i have no CAT and my check engine light comes on from time to time but my mechanic rigged the O2 sensor so that it can work...am i losing power with the check engine light on, and if im at the races and i dont have a 10mm to take off the negative part of the battery to take off the check engine light can i still run it hard with the check light on???

 

what do you have to do to you O2 sensor to take the cat out? I was thinking about making a test pipe... any opinions?