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Spark Jumping From Center Lug On Coil

K

KCTractors

Member
Location
Central Wi
This is on a Moline 602 Gas with a Pertronix Ignition system 12 volt, the spark jumps from the center lug of the coil to one or the other terminals on the coil and makes the engine miss. I cleaned the top of the coil off and will be good for awhile. Get a little snow on the coil and it will do it again. Any ideas what would be causing this.
 
Bad wires rotor or cap. (or all of the above) A bad wire is most likely. Use magnetic suppression wires, or pure copper wires. The wires must have near to no resistance. The cap and rotor need to be correct for each other and the application. If wrong, they can also ad to the total secondary resistance. A wide open spark plug is also additive. Jim
 
Coil top is cracked or "carbon tracked" or there's an issue with the coil wire, cap and rotor, or one or more individual spark plug wires causing a extremely high resistance condition in the secondary circuit causing the high voltage to build up and seek a ground, other than through the gap on the appropriate sparkplug.

If the carbon center terminal in the cap is burned away or missing, or there's too much gap between the tip of the rotor and the appropriate secondary terminal when the coil "fires" that will cause what you are seeing.

Several times I have seen a mis-match between a Pertronix unit and the distributor it's installed in cause the spark to occur when the rotor is in between high tension terminals.

To diagnose this, I run the distributor n my distributor machine with a spare cap with a hole cut in it so I can see where the rotor is in relation to the high tension terminals as the spark is occurring. I hope I've explained this so it makes sense to your.
 
Put on a new cap, and make sure your wires are seated in the cap before rolling the boots down on the terminals.
 
Dielectric breakdown is the tech term for insulation becoming a conductor.

The rotor on my new and old GMC truck does it. Takes about 2 years.

Time for a new coil.
 
When you start using high voltage capable high energy after market ignition systems especially if running wider plug gaps resulting in higher firing voltages, if the coil top and its HV tower and the cap and rotor and plug wires aren't all in good shape with no hairline cracks or carbon traces or faults THOSE PROBLEMS CAN REAR THEIR UGLY HEADS. Id be checking the coils top HV tower for carbon traces or cracks and the coil and plug wires for a break or open that allows the voltage to rise too high so it jumps where you mentioned. Try a new set of coil and plug wires if the coil is okay !!!

John T
 
In addition to all the other good info. Do you have rubber boots on your coil wire to keep moisture out ? Are the wires any good ? I have seen where a person installed new wires and did not have the ends crimped on as to make proper connection. So then the spark could not get through.
 
The cause is a build up of ions on top of the coil. Wiping off this tracking may be effective until they build up again and form a new unwanted path. That's my theory if there is no crack.
 
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