Catalytic converter red hot - high exhaust temps rough tune

[gofastant]

So I'm driving the 1990 16V VW around (no supercharger yet). It's got a rough tune but I think I'm heading in the right direction finally. I drive around the block a couple times, maybe 3 miles. When I stop I see smoke coming from under the car....the inlet of the cat is glowing red hot and the muffler is white hot. I then run for the fire extinguisher.

During the drive the AFR was 12.5 - 15, nothing out of the ordinary. The only thing I didn't like was that during off-throttle decel, the AFR was rich instead of lean. Like 12.5 - 13.0.

So I have to wonder, was the off-throttle decel throwing fuel into the exhaust? Overheating cats are caused by excess fuel burning or a blockage. I wonder if it's blocked, which would also be cause for my rough idle. It won't idle smoothly below 1,200 RPM and only pulls 16.5 inches instead of 20.

I'm not driving it until I can inspect the cat. I was just wondering if anyone has seen this before.

[Matt Cramer]

Another possibility would be not enough timing.

[gofastant]

It was only running on 2 cylinders. The other 2 cylinders weren't firing but the gas was getting pumped down the exhaust and burning at the cat. This is why they say to be careful.