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  1. #1
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    Jul 2013
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    Austin, Tx.
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    Something grounding out

    2008 250 ProXS
    Serial 1B719014

    Finished up my 400hr service and put a new prop on that I wanted to test out. I left the house with the cowlings off because this weekend I was going to tear into the intake and check the reeds per the service manual. I know.....dumb thing to do.....go run the engine without the cowlings where water can get inside and potentially cause a catastrophe. I was only intending to run up the lake a short distance and back down and head home. Boat ran fabulous! On the way in I decided to check out a small cove and make a few casts before putting it on the trailer. I came in a little hot and upon shutting down some water rushed up and came across the engine. Not enough to run up inside the plenum, but enough the electrical got wet. I shut engine down and fished for a few minutes. When I went to start it, I ran about 2 seconds and shut off. It would turn over fine so I figured I pulled my kill switch. Nope......so I started checking fuses. I found a 20 amp fuse (#4) in the main harness popped. I replaced it and it started and ran about 2 seconds and shut off again. Today I unplugged most every connection and sprayed them out with an air hose and reassembled. Upon replacing the fuse again, when I turn the key on, it still pops the fuse.

    Any idea where to start looking?

    Obviously I won't be making that bonehead decision again to run without cowlings.
    Thanks

    EDIT....so I went out and did some testing. I unplugged every coil and 1 by 1 plugged them in and then hit the key starting from the bottom. I got to the second to last one (#1) and it popped. So I replaced the fuse and unplugged it and tested the last coil and it did not pop. So now I decided to move the bad coil to isolate if it was the coil or the wiring leading up to it. I swapped #1 for #2 and plugged everything in.......The damn thing didn't pop. The engine starts and runs. So now my question is.....if a coil is going out, will it be intermittent? I'd hate to replace it and it not be the issue. Thoughts?
    Last edited by Chris Coufal; 12-11-2018 at 09:00 PM.

  2. Member low slung cruiser's Avatar
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    LKG, LITTLETON, NC
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    #2
    Sterling 22XS / Mercury Pro XS V8

  3. Member
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    Mar 2010
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    Mooresville, NC
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    #3
    This is most likely a coil that has crapped out. It probably took out the fuseable link as well. I would say it is not related to the water... or could be related to the water. The high water content could have grounded a coil out and screwed it up. The fuse blows to protect everything else.

  4. Member
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    Jul 2013
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    Austin, Tx.
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    #4
    Just found this in the manual......so I guess I'll test them 1 by 1.

    rsz_120181211_162651.jpg

  5. Member
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    Mar 2010
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    Mooresville, NC
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    503
    #5
    Most of the time when a coil goes, it will bulge out or deform. This may help in locating it.

  6. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    Apr 2008
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    Greenville, SC (US)
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    #6
    I've seen many failed coils with ZERO visual indicators- so don't depend on that. Certainly LOOK (sometimes the best diagnostic tools are either side of the nose), though.

    Tests outlined in the manual are a good method- also inspect the connectors in the coil AND the harness for any signs of melting.

    Several other devices back there with fused circuits that can short from water... I will however strongly caution against the "blow another fuse method".

    Shorted coils can cause damage to the PCM, so it's best to diagnose the circuits and locate the problem without blowing ANY additional fuses, if at all possible.

    If the Coil Driver Circuits in the PCM blow, you will know (no spark no matter what).


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