>- the troubles start once it warms up. Greasy black matter coming with
>the exhaust, fumes that make my eyes burn.  I've done some highway 4th-gear
>running with it and while there's plenty of speed/power, there's also plenty
>of smoke. That part in particular gives me the willies. I pulled the oxygen
>sensor today and it was caked with soot. There is another on the way, but
>I'm afraid of destroying it. Fuel economy is very poor.

Stop driving it at once! An overly-rich condition will result in
unburnt fuel passing into the catalytic convert where it will add to
the combustion at very high temperatures, elevating them ever further.

You risk melting the internal components of the "cat".

Diagnose, fix, then drive. Any other order of this procedure will end
up being expensive.

Good luck,
Dave
--
Dave Carpenter

Whatever you wish for me,
May you have twice as much.