the only reason, when removing the cat... the check engine light comes, on is because the PCM is getting the incorrect signal from the rear o2 sensor... it has NOTHING to do with the a/f ratio... yes there is air that is free-er flowing now, but the PCM can adjust to compensate using the first o2 sensor...
if the 3rd o2 sensor i.e. the rear sensor was such an important part of the motor running properly... why was my car running properly while switching between FS tune to Tom's tune? i got a CEL from the rear o2 sensor missing... but the a/f ratio was actually spot on, considering i have stage 2 cams...
yes you are removing emissions equipment. but again, it has nothing to do with how the motor runs... nothing...
and to go even further... when i did my gauge cluster swap, i had to disconnect the fuel sender wire... i eventually got a check engine light, but my car never ran different... it had fuel, and thats all it cared about... it didnt run any richer or leaner...
the PCM is adaptive, and will adapt to whatever is thrown at it, to this best of its parameters...
tom or any of the other tuners will tell you, that when they "disable" the rear o2, they arent changing the a/f ratio or anything, they are just IIRC, removing the code or giving the PCM a false code saying the cat is ok.
basically, the CEL is to take the car to a dealership, so they can take a look at the mechnical side of the car and let you know whats wrong...
how do you know that your car is running richer btw, when the CEL pops up?