Thanks, David ....

My goal was simply to get this thing running and sell it as a project car for someone who enjoys this particular model car, but this emissions thing is pretty interesting :-)

I am going to replace the O2 sensor since it looked it was installed by a butcher ... I metered the sensor and it appeared to be generating cyclic input for engine computer ... but, that was only at idle and with it being sooty this seemed like best place to start - plus, I don't think I knew enough at the time to chart how big the rich and lean input deltas were.

Since the cat "appears" clean on exhaust side, and with a new O2 sensor, what if I swap cat ends?

Appeciate the advice!

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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg