CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Intermittent spark plug fire

I have a 1977 Jeep J10 Pickup. After a while, it quits running - no fire. I can replace the ignition module or wait 20 minutes for it to cool and it will fire back up. I have replaced the ignition module, as well as the pick up and distributor - same things happen. What else could it be? Click and Clack said a few weeks ago that they replace something every time they replace the ignition module. Anyone know what that something is and if my Jeep has one?

The ignition coil might be the problem.

How old are the cap, rotor, wires, and plugs?

If there’s high resistance in these components, it can overdrive the ignition module causing it to overheat.

Tester

Have you verified that power is getting to the igntion system when the trouble occurs. If not, you should do that.

The cap and rotor are brand new. Wires and plugs, not sure - likely pretty old but there have been very few miles put onto this engine. I bought a re-built engine about 5 years ago - they more than likely used all of the old components (wires, plugs, etc). Not sure about the coil either - likely old as well. There is no fire going to the plugs when this happens. Used a spark plug lite wire to test. What Tester says makes sense - the overheating part. I can replace the ignition module with a “cold” one and fire is restored - until it heats again. So the resistance is what I think I need to get rid of.

I’d bet on the coil.

I’ll also vote for the coil. If you can check the resistance of the coil, check it cold and after the engine quits. You will probably see a huge difference.