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Testing ignition coils

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whaler_warner

Contributing Member
I recently removed the coils from my M90a to test and following the FSM the primary coils all tested within specs but secondary coils all measured in the 6400ohms range against specs quoted of 3600-4800? I triple checked each coil and got the same result.

are these specs ok? I’ve had problems with power dropping when motor is warm and after high speed/load running which is why I wanted to check them hoping to find maybe one out of spec?
 
The secondary side of the coil is near infinite -- very high resistance. A lot depends on the specific ohm meter you use. I would consider those coils OK. I would also check the exciter and the 3 pulsers. Tough one to troubleshoot, as you need to check this stuff when you are having the malfunction, so you need to get it hot, and then immediately check the readings.
 
Thanks Paul,

All i can do is really test one thing at a time and try and rule each thing out until I found the culprit, intermittent faults are always the worst! I have purchased some spark plug testers and hoping to get back out on the water in the next couple of weeks, fresh fuel, fresh plugs and see how it runs if power drops I can fit the testers and have someone look whilst under load and visually check I have spark.

One theory I had is that when I got the motor the oil tank was removed and I couldn't find where to plug the sensor back into, when removing the coils I found the wire under the cover and I suppose this could be grounding which would put the motor into limp?

Something else which was weird was when removing the cover (which houses the solenoids/connections) when I undid the bolt holding the cover on it was sparking which I thought was strange (and worrying) as there shoudnt be anything live so quickly disconnected the battery. ​
 
Yes, intermittents are the worst. If you trigger the low oil sender wire, you should get an indicator light (if your tach has that). Low oil sensor does not limit RPM on the 90A. Assuming the carbs are perfect, and the linkages are properly synchronized, I would look at ignition components. A single pulser or coil or plug will cause a misfire, but a failing exciter will affect all 3 cylinders.
 
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