The wires are stock 1993 vintage. The current coil is an OEM Mopar replacement. All measurements were made wtih a Fluke 87 multimeter.
There is a 2 position connector that attaches to the coil primary winding. One wire is Green/Orange and the other is Grey. I am measuring directly across these 2 wires. I checked my method and determined that I was using a 100 mS sampling rate, which means that the max or min voltage would have to last for over 100 mS before the meter would record it. This gave me the readings ranging between 1.2 and 5.6 volts.
I changed my measurement procedure to a 1 mS sampling rate so that I would pick up spikes lasting more than 1 mS. This changed the results totally. Here is what I have now.
Measuring directly across the Green/Orange and Grey wires connected to the coil primary:
Idling: Min = 12 volts, Max = 147 volts
High RPM: Min = 12 volts. Max = 123 volts
Measuring between the Green/Orange wire and Ground:
Idling: Min = 12.8 volts, Max = 13.6 volts
High RPM: Min = 12.8 volts, Max = 14.0 volts
Measuring between the Grey wire and Ground:
Idling: Min = 1.2 volts, Max = 90.8 volts
High RPM: Min = 1.6 volts, Max = 69 volts
I am guessing that these high voltages, well above the battery / alternator voltage are generated by the decay of the magnetic field in the primary winding when the ASD shuts off the current to the coil. Since I can find no spec to compare them to, I don't know if they are normal or not.
So, what does this all mean with respect to my persistent ignition coil failure problem? At this point I have no idea, but I will continue to research it. There has to be something that is causing these failures and my opinion is that it is the new PCM that was installed immediately before the coil failures started to occur. The dealer simply keeps replacing the failed coils and claims that they must have been defective. I am skeptical that 3 defective coils have been installed in less than one month.
Any thoughts that anyone can offer will be appreciated.