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POLAR_JEEP_04
May 3rd, 2012, 07:20
A friend of mine has a 93 with a 4.0 and he came to me with an issue that I can't figure out. Now im not much of an electrical guy so this might be a easy one and I'm just not getting it but anyways here it is. The jeep will run and drive fine for a few month or weeks then randomly blow the coil. He has had the jeep for awhile now and has been through a pile of new coils. I have never heard of this before so I figured I would ask here before ripping into the harness.

Jcool83
May 3rd, 2012, 22:16
I have not had this problem with my XJ
i did have the original coil fail and would shut down all power once it got too hot.

and is he replacing it with NEW coils or reman ones??

8Mud
May 3rd, 2012, 22:36
Never had that problem on an XJ. Some causes may be the alternator is overcharging.
I doubt the problem is in the harness. The power to the coil is the same power to the alternator and basically just battery voltage.
I have seen systems with excessive resistance cause the high voltage spark to take strange paths and actually burn a hole through the top of the coil near the coil to distributor cap wire.
If he is replacing the coils with after market and not XJ specific, you may need a ballast resistor to keep them from burning up.

Rags
May 3rd, 2012, 22:55
I would check actual voltage at the coil with the jeep running, take readings with the rpm increased, anything above 14.99 is excessive, if voltage is good, make sure the metal bracket is clean that the coil bolts to, also are the replacement coils fully encased in a plastic shell? or can you see metal around the perimeter of the coil assembly? Might be just the quality of the coil or some weird thing going on the coil is being powered up when the vehicle is sitting off..... any other problems? Popping light bulbs? dead battery? Alarm plumbed into the ignition feed circuit in any way?

Is the coil wire fresh along with all the other secondary igntion stuff like cap.wires etc?

Poke around the harness to the coil, does it look okay? not pinched, rubbed threw?

I hope you find the prob :):thumbup: