume.

    I would suspect an intermittent short in the wiring from the electrical box to the MFD, or something is loose or shorting inside the electrical box.

    As long as everything else electrical still works, even when the MFD fuse is blown, then you probably don't have a big problem. Check that the battery voltage when the engine is running is right around 14 volts, and stays close to 14 volts as the RPM rise.

    Of course, you still need to do all the due diligence checking when buying a used PWC. Engine compression, hull condition, impeller wear, and so on.

    There are some common updates and maintenance items these Fuji engine models, including replacing the fuel lines. A few searches on here will find them for you.

    The trailer; if the tires are more than a few years old, plan to replace them, even if the tread looks good. Old trailer tires can look good on the outside, but still be weakened and failure prone at speed. Some guys get away with ancient tires, but I don't recommend it. Check the winch straps for aging and fraying, and look the whole thing over for cracks in the frame, rusted bolts, damaged coupler parts (look underneath the coupler), etc. Make sure the trailer electrical is good - all the lights are intact and actually work, wires are not frayed, or a taped up patch job.
    Guy is coming today. Check voltage at the battery?

  7. #7
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by watchn View Post
    Guy is coming today.
    Check voltage at the battery?
    Always check battery voltage and charging voltage right at the battery.

    A healthy battery will be right around 12.5 volts just sitting, if it is fully charged (12.8 volts for an AGM battery).

    During cranking, battery voltage should stay above 11.0 volts. 11.5 volts is even better.

    Disconnect the battery, and have a good look inside the electrical box. Might see a loose terminal or wire that is blowing the fuses.

    Also look for abraded or worn wires that might need insulating, especially around the engine, and where the wires enter the box from the outside.

    Inside the electrical box should be dry, with zero rust or corrosion on the terminals. The seal around the rim should also be intact.

    Back to the machine itself.

    The engine should crank smartly when you press the button, and should light up fairly quickly (with choke, if the motor is cold). If it takes a LOT of cranking to get it going, then something is not as it should be.

    Don't run it for more than 10-15 seconds without water cooling.

    When it does start, charging voltage should jump right up to around 14.0 volts, and stay there as RPM rises.

    Good luck!

  8. #8
    Thank you. Two ? Radio Shack does not have 1/4 volt mini fuses. They do have a .315. OK? Next, do I need to lift the black box from the top of the battery and crank it then to measure voltage? There is a warning sticker inside the compartment that says not to do that.

  9. #9
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by watchn View Post
    Thank you. Two ? Radio Shack does not have 1/4 volt mini fuses.

    They do have a .315. OK?

    Next, do I need to lift the black box from the top of the battery and crank it then to measure voltage? There is a warning sticker inside the compartment that says not to do that.
    Mini-fuses?
    I think it is a standard 1/4 inch diameter, 0.25 Amp glass fuse, Radio Shack part number 27.1002

    In a pinch, the 0.315 Amp fuse would be OK, I suppose. Replace it with the correct 1/4 Amp fuse when you can.

    When checking battery voltage, you may need to prop the electrical box out of the way. Use a towel or something so it doesn't touch the battery posts.

    Just be sure it doesn't fall against the drive shaft or engine, or contact the battery. An extra set of hands can be helpful, to hold things while the engine is cranked, and the meter is watched.

    And be sure to have the plastic battery cover in place before you re-position the electrical box back into place.
    Last edited by K447; 07-31-2008 at 10:07 PM.

  10. #10
    Thank you. I haven't taken the box apart yet to see what size the fuse is.

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