The Good, The Bad, And The ????

[Joe C.]

Let's talk about coils..... ignition coils. Do they slowly "go bad" (weaken with age)? Are they either "good" or "bad"?? Is a blue spark or yellow spark OK??? This is, of course, with a strong battery, and correct (and new) ballast resistor).

Seems to me that the pri/sec windings are insulated, and cooled with oil. So, barring any opens/shorts to ground, the coil oughtta work within its design parameters. THE QUESTION IS.......IF THE ENGINE STARTS AND RUNS, CAN THE COIL STILL BE MARGINAL, OR WEAK??

[Duke W.]

Re: The Good, The Bad, And The ????

Old coils can get flaky with age when they get hot as they do on an operatiing engine. The best way to verify the operation of your coil is probably to borrow of buy a inexpensive replacement and try it out. If the problems disappear, there's a good chance the original coil is getting tired. If not, you know to look elsewhere.

Duke

[Wayne K.]

Re: The Good, The Bad, And The ????

Joe,

Yes, if the engine starts and runs the coil can still be bad. My only experience with a bad coil was on a car that ran fine until it was put under heavy load like trying to accelerate up a hill and then the car would buck like the ignition was being turned off and on. I figured it was the coil as the day before I had accidently hit it when I slipped with a wrench while tightening something else. The jar caused the coil to go bad.