cliffyk

This may be common knowledge, however I have not seen it commonly mentioned on any of the forums--that may be because it has no real impact on anything, I found it interesting nonetheless...

In playing around with a new set of isolated ground, insulation piercing, probes that came in last week I recorded the #5 cylinder's primary waveform across the COP this morning and found this:



I had to check my connections and 'scope setting 5 times to be certain, but sure enough the plug fires three times in succession at engine speeds below 1200 rpm!

There is no mention of this that I could find in the shop manual, although I did find some general info on the web. It is an emissions related behaviour, intended to reduce hydrocarbons at idle.

Thought it might be of interest to some of you...

35thAnni99GT

Damn CARB making my mod motor COPS fire 3 times, lol.

myslow2002gt

Yep, that's what it's intended for. There are aftermarket ignition adds on, like the plasma booster that are used to keep the plug firing multiple times all the way up the RPM band.