Here is a manufacture of high flow cats that look real good but right in post #1 states a "cat simulator" may be necessary to eliminate the cat efficiency codes. I have read elsewhere on other forums that this may be necessary for other high flow cats . This company doesn't make one for my car but I'm sharing it because they are advertising here.."A cat delete option will be offered as well. I would recommend using a Cat simulator to prevent codes." Should high flow cats be avoided ?
.https://www.jaguarforums.com/forum/x...-5-0-a-147158/

Brain fart alert...
I was wrong there..In my lack of knowledge I didn't realize the "cat delete option" is a straight through pipe..no cat at all. Sorry for that but I have actually read a few times where high flow cats were installed and the codes returned..

 

I have high flow cats on my 04 STR. I kept getting O2 sensor faults. Read somewhere here on the forum that you have to space out the Faulting O2 sensors by using drilled out spark plug adapters. I did this and haven't had a single fault since.

 

Have a read here 2003 s type r cat delete - Jaguar Forums - Jaguar Enthusiasts Forum

The downstream O2 sensors are also used for fuelling, spacing them out slows down the response to changes in Air Fuel Ratio.

Fricke is looking at making 300 cell cats which should be effective enough to stop the codes and CEL coming on. If you run 200 or 100 cell then something needs to be done, I personally would not recommend the spacer or minicat solution.

When I put the 100 cell cats on my XJR we changed the emissions settings in the ECU to stop the codes being flagged. This is the better way to do it IMHO...

 

Thank you both for the replies above..Will a dealer change emission settings on an 06 3.0 ? Not likely so who would I look for? I'd like that because the car runs great. The engine spins free,revs up fast with no aspiration problems. As far as I'm concerned the P0420 is telling it might not pass inspection in NY and CA .. It's also a little confusing to me still because my data streams on up and down stream 02 are the same on both sides, my fuel trims are also good but only get the one side P0420. I have to be honest. I was eyeballing those 90 degree extenders on ebay because I read guys with high flow cats use them with success but no reports what happened to their fuel trims.. I called all around today for anyone who had an exhaust analyzer with no luck.No emission test in FL but I'd love to know exactly what is cumming out the back also. I know why they don't have them they're several thousand dollars and up..