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1994 60hp mercury losing spark one cylinder at 3000 rpm

G

gbarger

New member
This weekend my motor began losing power around 3000 rpms. My troubleshooting so far.
I checked that fuel was in all 3 carb bowls, drained all 3 bowls(no water or junk) changed fuel filter.
I then removed one spark plug wire at a time and isolated that the missing cylinder was the top one.

Using an inductive timing light, it shows lost of spark at 3000 rpms on the top cylinder. I installed a new spark plug and no change in lost of spark. I then switched coils and again no change the top cylinder still loses spark at 3000 rpms.
I actually had a spare switch box, and changed switch boxes, with again no change in lost of spark in the top cylinder, what else should I consider. I have ordered a new spark plug wire, just in case it is shorting out at high rpm, but asking now for any other ideas as to what could be causing my ignition problem.

Thanks in advance,
Gary
 
The plug wires are the orginal and are 3 sizes 4 inch, 6 inch and 9 inch, of course it was the 9inch that was suspect so I could not just switch them around, I had to get a new wire.

I got the new plug wire today, and same thing spark failure at 3000 or so rpm, ordered a trigger coil from marineEngine.com. I will post follow-up when I get it installed.
 
Some of those engines have a rev limiter on them, disconnect it as i have seen them make a switchbox do goofy things. You should have the encased switchbox with butt connectors...
 
I do believe my problem will be the trigger coil. Once I got the old trigger coil out, I did measure the resistance as described by the online test procedure, and one wire (purple) was outside of the normal range that was listed on the test site, and that wire was the wire that sends the trigger signal for the cylinder that is not firing above 3000 rpm.

I do indeed have the encased switchbox with butt connectors, I do not know which wire would be the rev limiter control wire, do you happen to know/remember the color code for the rev limiter wire.

My box has 3 bundles of wires:

The top bundle is the 4 wires from the trigger coil.
The middle bundle is the 3 wires that go to the 3 ignition coils.
The bottom bundle has 5 wires. One red, which I assume is supply voltage, one black that is obvious ground.
2 black/yellow which is the kill circuit.
1 blue, which I do not have any idea what it is,(mostly the rev limiter)?



Thanks,
Gary
 
Received the trigger coil today, and got it installed.:D
problem fixed.
Thanks for the fast shipping and help in isolating my problem.:D
 
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