79 460 I have a miss on the very back cylindar I think its number 4 passenger side very back. Any way I pulled the plug to take a look and see if there was something wrong and its not getting fire for some reason. I checked the cap and cleaned it but still nothing. I changed wires to see if something might be wrong there and still same issue, no spark. I took the plug out and hooked it up to the wire to see if I had spark but I couldnt see anything. Is there a special way to see the spark or does it need to touch metal? I switched plugs to see if it was the plug and its not because its working on the one I changed out. Could the problem be the dist cap? What else could the problem be sense its not the wire or the plug?

One other thing I thought was odd is when I pulled the back plug out it had like an extension on it. The plug threaded into an adapter that threaded into the block. Never seen anything like this. What could that be?

 

I believe that the threads on the plug have to be grounded. Or you need a new cap and rotor.

 

At sometime, someone stripped the threads in the block and it was drilled for a heli-coil or insert. Plug does have to be grounded to see spark and I too would be starting at distributor cap and see if spark is leaving there.

 

The interesting thing about it, it doesnt look like a heli-coil thread. I know what that looks like. The piece the spark plug screws into has a hex where you can put a wrench on it to loosen or tight it from the spark plug and at the end its completely surrounded the end of the spark plug except there is a small hole at the end for the spark. The spark end of the plug sets inside this thread plug like adapter. I guess it could have been used for a heli-coil but not sure just because of how its designed. It looks like it has been in there for a very long time.

 

Sounds like a mechanics trick to defeat an oily cylinder. The extension helps the plug from fouling due to oil getting into the cylinder.

 

Hellwilder, that could be what its for.