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2005 Mercury 90 2 stroke firing issues

C

classicgen

Member
I have a 2005 90hp 2 stroke that I am having issues with. Started out surging at higher rpms...seems to run smooth at lower rpms. Installed new plugs, no help, got a new CDM module and did the typical swapping out of the 3 and no difference...Not sure what to look at next. I ran it yesterday on the water and pulled the cover off. Top two rubber boots on the spark plug covers were very hot to the touch...bottom plug was not hot at all. I also pulled the plug wires off while running...top two throw a spark a long way, bottom plug only tries to spark when the boot is almost completely on. No long throwing of a spark like the top two. Also I have 2 yellow wires coming off of the regulator that looked to be burned or have gotten hot where the clear connectors are. Should I be worried about this? Thanks for any help.
Ken
 
.." Also I have 2 yellow wires coming off of the regulator that looked to be burned or have gotten hot where the clear connectors are.

That's just the charging circuit--the ignition system makes its own juice. I suspect a bad coil--seen a lot of then lately. Try swapping two of them and see if the problem moves with it.

Jeff
 
Jeff,
Thanks for the info... I installed a new CDM module / coil on the bottom, no difference, swapped them out all the way up and it made no difference.
 
A CDM module is just a minature switchbox, get a spark checker so you can test spark as it need to jump a min. 1/4" spark and yes the rectifier can cause spark problems. Below is testing


No fire or Intermittent on One or More Cylinders:
1. If the cylinders are only acting up above an idle, connect an inductive Tachometer to all cylinders and try to isolate the problem cylinders.
2. Using a set of piercing probes, check the trigger DVA output as given below:
Wire Color Check to Wire Color Resistance DVA Reading
Purple wire Engine GND Open 1V or more
White wire Engine GND Open 1V or more
Brown wire Engine GND Open 1V or more
NOTE: These triggers have the bias circuitry built into them, therefore you cannot measure the resistance like you could the older engines. In addition,
there are four triggering coils used.
3. If # 1 is not firing, disconnect #2 CDM module and see if the #1 module starts firing. If it does, the module you just unplugged is bad. If it does not,
disconnect #3 CDM module and see if the #1 module starts firing. If it does, the module you just unplugged is bad.
4. If # 2 or #3 are not firing, swap locations with #1 and see if the problem moves. If it does, the module is bad. A continued no fire on the same
cylinder indicates a bad trigger.

1. Disconnect the black/yellow kill wires from the harness and retest. If the engine’s ignition fires now, the kill circuit has a fault-possibly the key
switch, harness or shift switch.
2. Disconnect one CDM module at a time and see if the other modules start firing. If they do, the module you just unplugged is bad.
3. Disconnect the yellow wires from the stator to the rectifier and retest. If the engine fires, replace the rectifier.
 
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