Mopar Electronic Pickup Polarity and Rotor Phase

BillGrissom said

Don't apologize. Good to add to an existing thread about a general issue which interests everyone. Renewing it keeps it alive. After a time, the photos become archive-only.

Re your question, with reversed polarity, most ignition modules will still trigger and you can adjust the distributor so the timing is "about right", but it won't be ideal because the trigger point will jump around so won't get consistent spark timing. That is because when reversed there is not as sharp a leading edge on the rising part of the signal. I just scrolled up to post #1 by Kit. Didn't you see that clearly explained in his O-scope plots?

Click to expand...

I did read that in the first post but I got to (over)thinking and confused myself with all of the factors involved. I like to think I have a degree of intuition when it comes to mechanical systems but with electrical... not so much lol.

The main reason I ask is I have a Pertronix Digital HP box in my '72 D200 and a Summit Billet distributor which uses this style of trigger system, same as a Mopar electronic distributor. For a long time I've been chasing an erratic idle and odd running issues that I finally narrowed down to being ignition-related. Yesterday I had the cap off the distributor and noticed what looked like a phasing issue (original thread HERE) where it looked like the rotor was way out of phase with the contacts in the cap. I thought about it some more and remembered that the ignition box can be set to either rising edge or falling edge (it had been set to falling). I changed it to rising edge and re-set the distributor (had to advance it a ton of course) and it seemed to run better. Thing is, in the instructions for the ignition box it says to use falling edge for magnetic-pickup distributors. In my mind I was over-simplifying the signal from the pickup though; I thought it was a simple sine wave when in fact there's more to it.

Today I was doing a bunch of research to figure out what the heck was going on and stumbled upon this thread along with one on Moparts where someone was having a similar issue. It led me to the conclusion that I must have wired the pickup reversed to how it's supposed to be. I was hoping that since I switched the ignition box to rising edge it would trigger at the correct point on the voltage curve with the wires being reversed. However @BillGrissom you are saying that's not the case? I guess I was hoping I wouldn't have to go and swap the wires back because it likely means I need to also reposition the reluctor wheel on the distributor rotor. I did find it strange that I had to do that back when I first installed the distributor because it misfired like crazy and I ASSumed the reluctor had been installed wrong from the factory.