Results 1 to 7 of 7
  1. #1

    Default " My 1986 115 seems to have on

    " My 1986 115 seems to have one cylinder that does not work when the engine is cold. After about 15 minutes or so you can feel the power gain or if its driven for a few minutes, shut off for 10 minutes and restarted, it runs good. Compression is 115-120 in all cylinders. I checked the spark when cold and the top 3 cylinders aren't sparking, the bottom three do but there is no way its only running on three when its cold. I figured it was only the top giving me problems. The coils look like their bundled in three. Is it possible all three are intermitantly bad? any suggestion would be appreciated. "

  2. #2
    Join Date
    Nov 2005

    Default " I can't say exactly what

    " I can't say exactly what's going on there, but yes, I believe there is a coil for every cylinder, bundled in three. There are also two switchboxes (black boxes before coils) that distribute the power to those coils and a problem could very well lie there. Also, just for kicks, there is a terminal on each black box that is used to kill the ignition. This is done by applying ground to it. First thing I'd probably do is be sure that one of those terminals isn't being grounded somehow, it's an easy check and would surely kill ignition to exactly 3 cylinders.

    Next I'd swap the coil bundles or the switch boxes and see if the problem swaps cylinders. If it doesn't swap cylinders, I'd swap the next item (coils or switch boxes, whatever was not checked). I'm just a hack, but I think that if it was a coil problem, it'd probably just be one cylinder and not all three. Obviously wiring could be a problem as well. If it turns out to be none of the above, I'd look into the source of power, stator and trigger etc.. Hopefully it will stay broken long enough for you to figure out what it is, things like this tend to temporarily fix themselves. Tell me how it goes,

    Jon "

  3. #3

    Default Put a timing light ( or t

    Put a timing light ( or two if you have them ) on the spark plugs . Observe the flash and see if there is spark on all cylinders.This way you can use the timing light like a scope.

  4. #4

    Default " Thanks for the quick respons

    " Thanks for the quick response guys. I also suspected one of the switch boxes at first but when I was checking connections I noticed cylinders 1 & 3 were fed by the top box and 2 was fed from the bottom one and I couldn't get a spark on 1,2 & 3. I plan to try all your suggestions on the weekend and I'll let you know what I find. Thanks again. "

  5. #5

    Default I found the battery dead this

    I found the battery dead this weekend so I took the battery out of my fishing boat and it fired up on all 6 (the timing light is a great idea). I'm wondering if a faulty battery could have been causing the problem.

  6. #6
    Join Date
    Nov 2005

    Default " Eric, No, I'd sa

    " Eric,

    No, I'd say as long as the battery was turning it over fast enough when you were checking spark, it could not cause the problem. More likely is that something is going wrong that is preventing the battery from being charged. I'd keep trouble-shooting that, it probably just temporarily fixed itself.

    Jon "

  7. #7
    Join Date
    May 2011
    Peteborough, Ontario, Canada

    Default Re: 115 Mercury inline 6 problems

    If no spark on 3 cylinders will be Stator, or bad switch box


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