When has an ignition coil gone bad?

Discussion in 'Classic Mustang Specific Tech' started by guevara42, Dec 29, 2006.

  1. I just replaced plugs, wires, filter on my 66 coupe and it still sputters and sometimes stalls. I notice that it does it even worse as the car gets hotter. Any suggestions on what I should inspect next? I'm thinking coil????
  2. coils rarely go bad, but are often replaced. How is your timing? Rotor? Cap?
  3. bad coil???

    That's what I hear that they rarely go bad. I have a pertronix ignition so the timing is ok. I did check the timing today just to make sure and it was right on. The cap and rotor didn't look bad at all. Anything else you can think of?
  4. Timing?

    you checked the timing with a light? Where is it set at idle and 2,500-3,000 rpm?
  5. 2 failure modes of oil filled coils

    Oil filled cannister type coils will all eventually go bad. With continued use the oil cooks off, the coil overheats and the resistance goes too high to function properly. Typically the first symptom is that it will start and run when cold but shortly after getting up to temperature it dies. If you put your hand on the coil you'll find it's very hot.

    The second way I have seen an oil filled coil fail is if it's dropped hard. A sudden impact can lead to one of the two windings moving enough to make contact with the other (internal short), or break loose to create an open. The modern E coils don't have either of these susceptibilities, which is why the OEMs went to them in the mid 80s. Having said that, if your coil is relatively new (low mileage), and it hasn't been off the car since it last ran (not dropped), then it's probably not the coil.
  6. you can test the coil to see if it is the problem. get yourself a heat gun, and with the rest of the engine cold, heat the coil and then try starting the car. if it is hard to start, then likely the coil is breaking down. you need to heat the coil to where it would be during normal engine operation, iirc about 100 degrees roughly.
  7. Is it leaking oil from inside the tower? I've had two go bad and both were leaking the oil from the inside of the tower. Not sure if it was coming from the screw or not.
  8. no oil leak on coil.

    I sure don't. The coil is dry and it actually looks pretty good. I think the problem is somewhere else. Thanks for the pointer.:nice: