Mechanics

IGNITION COIL

1994 Jeep Grand Cherokee • V8 4WD Automatic • 10,000 miles

Is there anything that can make an ignition coil fail?
Avatar
Hook Turner
April 18, 2011.



Too much heat, quick temp changes, physical impact.

Wrenchtech
Apr 18, 2011.
Change the plugs and plug wires, distributor cap and rotor. Check voltage and ground circuits for the coil. Coil wire.

Your computer switches negative side of coil to induce secondary voltage. Any trouble codes?

JDL
Apr 18, 2011.
No trouble codes, but this is the 3rd time in just a few weeks that one went bad on me. The last one only lasted about 10 miles.

Tiny
Hook Turner
Apr 18, 2011.
I doubt the coils are even the real problem. A new one just increases the KV a little.

Wrenchtech
Apr 18, 2011.
Well the original problem is the engines dies. No spark to the plugs. After replacing the coil, the engine runs. The first time was a few months ago, then a few weeks ago and the last time was about 2 days ago. But each time is the same, engine dies (no spark).

Tiny
Hook Turner
Apr 18, 2011.
So I guess I am wondering if something is ruining the coils or am I just an unlucky purchaser of bad coils?

Tiny
Hook Turner
Apr 18, 2011.
You might try buying an OEM brand instead of the discount brands.

Wrenchtech
Apr 18, 2011.
I think you're right about that Wrenchtech. I wasnt sure the coil was my problem at first, so I bougth the cheapest one to try, but since it has a 1 year warrenty, I've been getting them for free since. But before I spent the extra cash, I wanted to be sure I wasn't doing something wrong or maybe had another problem to look at first. Thanks for the advice you guys!

Tiny
Hook Turner
Apr 18, 2011.
Excuse me for jumping in here. I read through everything very quickly and from what I see, the engine stalled, you replaced the coil, the engine runs for a few weeks, then it stalls again, is that right? How about if I reword it like this: the engine stalls, you let it cool down while you tried some stuff, then it ran again after it cooled down. I think you're assuming it was a bad coil because the engine ran after you replaced it, but what if the engine also ran after you replaced the wiper motor or brake light switch? What my meaning is, is the coil might not be bad.

The next time it stalls, if you have no spark, check for voltage on the 12 volt feed wire to the coil. On the cars that is the dark green / orange wire. Not sure of the color on the Jeeps, but you should find 12 volts on both of them for one second after turning on the ignition switch, then again during cranking. If that voltage is never there, there is a break in the circuit back to the automatic shutdown (ASD) relay, or the relay itself is bad, but that is very uncommon. It's more common to have 12 volts for that first one second but not again during cranking. That would indicate a failure of the crankshaft position sensor or the camshaft position sensor. Both often fail by becoming heat-sensitive, and they will work again after they cool down. When they fail, the Engine Computer won't turn on the ASD relay and the fuel pump relay, if you have a separate one, so you won't have spark or fuel pressure.

If this turns out to be the case, I just wanted to save you the frustration of looking for the coil problem. Another clue would be if any of the previous coils works when you stick it back in.

Caradiodoc
Apr 18, 2011.