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2002 Mercury 90HP fires intermittently

M

makinard

New member
I have a 90 horse Mercury that fires on the top cylinder whenever it wants. Checked coil packs and they are good. Any help would be greatly appreciated.
 
I suggest switching coil packs and see if the problem moves to that cylinder.

Switch everything you can to make it a viable test.

Jeff
 
Symptom of a bad CDM module, download the CDI troubleshooting manual and test. A module that working can be bad and effect a good one making it look bad
 
When I switched coil packs problem did not happen. They all 3 were firing. Moved everything back to original and problem was still gone. Checked it 5 minutes later and top cylinder isn't firing again. It is a 2 stroke. I did notice the wire connectors were a little burnt looking. Could just a connection issue be my problem?
 
Hmm....... you've swapped the cdms around so we know they're all ok. Have you swapped plug wires around as well? Intermittent problems like this always set my spidey-senses tingling towards a wiring problem. Also check the trigger wires for any sign of wear or breakage.
 
Moved everything back to original and problem was still gone. Checked it 5 minutes later and top cylinder isn't firing again.
Click to expand...
You got a bad CDM module......now you need to figure out which one.
http://www.cdielectronics.com/downloads/troubleshooting%20guide/Mercury-Force%203%20Cylinder%20CDM.pdf
 
Yes I swapped plug wires around as well and it sat there and ran great, firing on all cylinders. I'm new to these motors but to me it sounds like a wiring issue as well. Thanks for your help.
 
Even if it works fine for awhile and then stops working the CDM module could be bad? I'm guessing that these modules slowly go bad instead of just completely dying? Thanks for your help!
 
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