Wiped cam lobe or lobes? I ran an 8ga. ground wire straight to the pass. side head then 8ga. from the driver side head to the frame, then a 10ga. Wire from each head to the fire wall. I also grounded the HEI dist. at the base. I thought when coils went bad they just died. This sort of sounds like a dist. wire grounding, you said that it runs great then switches to bad, sounds like a bad connection or a loose wire flopping around some where with a bear spot on it an is grounding. I'm just guessing. I had an old points system an the black wire from the coil to the dist. had a bear spot on it an at speed it would cut out then run then cut out again, took forever to figure out. You might also look at the connectors inside the spark plug boots on both ends.
Last edited by dogwater; 09-19-2013 at 08:38 AM.