Mercury 100 hp 2 stoke 2+2 won't kick in other 2 cylinders

[paulywally]

Hey guys,

I am having trouble with a 1999 Mercury 100 hp 2 stroke out board with the 2+2 system, this is the system where 2 cylinders don't contribute below ~1800 rpm. Serial number 0g881962.

The problem I am having is that I lost spark on the bottom two cylinders that are supposed to kick in at 1800 ish rpm. If I try to run above 1800 they don't start sparking, and foul the plugs. I can't find the shop manual in the faq sticky, the one on there for 100 hp only goes to 1997 I think and doesn't even mention the 2+2 system. Do you guys have any information on how I go about testing this ignition system? I'm guessing trigger coil but I'm not exactly sure how this systems works and I have no values to compare too.

Thanks a lot for the help.

 

[Faztbullet]

Sounds more like a CDM module is bad, go to CDI electronics and get the troubleshoot manual and test them. As #1 can be bad and sparking but affect other and cause them to misfire or not fire.

 

[racerone]

The bottom 2 cylinders spark all the time.--------It is carburetion that kicks in above 1800 RPM or so.

 

[tryn2rtre]

Based on the fact that they are supposed to spark all the time and it was stated that they foul, it seems that your motor is not sparking and your carburetor is triggering properly. It sounds like coils or a power pack maybe.

 

[paulywally]

Great suggestion. I love their trouble shooting manual but there is nothing in there on the 2+2 system. Already checked and emailed them.

Sounds more like a CDM module is bad, go to CDI electronics and get the troubleshoot manual and test them. As #1 can be bad and sparking but affect other and cause them to misfire or not fire.

 

[paulywally]

The bottom 2 cylinders spark all the time.--------It is carburetion that kicks in above 1800 RPM or so.

Interesting. Learn something new every day. CDI's trouble shooting manual may be of use now. Thanks for the knowledge and help.

 

[paulywally]

Based on the fact that they are supposed to spark all the time and it was stated that they foul, it seems that your motor is not sparking and your carburetor is triggering properly. It sounds like coils or a power pack maybe.

I can't forsee 2 coils going bad at the exact same time. I think you're on to something with the power pack

 

[paulywally]

It was a Cdm or coil. If one goes it takes the other one on the trigger circuit with it, it doesn't ruin the coil it merely shorts it out I'm guessing? And causes two cylinders not too fire. Picking up a new Cdm tomorrow and will update.

Edit: I figured this out by following cdi electronics testing instructions and eventually swapping a Cdm from the top two cylinders to the bottom two. The bottom two stopped sparking and the top two started sparking so I found my bad Cdm. Cdi electronics recommends you replace all 4 of them but at 115 bucks a pop I told my friend to buy one new one and one used one off ebay to keep in the boat.

 

[paulywally]

New cdm fixed the problem. It was a bit tough figuring out which one it was but we tested all of them and one failed. Happy boating!