Originally Posted By: Clevy
Originally Posted By: tomcat27
ODB II systems have O2 sensors after the cats in addition to the O2 sensors before the cats to ensure that the cats are functioning and cleaning up the exhaust. if you eliminate the cats on an OBD II system you have to get creative to keep the MIL off. additionally, you would not pass emission inspection around here.
and while all ODB systems (ok, FI systems) can compensate for changes in backpressure to keep the fuel to air ratio correct, they cannot modify the torque curve unless they also have control over valve timing and intake runners.
The post cat O2 sensors are only to monitor cat is functioning and doesn't affect fueling whatsoever. A tuner will turn them off eliminating the cel.
On the OP's car, likely, but not every car. On my previous STI, the fueling tables were still affected by the post-cat 02 sensor, IIRC. I was actually pretty surprised to see this.