HELP - Vanishing spark mystery

[aldridgehouse]

Hi - new to the forum - looks like a great place.

I have a problem that is totally stumping me - My wife's cj, 304 v8, had been running fine - last week she blew a heater hose - I went out, fixed it and drove it home - next time she drove it, ran fine for a while then started missing and stalling.

Since then I have figured this out - Runs fine, hits on all 8 cylinders til it gets good and warmed up - then it loses fire to the #2 cylinder - a few minutes later, it loses fire to the #1 cylinder and will hardly run. Let it cool down and it runs fine and has good spark to #1 & 2 again, til it gets warm.
Once it's warm, you could take #1 & #2 plugs and stick em in your mouth- they have no fire at all.

I have replace plugs, wires, cap and rotor, the carb before i realized it was spark related. I can't imagine anything else that would affect individual cylinders.

Anybody got any ideas or had similar problems before?
p.s. - sry for the long post.

 

[BakedAlaskan]

I would think if the spark isn't coming out of the distibutor then possibly the bushing might be worn out in the dist. But that sounds strange.

If the spark is making it through the wire and the plugs just fail to spark I would think A head gasket or cracked head. Since they are adjacent cylinders and only happens after it warms up and all.

 

[MudderChuck]

I had a similiar problem with 79, it turned out to be water below the mounting plate, in the distributor for the trigger (pick-up). When the motor got warm, the condensation from the moisture would cause a serious cross fire/miss fire.
Some of the early V-8 AMC motors had a condensor in the distributor, that when hot would fail, If you have a condensor, disconnect it.
When trouble shooting, miss fire, I´ve had good luck, with a timing light on the suspect cylinder, with the light pointed at a dark spot on the motor, you can see weak spark and miss fire easily.
A good quick test is to hold the spark plug cable near a ground and check the color of the spark, yellow splatter usually means weak spark, a sharp blue spark with an audiable crack usually means good spark.
Have had problems with dirty connectors, anti freeze, will short and gum up connectors, makes a coating of suger on the contacts. The best way to remove it, is with really hot water and mild soap. Most solvents don´t help remove it.
Have also, (but rarley) had problems with the coil, overheating, if it´s to hot to touch, you have a problem.
The ignition control model on the early V-8´s had a rep for failure, but I´ve never had one fail. There is an upgrade, using a MoPar ignition module, that is cheap and works well.
Just a few ideas.

 

[BakedAlaskan]

Hey aldridge, did you figure anything out yet??

 

[aldridgehouse]

Yeah - sry, i should've posted it long ago.

Not sure which one fixed it, but i replaced points, condensor and coil. Problem went away.