So the previous owner modified the exhaust to my 2000 XJ Cherokee. He basically removed the catalytic completely, relocated the muffler before the rear axle, and snipped the wires to the second O2 sensor. He also bored and stroked it to 4.6 Liters, so it's fairly loud, but I can live with that. But the Check Engine Light is eternally on telling me the O2 Sensor is bad, or in my case missing. I would like the light to function properly and possibly alert me to actual events that merit checking my engine.

I don't have regular emissions checks and don't live in California, so my interest hear is simply getting the check engine light to turn off. I have the exhaust system remove right now to install an SYE on the Transfer case, so no better time than the present. Since it's mainly a wheeler vehicle and street use is to get to the trail and random trips around town, I am okay with saving the space by not going up over the axle and out the back. I was considering putting a cat back in it and reconnecting the #2 O2 sensor, but wanted to keep it compact enough to terminate the muffler before the axle. I also considered welding a bung behind the muffler and adding an o2 Sensor, but wasn't sure if that would be enough to fool the computer or if it would cause the computer to incorrectly compensate the engine for the odd readings. If I do re-install the cat, which one is recommended and wouldn't create much restriction. Any suggestions on brands or ones that are smaller that others?

As for fooling the computer you need to determine what resistance the CPU is expecting from the O2 sensor in a good condition, then put a resistor of that value in series with the wire that used to go to it. I don't recall what it is off-hand, but a search should help you find that answer.

I went to Performance Curve and bought a stainless magna-flow cat. I think it was like 99$ brand new. Had the bung welded in for the 02 sensor. Cut out the old one, slid the new one on, clamped it, bam... good to go. You can run any number of mufflers as well. Magnaflow, borla, dynamax, etc... They should all terminate before the rear axle. If you don't want to run the tail pipe you should be fine without it. Might be a little louder in the vehicle because it will terminate under the passenger side rear seat.

That 02 sensor helps regulate the amount of fuel that your engine consumes. If it is getting a bad reading, I am guessing your mileage is pretty poor. Put the new one in, reset the comp and run it.

Whatever you do, put a cat back on. It's federal law

Good to know.....I will get right on that.