Can a coil be bad part-time

Possibly can be temperature affected.

 

Its possible but the problem is more likely to be a faulty HT lead or bad contact on the LT blade connectors.

But internal insulation breakdown can happen which results in arcing which might be worse in colder damp conditions.

 

Yes, but I'd put a higher probability on a power module misbehaving in that way (but you can swap coils and/or power modules to determine if the problem follows any of the 4 players).

 

Temp and humidity can both make a coil intermittent.

 

Yes they can! Had that happen years ago on a 1971 Boss 351 Mustang. Had several symptons, like carb or fuel issues, felt like perhaps timing even. Changed out several parts, still had the intermittent runability problem, changed the coil, no more trouble.

 

Me too - I've had intermittent problems with a coil - usually with it breaking down as it gets hot.

 

All of the above

 

+1

 

I had an intermittent skip on my Mustang GT over the past month. I spent $150 on Ford racing wires and platinum plugs. No change. I swapped out one of the coil packs with a spare I had in the garage. Skip went away.

 

I had an intermittent coil on an old 1973 Kawasaki F11 a while back. It would run great for a few miles and then start sputtering like it was running out of gas. After stopping for 10-15 minutes, it would run great again. Turned out to be a bad coil that after getting hot, the resistance would increase resulting in low voltage which caused the sputtering.

 

I totally agree. FYI, use some contact cleaner on the connector to the coil module and see if the problem goes away. Just happened to me this morning and now after lubricating/cleaning it, I'm back on full power. If that doesn't do it David, replace the coil module only. Should take care of it. Probably don't need to replace the coil itself just yet.