[Boxstard]

Originally Posted by blue62

Start with a visual inspection.
I always use a flashlight.
If they have any type of physical damage like cracks in the housing (even hairline cracks) I replace them.

A simple test you can do on a coil yourself is an Ohm's resistance test.
If a coil doesn't meet manufactures spec. it should be replaced.
You can usually find the manufactures spec on the internet.
All you need for the test is a Digital multi meter.
If you do your own auto work you should have a Digital multi meter in your tool box.

Yeah that’s pretty basic…. For me cracking can be repaired and may not warrant automatic replacement, if you catch it early. Body crack can be filled with epoxy, and tube can be insulated with electric tape. One of mine had tube split and taping it up works fine.

I do have a multimeter, but just wondering how to tell actual degradation, instead of just continuity of the coil. Variation in reading within the spec. may come from manufacturing tolerance, instead of aging. If the coils with resistance within the spec. can still produce weak spark, then the check is not effective and I wonder what else can be checked.