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  1. #1
    Cadet
    Join Date
    May 2009
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    Huntsville, Al
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    22

    Default What are the symptoms of a bad coil?

    How will my 70hp Johnson run if I have one bad coil?

  2. #2
    Captain jbjennings's Avatar
    Join Date
    Jul 2007
    Location
    northwest Louisiana
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    3,917

    Default Re: What are the symptoms of a bad coil?

    A bad coil can go in and out and cause power surges when you get spark on the dead cylinder. It can just lack power totally because one cylinder is dead from no spark. OR, it can run fine, then when the motor warms up and thermal expansion causes you coil to go out, then lose power.
    I would think that the simple way to find out would be to check spark, then switch coils and see if the spark failure followed the coil. If you have intermittent spark because the coil goes in and out, it's harder to diagnose. Lots of times, you can pull the plugs and see which one is dirty/oily to find out which one isn't getting good spark.
    Good luck,
    JBJ

  3. #3
    Cadet
    Join Date
    Jun 2012
    Location
    Pass Christian, MS
    Posts
    2

    Default Re: What are the symptoms of a bad coil?

    I think i have a problem with my coils on my 175hp mercury. it starts first try cold but once it gets warm it wont start for anything. i know its been a long time since this thread has been posted on but if you could, could you give me a update on if you got it to work and what you did? thanks.d

  4. #4
    Chief Petty Officer
    Join Date
    Sep 2009
    Location
    Florabama
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    612

    Default Re: What are the symptoms of a bad coil?

    Quote Originally Posted by francistran7 View Post
    I think i have a problem with my coils on my 175hp mercury. it starts first try cold but once it gets warm it wont start for anything. i know its been a long time since this thread has been posted on but if you could, could you give me a update on if you got it to work and what you did? thanks.d
    Check out the Mercury section of iBoats:
    http://forums.iboats.com/mercury-mariner-outboards-25/

    You can check the coils by putting a timing light on the plug wires while running the engine in the same situation you normally experience the problem. Good ones fire steadily and bad ones miss or don't fire at all.

  5. #5
    Supreme Mariner kenmyfam's Avatar
    Join Date
    Aug 2006
    Location
    Belle River, Ontario.
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    14,253

    Default Re: What are the symptoms of a bad coil?

    Very old thread to go at again. Suggest you start a new thread stating the issue. Mod's will likely close this one.
    Marada 2100 Executive Series, 5 Litre V8 with Mercruiser Alpha 1 outdrive. 2007 K-Z Spree 260 RBH, all = a whole lot of family fun !!!!

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