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15HP Merc No Spark on Bottom Cyl

D

dav505

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"I have a 1989 0C128638 that s

"I have a 1989 0C128638 that seems to have no spark on the bottom cylinder after the motor has ran and then stopped. Upon restart, there is no spark on the bottom cylinder. When I try to troubleshoot in a barrel in my garage it always works fine, probably because it's cold. I am ready to start changing parts but which ones?"
 
"Start by swapping around the

"Start by swapping around the two coils - if the problem moves, you know it's the coil.

The ignition system on that particular model is very durable with the coil being the weakest component, so that's the place to start..."
 
"Graham, Thanks for your reply

"Graham, Thanks for your reply. Not to sound to stupid here but the spark plug wires are potted into the coil output with somekind of thick tar or glue. The wires are custom length so I will need to swap the wires too. How do I separate the wires from the coil? Thanks"
 
"That goop is most likely a bi

"That goop is most likely a bit of grease that was either put there to help keep any water and other cooties out, or has simply collected over time.

The wires come out of the coil similar to the plug end of things - simply twist gently and pull - they don't "click" in the way the do on the sparkplug, but the connector is similar.

When you move the coils, make sure you swap out the little wire that feeds them as well.

The long screw that goes kinda through the middle of the coil is what keeps it in place and acts as the ground (the tab on it is connected to one of the tower pins on the coil).

The wire that goes to the little tower post (green/yellow on one coil, green/white on the other) is what you need to move when you swap the coils to keep them firing in the correct order.

And yes, simply swap the plug wires and then give her a try."
 
"OK, I swaped the coils last n

"OK, I swaped the coils last night and I still have the same result: No Spark on th Bottom Cylinder. What should I try next?"
 
"Dave, rather than try to post

"Dave, rather than try to post a variety of tests, I have fired you an email (hope your email address is good).

It's a pdf file of the whole ignition system including tests/proceedures..."
 
Looks like a new switchbox did

Looks like a new switchbox did the job. The motor purrs like a kitten!
Thanks for the help from all.
 
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