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Looking for help in testing Merc 55HP trigger coil

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  • Looking for help in testing Merc 55HP trigger coil

    Im wondering if someone can provide me with the resistance values for checking a Merc 3cyl. trigger coil. The outboard is missing quite badly under load but idles great. Ive checked the resistance across the purple, brown and tan wires and they are all fairly close, from 3.84M Ohms to 5.02M ohms. Thank you for your help!

  • #2
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    Are you sure it's ignition and not fuel? Not much to go on.....55 hp Merc 3 cyl. Do you have 3 separate trigger circuits whereby you could verify a cylinder if functioning and then move that circuit to another cylinder and test it there and on to the third cyl.? Idle has no fuel requirement to speak of. WOT needs all the supply system can give it. Bad fuel, cracked fuel lines, dirty filter possibly contaminated by pieces of deteriorated fuel lines, dirty carbs all can contribute to poor running at higher rpms.

    On fire I found a battery operated automotive timing light handy. Hook the clip to a sparkplug lead and put the engine through it's paces. If it maintains fire on all cylinders go after your fuel system. If not, chase the one that isn't firing properly. Resistance checks are a place to start, but a high voltage problem in your ignition high voltage circuit(s) only shows it's colors when high voltage is present....aka engine running.
    If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.