what did you do with the O2 sensor after the cat? Does you Jeep ever throw codes?
Thanks
My XJ came like that so I'm not sure exactly. Some sort of piggyback module that gives the computer good O2 readings at all times.
On the TJ it was even simpler. After the cat was cut out, install an O2 sensor bung in the pipe in a similar spot to where it used to be (on the cat) Get your self some spark plug "Non Foulers" under HELP! part number 42009. They have the correct 18mm threads. There are 2 in a package. Take one of them and drill out the hole in the bottom to 1/2". Thread the unmodified one into the O2 sensor hole. Then install the modified one into the first. Thread in your O2 sensor and you're all done.
I guess it's supposed to pull the sensor up out of the exhaust flow just enough so that the increased flow (from the missing cat) doesn't give a big whiff of exhaust gases. You want it to get just a little sniff, just like factory.
This method has worked flawlessly on my gf's 97 TJ 4.0 for a while now. Just be careful where you install the stuff, it's pretty tall and may interfere with the floorboards. This TJ has a 2" body lift so it all cleared fine.