On the topic of coils, coil failure and things we can't test at home - here is a basic idea of what is happens when the secondary isolation fails on coil.
I tested the coils and they were fine.
Not to be mean; but other than visual and an OHM test (WHICH WILL
ALMOST ALWAYS PASS) if the engine runs at all, you can't tell jack from any test done at home and neither can 95% of the shops.
Its leakage voltage and arc-over voltage from the coils secondary output that we have NO WAY of testing.
((EDIT: I STAND CORRECTED, SEE VID BELOW. Hard to do on the Fiz, but possible when the chips are down. . .))
Here is a vid so you get the idea. In the ideal world, the sparks energy travels through an insulated conductor to the plugs gap where it jumps from the electrode to the ground strap. When coils fail, they often times leak high energy back to the input (primary side) and or jump to ground taking the path of least resistance. This is what most of us can't do at home is test the breakdown voltage of a coils isolation ability and/or the ability to delver the spark energy to the plug.
[ame=http://www.youtube.com/watch?v=dMBzwPAjvZ8]High voltage electric Arc discharge - ignition coil - YouTube[/ame]
In this vid there is no coil wire attached so the coil is at a disadvantage and the energy has no where to go but through the tower to the body & input source. If it was an actual acr-over/break-down test, it would have a wire attached and a specified gap which would be larger than that specified for the engine its used in. This is because during compression the combustion process increases the load on the ignition system. So a larger gap can simulate a bigger load like acceleration for example.
