Mis Fire

[KayceeZ]

I have a 1973 240Z and the #2 cylinder is not firing. I have checked the spark plug and the spark plug wire and they seem to be okay. I am concerned that I may not be getting enough spark. What should I try next?

Thanks, KayceeZ

[Arne]

Have checked the compression yet? That would be my next move.

[SteveJ]

Did you check the distributor and cap, too? Do you have a spark going to the cylinder?

[KayceeZ]

I finally got time to check the compression and cylinder #2 has very little to no compression. This does not sound very good. The remaining cylinders compression was good.

Thanks, Kayceez

[Arne]

Has the car been sitting for some years prior to your firing it up?

[KayceeZ]

Arne,

No, the car has not been sitting for years. I have own the car for a couple of years and drove it a few times each month. About 3 months ago, the car was mis-firing in the same #2 cylinder. I replaced the spark plug and it seemed to solve the problem. Now, a change in the plug makes no difference. I'm getting a charge thru the plug wire, but the #2 cylinder is not firing and I have no compression is this cylinder. Any help is greatly appreciated.

KayceeZ

[Arne]

Not good news, then. It sounds likely that you have a valve problem. Perhaps burned, perhaps stuck partway open. The other possibility is broken rings, but in that case you often get a little compression, not zero. I suspect a valve problem.

First check the valve clearance on that cylinder. If that seems normal, turn the engine over and see it the valves are both moving smoothly. Last, turn the engine until both valves for that cylinder are closed, and apply a little (just a little) compressed air through the spark plug hole and listen for leaks. You should be able to identify intake, exhaust or crankcase that way.