Hi, I'll take a stab at this. The most likely culprit that I can come up with if you've checked the normal stuff, (wires and connections, distributor cap and rotor) would be the ignitor. The ignitor is near the coil or in the distributor (carbuetor engines) Of course the ignition coil itself could be bad. I'll again say that I'm only taking a stab after going over the schematics that are in my Chiltons book. I certainly hope this helps and if anyone else has more, please add to this. Good luck. Steve H.