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I'm stumped! From last season into spring startup, I've gone through 3 coils on my port and 4 on my starboard engine. These are on Mercruiser 454s with Thunderbolt IV distributors. The boat was running kind of rough when I bought it and the plug wires were arcing so I replaced plugs, wires. The coils started having issues, one due to water damage and the other no spark. I replaced both with Sierra equivalents. Long story short, I have gone to a cheaper version (AA Ignition) and I am still having problems with spark jumping under the boot to the terminals, or a sudden no spark when the engine has been off. Here's what I know; the plugs that I used were factory recommended. The manual said to gap the at .040 which is what I did. I have later noticed that the label on the air breather cover calls for a gap of .035. I can't imagine that .005 would make that much of a difference. As far as the coils go, my primary resistance is 1.5 ohms and the OEM coil calls for .6 - .8 ohms. Could that do it? I appreciate any feedback, Dave

https://www.perfprotech.com/blog/tech-a ... rol-module
https://forums.iboats.com/forum/engine- ... ition-help
http://www.boatfix.com/merc/Bullet/83/83_24.pdf

Have you seen these articles. Could it be the harness?

If the gap in the plug is open too much, you might get a weak spark if you are not putting out enough voltage. When looking through some of the articles I came across when researching this, others say the gap should be .35, and that .45 was too large of a gap. But even with that, I doubt that is your issue.

Thank you Tony!