My normally reliable '92 400E has become undriveable. It starts and runs Ok when cold and for a little while until it warms up. After it warms up, there's no power, engine misfires, backfires when accelerator is pressed; and if it stalls may not start again until it has cooled off.

The plugs look fine and engine has about 210k miles. Check Engine light is *not* on.

I've searched this forum and the web and haven't found anything that fits yet.

Could a bad catalytic converter cause this behavior?

Any hints / tips on how I can diagnose this problem will be appreciated.

Thanks,
-Forrest