I just put my 4th ignition coil in this 1993 Jeep Grand Cherokee in the last 4 years. I have driven minimal miles during this period because I have lost confidence in the vehicle. My mechanic says very little mechanically can cause an ignition coil to fail and blames it on bad parts from the supplier. Does this sound reasonable or can something else he’s not aware of be causing this?
I’m presuming on a 93 you have the single coil configuration with a conventional distributor, not the coil on plug design. Too wide of spark plug gap can damage a coil. Or if the spark is shorting out before it reaches the spark plug tip, or in parallel with the spark plug. Beyond that, the coils have to be properly installed so the heat-sink method is doing its job. They’ll get hot and burn out if not mounted to the heat sink like the manufacturer intended. If I had this problem on my Corolla and I didn’t want to pay a visit to the local shop for a proper o’scope diagnostic, which is the best method, I’d ohm out the spark plug wires from the distributor cap all the way out to the plugs for shorts. And from the coil to the cap if that’s possible to do. And I’d look inside the dist cap for signs of arcing, carbon tracks. I’d also idle the engine is complete dark, look for signs of flashing in the engine compartment. If nothing found, I’d replace the dist cap, ign rotor, plug wires, and spark plugs, making sure the gap is correct. Still happening? Replace the ignition module or igniter. The circuitry in those modules that powers the coil full force during cranking, then limits the current when the engine is running may be faulty.
It’s possible you are just unlucky and getting bad parts too of course.
My mechanic did mention the spark plug gap possibility. I will discuss some of your other suggestions with him. Thanks.
I have not had any problems with factory coils on these, failure is rare. I had one magnum engine towed in with an aftermarket coil and no spark. After close examination I found that the connector pins in the aftermarket coil were smaller in diameter than the factory coil. This resulted in a loose and intermittent connection. That was an unusual problem.
It would help to know the the nature of your coil failures but some mechanics just replace parts saying they are “bad”. Even if you are using quality coils there could be a connection problem due to spread or weak connectors. The next time it won’t start apply pressure to the coil wiring connector while trying to start the engine.
During the last few months that I owned my 2003 Mustang GT, I had no fewer than four coils (COP ignition) fail in three months. One each failed within about 2-3 weeks after the other. It was a bit uncanny, but I guess it makes sense seeing how they were all the same age.
I recall a service bulletin that required modifying the distributor base on some Jeep 4.0L engines to bring the rotor/plug pin in line. The air gap at idle was extreme causing secondary voltage to spike.
The TSB regarding modifying the distributor seems to be on older models but I found several sources mentioning issues with excess air gaps from the rotor to the cap and crank angle sensors that threw stray triggering impulses, both those situations cause secondary voltage spikes which can burn out ignition coils.
I’m not really surprised. The coils are manufactured very consistently, and thus have very consistent lifespans. It’s not at all unusual when one goes to have the others begin dropping out too.