Detonation

Anyone else have problems with detonation? My 305 misses fairly often due to this. I talked to my mechanic and he said to check the back plugs, so I did and found that they were running too hot. I replaced one plug with a correctly gapped hotter plug and the car definatly runs better, but still misses sometimes. I guess I need to replace the other plugs now :( Anyone else have issues like this?

Anyone else have problems with detonation? My 305 misses fairly often due to this. I talked to my mechanic and he said to check the back plugs, so I did and found that they were running too hot. I replaced one plug with a correctly gapped hotter plug and the car definatly runs better, but still misses sometimes. I guess I need to replace the other plugs now :( Anyone else have issues like this?

If you're detonating due to the plugs, you need COLDER plugs, not hotter!

Run AC R44T or equiv. If these are hot, try an R43T.

There's lots of things that could cause this, the static ignition timing could be over advanced, there could be vacuum leaks, if it's carb'ed the carb might need rebuilt, there could be carbon in the combustion chamber (GM Top End Cleaner, Seafoam, Water etc). You could also have a plugged catalytic converter (especially consider this if the engine's running hot and power is down).

You should also make sure the EGR valve and system are operating properly. A functioning EGR can significantly reduce the incidence of detonation.