I've had a few heat-related problems with my 1979 400. First was an ignition module that spontaneously went bad one summer day. After that, everything seemed to run fine for a while, until I got to the end of the season and I had it stall out on me again when it heated up. I replaced the ignition box again, no joy. I replaced the distributor pickup, still no joy. At this point, I decided that instead of throwing good money after bad, I needed to figure out what the problem was before buying any new parts - you know, actually diagnosing the problem. The main suspect at this point, of course, was the ignition coil; it had survived the engine fire, it was the most likely culprit due to that and due to the symptoms (idled fine at any temperature; once hot, stepping on the gas even slightly would stumble and stall out). But how to test it without sitting on the side of the road, fighting with my DVOM test leads, and waiting for the tow truck to bring her back to the garage? That's when I hit on it. I took the coil out, heated my oven to 200 degrees, put the coil on a baking tray and baked it for 20 minutes. I put the test leads on it, and voila, I discovered that the elevated temperatures drove the primary resistance well out of spec - at 200 degrees, it recorded 2.3 ohms, where the spec for Duraspark II systems is 1.1-1.3 ohms. Problem solved, and I found a new way to test heat-related failures in my engine, to boot. I just wanted to share in case it helps other guys test heat-sensitive ignition components without having to drive on a poorly running engine.

 

That's thinkin' outside the box!

 

Thinking outside the hood. Good idea!