Ignition Coil Overheating

Ignition coil failures are rare but they can happen. Can coils have a slug with two windings made with enamel coated copper wire. A turn to turn short is a disaster, significantly loading the coil resulting, in a weak spark. The short may be intermittent, related to internal expansion and degraded insulation. Checking coil resistance is not helpful, because one shorted turn out of 100+ is in the mud.

As Del suggests testing can be difficult. It involves testing hot, looking with scope, or inductance measuring equipment. With a spark tester it may be necessary to close the gap to see a faint orange spark.