Went out in the car today and when my son and I stopped for lunch, he went to turn off the ignition and the car kept running. Looking a little befuddled, I told him to go in and get our lunch while I tried to figure out WTF just happened. I turned the key from off to run, back to off, etc a few times. The ignition key even came out of the cylinder from any position, which had never happened before. The car kept running. It never changed idle quality nor did it sputter. Eventually, I popped the hood and unplugged the distributor lead from the MSD unit to kill the car. He comes back out from the restaurant, we start the car, I tell him to shut it off and it shuts off OK, just like normal. Out of curiosity I check the ignition key to see if it will still pull out of the ignition from any position but it stays put, just like it should. Later, I'm driving with the wife and I downshift as I'm coming to a stop. I hear an unfamiliar popping from the exhaust. The car also seems to be idling oddly. Not a misfire but more like a lower idle than normal, then drive a bit, come to another stop, and it idles normal. It's hard to describe. Is it possible that the ignition switch is going bad and can be causing these little quirks, or am I going crazy? I've been driving the car hard the last few weeks in an effort to make sure it's got all the bugs worked out, and I thought I'd had everything nice and tight until today. Any thoughts?
In an MSD installation, the ignition switch just turns the box on. Since it doesn't take much current to keep the box on, what can happen is a small amount of voltage can back feed through the charging lamp indicator and keep the engine running. It is more common on older vehicles with external regulators. The fix is installing a diode in the regulator wiring to prevent the back feed. MSD boxes come with the diode and it is mentioned in the instructions.
Turns out, from what I can tell so far, that the secondary air door spring broke. Since I wasn't really getting on the throttle I never noticed the bog. Seems like the door was probably flapping, loading up the secondaries, and causing a rich condition that was probably flashing off in the unspent fuel. Proabaly responsible for the subtle changes in idle too, as well as the car smelling rich. I'll know tomorrow for sure when I take it for a drive. I took the carb off earlier and replaced the secondary air door spring, and put it back together. I also reset the secondary opening from 90 degrees to about 78deg, and replaced the secondary air baffle that I took out back in the '90s. Just playing with it a bit in the driveway seemed like she was back to normal if not a little better. Still haven't been able to replicate the run-on issue with the ignition though. I'll have to wait and watch for that to happen again. Time to get a a log book like I had in the old days.
