2003 Mercury XR6 Serial 0T666017

[xcoach]

I took the grandkids out a month ago, motor ran great to first two spots. Cranked up and had a bad miss, limped back to launch. I replaced the plugs and fuel hose and finally got out with them again today and the exact same thing happened again. The miss appears after the motor has warmed up, not cold. I’m thinking maybe a CDM module has gone bad, unsure of what else it could be. Since it only happens after it’s warm, unsure how to check those except to idle on the muffs awhile, then touch each plug to a bolt and see if there is spark. Anybody have ideas or suggestions of what I could be missing or a better way to check those.

[EuropeanAM]

Take a timing light out on the water with you. When the problem occurs, remove the cowling. Did engine start running better just because you removed cowling? If so... there's a specific list of possible items.

If not, clip the timing light lead to each plug wire, one at a time, and watch for a steady flashing pattern. No pattern or bad pattern? Spark plug, Wire, CDM (may not be the one without spark), poor grounds, Trigger or even the ICM.

[xcoach]

Thank you Don, will do.

[lpugh]

Be sure there are no under cowl water leaks (look for whites residue left behind)
Use a heat heat gun to warm coils and drivers one at time running on the muffs to see if they fail
Inspect plugs carefuly for fouling, carbon tracks or cracks
Using fine mist spray bottle wet down all the secondary ignition parts, coils, wires and plugs. No change should ocur if all is good. look for any arching to a ground path
This you can do at home and hopefully find the issue without on the water testing

[xcoach]

Great info, thanks for sharing, going to check CDM’s, if they test ok, gonna to let airport marine check all other related electrical parts, beyond my capabilities. Funny you mentioned heat gun, got one coming today.