Ok so the stealership states I need a new cat for my 01 Wrangler. They suggested to replace all 3 (pre-cats and main) at a cost of $1300. But my question is if the O2 sensors are only monitoring the pre-cats, how does the main cat come into play if there are no sensors coming off that converter???? Why cant I just replace the pre-cats and put a straight pipe in place of the main cat? Any help???