While on a ride with a friend his softtail began running on only the rear cylinder. We pulled to the side and I checked the plugs, plug wires, and all connections. Found no spark coming out of one side of the coil. He mentioned that this happened a couple of times previously and thought it was the plugs. He would change the plugs out and it would be normal again. I said that a coil could present this problem when hot and in the time it took to change out the plugs (he doesn't carry spares so we're talking 90 minutes plus) it cooled down and thus the problem disappeared. On our discussion he went ahead and bought a coil and the problem still occurs. Now he wants to replace the ECM! He lives about 75 miles away so I've tried to help him remotely, problem is there is another who is leading him down the ECM route. Can anyone give some troubleshooting points that I can relay?