1983 258 #3 cylinder is missing at idle

[loyalpoke]

The #3 cylinder on my '83 CJ8 w/ AMC 258 i6 / 4.2l , all stock, is missing at idle: plug and wire is good, no vac loss or intake leak, compression is same as other cylinders at idle and increased RPMs, smog stuff has been removed, i've even been trying to use a positive thinking. Any ideas?

 

[Les]

The #3 cylinder on my '83 CJ8 w/ AMC 258 i6 / 4.2l , all stock, is missing at idle: plug and wire is good, no vac loss or intake leak, compression is same as other cylinders at idle and increased RPMs, smog stuff has been removed, i've even been trying to use a positive thinking. Any ideas?

Hmm....well, if you have verified your plug is good, the wire is good, you should make sure to check the contact inside the distributor cap. You might want to also swap the plug for another one to see if the miss moves to another cylinder, because sometimes the insulator can be cracked internally and it can cause it to arc and short out on the block. If everything seems to be in order, and your compression is good which rules out a leaky/burned valve, you might have weepy/blown head gasket.

I've had several over the years that developed a pin hole leak that sometimes wouldn't show itself unless the engine was cold, because once the engine heats up, the leak self-seals. If this is the case, the engine can run mostly normal and you won't see tons of coolant disappearing in the radiator. Id take a really good look at the color of your spark plug because it will be a slightly different color than the others, as well as closely check your oil for signs of moisture contamination.

 

[73CJ]

Try swapping a plug and wire.

See if it moves to another cylinder. If not, it could be the cap.

 

[mtnwhlr]