In Reply to: Straight pipe till the muffler, remove catalyzer posted by Dado on April 26, 2000 at 00:12:10:
If you are running more richer, your catalytic converter will become a great big bon fire soon!. The catalyst will melt and your exhaust will become so restrictive, your M3 will just lose power and die on you. And if you're running richer greater than 8% on multiplicative adaptation, it'll set another fault code.
The purpose for the Post 02 sensors is to monitor the efficiency of the catalyst. The signal also provides feedback of the pre-catalyst sensors efficency and can cause the DME to trim the millisecond injection time to correct for slight deviations.
A very interesting thing you've done to your M3!