Can Ignition Coil be "bad" even if tests in "good" range?

[saladdin]

Took coils and module off to clean with thoughts of replacing coils because of age. They are original with 278K .Tested both and multimeter shows 8.2 and 8.4 for each. Am I good to go? Would you replace for the hell of it?

Is there a way to test the module?

[OldNuc]

Your coils are fine. The module will let you know when it has failed. They are not actually testable. There is a tester but it basically confirms failure diagnosis.

[saladdin]

Thanks again OldNuc.

[td1238]

If you want to measure them accurately, measure them at 70* room temperature. If then they measure over 8k, they are fine. Measurements under 8k indicate carbon trails and turn-to-turn shorting. However, resistance testing will not reveal internal arcing. Usually carbon trails and turn-to-turn shorts follow internal arcing, so if there is any present, resistance will lower soon.

Measuring them on a warm or hot engine increases resistance, and will give a false 'okay.' The coils can measure as high as 10k on a hot engine. Of course coils can also open up, and are more likely to do so on a hot engine, so if you wish you can perform both a hot and a cold test, one to check minimum resistance, and one to check for opens.

My original coils had internal shorting, and no indication was given by the engine (code-wise), except that there was misfiring and weak performance under load (it is more difficult to produce a spark when there is a high charge of fuel in the combustion chamber). However, they did measure about 7.6k ohms each at 70*F, and, upon replacement with new coils, performance improved greatly.

In my case secondary winding insulation was probably stressed because someone had installed Bosch Platinum Wire plugs on my car before I bought it. However, winding insulation can become stressed over time anyway, even with proper plugs installed and good plug maintenance performed.