clare at snyder.on.ca wrote

A minor missfire can also cause the converter to overheat. Imagine
what happens if the engine "diesels" on shut-down.

We salvaged the car and got a few more years out of it, but if IT had
been on dry grass on a breezy day, that would have been the end of it.

Yep. I had an Olds that was suddenly having intermittent loss of almost all
power, then it would be fine. I was driving it one day and hit a bump, and
heard a strange "ker-thump" (that's technical car talk g) then it lost all
power.

Long to short, I started thinking about the 'ole potato in the tailpipe, and
how it behaved like that. I cut into the pipe downstream of the converter,
and saw that all of the pellets had melted into a perfectly molded lump,
just the shape of the back part of the cat. shell. When I hit the bump, the
lump rolled into the outlet, and shut off the exhaust gas flow. Really
lucky to trouble shoot that one!

It is hard to say how hot it had gotten to melt the pellets, like that.
Certainly hot enough to start a fire.
--
Jim in NC