1998 Cherokee. 4.0 inline 6. Single coil.

I have had 2 ignition coils go bad in less than 2 years. I have the bad coil in the jeep and have not inspected it yet.

I talked to the tow truck driver who said this is a problem with this particular build. I suspect this is a heat issue based on where the coil is mounted.

Thoughts or solutions are greatly appreciated.

Grab today and make it great.

 

If you are using aftermarket coils....don't. They, for the most part, are all junk. Marginal insulation that isn't designed to hold up to the vibration of engine mounting. OEM part is the only way to go here.
If you are using an OEM coil, have you changed the cap, rotor and wires recently? Firing an unloaded coil will kill it quickly.

 

Radi,

Thank you for your response.

Although I can't without a call verify that my old shop used OEM coils I do know after 15 years with them they have a standard of using OEM parts unless requested otherwise by the customer.

The cap, rotor and plugs were changed in Nov 2011. The wires appear to be in good shape from a visual inspection. I know that does not mean everything but I have no issues with rough idle so it appears all cylinders are firing correctly.

Based on your response and my initial analysis both make sense as heating up and cooling any metal time and again will make it brittle and then overtime the vibration will cause it to crack.

I was hoping to determine if this was a chronic problem to determine if it was worth designing a heat sink to go between the block and the coil.

I still need to visually inspect the bad coil and if I can find my multimeter (recently moved back to Wyoming) test the copper winding to see if there is an open.

Current is also the enemy, hence your reference to firing an unloaded coil, again excessive heat is generated and can destroy the connections at the coil ends. A short or reducing the resistance of the circuit will increase current flow I=E/R.

Ok a little troubleshooting is yet in order. You have my brain spinning.

 

I don't think it's a heat issue. There have been thousnds of XJ's built with the coil mounted in the same place, so "Paticular Build" is BS. A heat sink would be a waste of time in my opinion.

The OEM coil in my '99 failed after 11 years and 129,000 miles. I was seeing a stumbling problem under heavy acceleration. I replaced the coil with an Echlin coil from NAPA and its been doing well for the last 8,000 miles.

What symptoms are you seeing that you had to change the coil twice in two years?

What brand coil did you use as a replacement each time?

The OEM coil cost around $59.00 and the Echlin $44.00, Delphi coil $49.00.

 

I'm suspicious of the wires. Back in the day at the dealership, we replaced plugs, wires, cap and rotor every 30,000 miles. IIRC the interval for the wires was 60,000 miles, while the other parts were 30,000 miles.

But, we found that the wires would often fail before the 60,000 interval so we just shortened up the interval to 30,000 with the rest of the parts. No real additional labor involved and customers were happy.

The wires having alot of resistance is not gonna give a bad idle necessarily unless they're real bad. When they'll fail is under load.

 

ccken,

Good morning, thank you for your response.

As to the end symptoms the jeep died both times and would not start. The coil had a total failure.

 

cruiser54,

Thank you very much sir. With the first coil there could be a stutter under load. LOL!! With the second coil it just died.

I have about 20k miles since the last tuneup. I guess I will be changing the wires and while I am at it might as well do new plugs, cap and rotor.

Thank you again.

 

It's the crap that we call gasoline today that's killing your coils. Today's gas is a lot harder at ignite than the gas that was available when your Jeep was first sold. The resistance in the wires, gas that is harder to ignite, a spark plug gap that is too big for that crappy gas, all put a lot of stress on the coil. The coil is almost at its kv capacity just at idle with the fuel we're forced to run today. Closing the spark plug gap by a few thousands will help a little. The reason everybody is going coil on plug is because it offers less resistance to ignited the gas with 10% ethanol we have today. The suits that make the laws we live by want to increase the ethanol to 15% , then 20%. All in the name of being "green" , it gives them warm and fuzzy feelings as they steal from us hard working types.

 

^While I've learned to silently suffer the fact that the greedy capitalists and overzealous bureaucrats are in bed together, the bit about the gas is spot on.

You should see what it'll do to a lawnmower's fuel system, too...