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How to check and test a Mercury Mariner Coil

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  • How to check and test a Mercury Mariner Coil

    The technician at CDI gave me some pointers on how to check a coil and I thought I would pass them on.

    The first step is to do a Ohms test to see if the coil is good before going on to the visual internal ferrite core inspection.

    Meter Test:

    1. With your ohm meter, measure the coil ground to the secondary (where the spark plug wire goes). (See attached photos)

    2. See if it is around the 1KΩ or 1000Ω range. If so then go on to the visual inspection.

    Visual Inspection:

    Warning: Do not put a lot of pressure with your fingers on the top (where the brass screw threads are) and bottom of the ignition coil. You may snap the fragile Ferrite core inside.

    1. Gently peel back the rubber protector and take it off of the ignition coil.

    2. Check to see if there are any noticeable cracks. If so, replace the coil.

    3. If no visible cracks are noticed then check to see if the area where the two ferrite parts meet are loose. If so you need to see if one or both have lost the silicon bond
    that helps to keep them from separating too much.

    4. The string stranded packing type of tape is used to hold the two ferrite cores together. Sometimes this gets dirty and looses its adhesion so the technician recommended to add the silicon to hold the ferrite like before and to add a couple of Super Glue Gel drops where they ferrite core halves meet. You could also add the string tape if you would like for added comfort.

    5. Carefully put the rubber protector boot back on and hope it works!
    Click image for larger version

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  • #2
    Re: How to check and test a Mercury Mariner Coil

    Thanks for the info. I'm trying to track down a bogging problem and the coils were something I wanted to look at. The pics are very helpful.


    • #3
      Re: How to check and test a Mercury Mariner Coil

      I appreciate the comment ... I realized that sometimes we can't find what we are looking for in the forum so if we could document our experience then it may help others. Usually these units do not go bad but when I took a look at mine I had five out of six with ferrite and contact corrosion problems. My coils read fine (this is the part that rarely goes bad). I ended up getting six "better than mine" used ones off of a auction site about the price of a new one. Of course if you follow the same path as I did you will need to check your newly purchased "used" coils so you don't create more headaches. Good luck!


      • #4
        If the coil is bad what will the OMHS meter read? I will be using a fluke to test them. Basically what will tell me its bad?


        • #5
          Sign up today
          Originally posted by nolawall View Post
          If the coil is bad what will the OMHS meter read? I will be using a fluke to test them. Basically what will tell me its bad?
          The range ( +/- 10% or 900 to 1100 ohms) is given above in this old, inactive post. Please start a new topic with your question. Why? Because none of the posters visit any more so it's hard for them to answer your question.

          Please, no PM's (Private Messages) regarding boat/engine problems.
          That is what the forums are for.
          Only forum/moderator issues will be answered in PM's.