Testing coils on a coil over plug system?

[art leong]

Originally Posted by buzzinhalfdozen

Art, if you have 12.5 volts at battery and 11.8 volts at coil you are seeing voltage drop in that circuit, what voltage does the coil have when it's running?

The only thing on is the O2 sensor and the ECU. I'll check it with the O2 sensor unplugged
When the car starts and runs the voltage goes to 13.9