Having recently failed an emission inspection I installed a new catalytic converter. Not that I know what the numbers mean but I can interpolate and the following applied in my case: The maximum state standard for Oxides of Nitrogen emissions is 2.6 GPM. Mine failed at 3.37 GPM. After I installed a new hi-flow cat with no other modifications, I was down to .20 GPM. I'm very impressed.
When I removed the old cat it sounded like the entire insides had fused into one molten rock that was rolling around inside a tin can. The only reason it got that far down death row is because 1) I was oblivious to the problem and 2) the people at the inspection station could never maneuver my 5-speed on the dynomometer test and it would always abort the Jeep so they had to pass me. Finally I got caught but glad I did. The XJ even runs better now.
When I removed the old cat it sounded like the entire insides had fused into one molten rock that was rolling around inside a tin can. The only reason it got that far down death row is because 1) I was oblivious to the problem and 2) the people at the inspection station could never maneuver my 5-speed on the dynomometer test and it would always abort the Jeep so they had to pass me. Finally I got caught but glad I did. The XJ even runs better now.