Leave the cat alone if it's not working you will get a check engine and set codes for the cat .the flowmaster super 44 will be loud enough . and this forum is for jeep cherokee xj 's not grand cherokee's .

 

Never fool with emissions devices, the cat 02 sensor inputs back to the PCM are critical for proper function modding them will cause all kinds of undesirable issues with the powertrain control module and you'd be better off throwing your wallet out in the street when you see what happens to fuel economy.

 

Dont gut the cat, you will lose torque. You dont want that. Leave it as is, or replace it with a high flow.

 

Gutting the cat will give you better exhaust flow, if you live in an area where there is no smog check there is no need to get a high flow aftermarket one, a gutted cat will still pass the visual inspection if you even have inspections, it may set off a check engine light but the rear o2 sensor after the cat is just to monitor the cat and it doesn't affect engine performance like the front o2 sensor does.

 

Okay, it depends whither you have a California emissions or Federal emissions system. The CA system has 02 sensors before and after small cats in the downpipe on each bank and the Fed system has a one in each headpipe and one after the large cat under the trans. With the CA system, the large cat underneath is not monitored but does provide backpressure to make the primary cats work more efficiently. With the Fed system, the large cat is the only functional cat you've got so it can't be modified or eliminated. THIS is where you'll need a high flow cat. You could probably gut the downstream cat on a CA system, but I wouldn't recommend it.

Personally, I think you won't see any significant improvement by gutting the cat. Most of the restriction is in the muffler and the Flowmaster will take care of that. Having said that, I saw significant power gain by running Mr. Gasket's CataClean thru my high mileage 4.0 that's starting to use oil. I'm running a Flowmaster 50 on that.