Monitoring ignition on a 1990 Honda Si.

Very limited until more is known about the setup. Number one, what are you trying to learn?

Meanwhile, here are some sanity checks:

Is the shape of the waveform reasonable? Is the amplitude reasonable based on the probe attenuation?

Do the signals go away when disconnected from the 'scope? Do the signals go away when the probes are shorted to ground? Do the signals look the same when measured on a single plug?

Does measured amplitude decrease smoothly as the clamps are opened on the wires?

If all the answers are yes, then your interpretation is reasonable. It might even be correct 8-)

If you have the option of using a pulse transformer to measure the spark current that might be easier to deal with. Less noise, better calibration stability. Voltage and current measured simultaneously are the most persuasive measurement.

hth,

bob prohaska

My knowledge of ignition systems is minimal. My intention is to have some diagnostic information available when the the vehicle is on the road and the motor malfunctions.

Was hoping someone with automotive knowledge would divulge.

Was hoping someone would divulge.

The engine was running when I caught the picture. No obvious malfunction.

Can check in the coming weekend. Thanks.

First I've heard of a pulse transformer. Will read about it when there's an opportunity.

Thanks for the questions and tips, ... P.

I'd suggest digging around on the Net to find explanations of how ignition systems work. Good keywords might be CDI, Kettering, breaker points, breakerless, transistorized ignition in your choice of permutation. The page at

As a guess, I'd suggest it'll be a fast rise to 10-40 kV, maybe a few microseconds at peak and a rapid collapse to a few hundred volts or less. It may ring, perhaps 500 kHz, and be over in a millisecond or less. The pulse is likely to be negative, but not guaranteed.

Agreed, the waveforms look reasonable to a casual glance.

If you're new to oscilloscope use I'd suggest making a practice rig using an old coil, capacitor, switch and sparkplug. That'll be much easier to learn with. Lots of things can go wrong with pulse measurements, much simpler on the bench than on the engine.

hth,

bob prohaska