Re: AC or DC

[vintin]

I believe the second scope photo shows the resonant frequency (ringing) of the inductor/capacitor. A leaky capacitor is going to shunt and reduce the amplitude of the voltage spike and resonant voltage. It is my understanding that this ringing results in a longer spark plug arcing duration. A capacitor that has changed in value would result in a change in frequency of the ringing. By collection some data from known good coils and capacitors (resonant frequency and voltage amplitude) it should be fairly easy to figure if a capacitor is out of spec.