Karl,

You mean when the engine warmed up, the cat. converter would freeze-up in your
Olds.  How could this happen.  In my 
Vanagon, the cat. converter has the O2 sensor with it.  Could I run the engine
without the cat. converter connected.  I have heard this will not work.  In my
symptoms, the exhaust is continuing to flow out the tailpipe, but it is black,
from an overrich engine, which is also mis-firing badly.  Then, when I switch it
off, and then start it up, the engine runs fine for a while, that then
demonstates the same black smoke again.

Thanks,

Charles