Hitting on 2 of 4 cylinders

[turtle88]

I'm fairly new to boat repair, but I have experience in diagnosing mechanical issues. I have a 1982 50 hp Mercury 2 stroke 4 cylinder, my #2 & 3 cylinders are not working. I started at the end and have worked my way to the beginning. I checked each plug and plug wire for fire on the #1 coil, no problems there. I swapped my hot leads coming from the switch plate for the coils and were able to get each coil to fire individually. After returning all the wires from the switch plate to the coils to their original position, and I then swapped my hot wires coming from the trigger from #2 to #1, and now #2 works but #1 doesn't. I did the same with #3 & #4, same results. To me, I would think the trigger is the issue, but there isn't much information out there on triggers. Any suggestions?

 

[Midwestfields]

I think you're probably correct. You can ohms test the trigger and if you have a dva you can test voltage output.

 

[DavidMoore]

A shorted stop diode in a CDM in either 1 or 2 would cause both 3 and 4 to stop firing.

Never done this myself but I suppose its possible to eliminate a defective CDM from being the issue. After checking the 4 pin plugs a nice and clean and there is nothing that could cause a short. Try this

Swap the CDM from cyl 1 with cyl 3 and test, then swap the CDM from cyl 2 with cyl 4 and test.

If during either test cyl 3 and 4 start firing and cyl 1 and 2 stop firing you just swapped a defective CDM.
If the problem remains the CDM's are OK and the problem is somewhere else.

 

[Faztbullet]

This motor don't have CDM modules.....