Hey Guys, My 1995 XJR has some serious exhaust leaks, to keep it within a budget( I know its a jaguar but its a budget project) If I get a straight pipe welded in with the cats removed and straight back to the stock mufflers, will my performance or engine runability be affected with the fuel/air ratio change caused by O2 sensors throwing codes. Will I gain any performance by doing this?

 

The O2 sensor being fwd of the fwd Cats and in some places in the world after the fwd Cats ( 4 O2 sensor systems ) that aft or mid location Cats are not needed in engine regulation / control as the gas sample has already passed but are needed in final exhaust emissions output gasses in the local testing requirements .

 

I assume it leaks from the middle section? Remove it completely, see how it looks, maybe its fixable? I've patched mine in 4 or 5 places with a pipe sections over old thin metal, wire brushed and painted over, it still fine, 2 years later.

 

I've been running catless for about 2 years when my front pipes rusted out. The CEL is on all the time. I took the underfloor cats out last year when they rusted out as a result of age and ice damage that i documented in another post. Right now I have the mufflers and resonators with straight pipes in between. The downside besides the CEL is slightly worse mileage in the city. In Massachusetts there is no emissions test for vehicles over 15 years old. Below are the pipes i used, much cheaper than ones with Cats.

https://www.jaguarclassicparts.com/u...e-non-catalyst

 

The X300 cars are different to almost every other car, in that the second (downstream) O2 sensor is the main fuel correction, and the one closest to the engine is the check. I don't know how they make it work, but it does.

So if you remove the cats in the downpipe the check engine light will always be on. You can remove the underfloor catalyst and it won't affect the ECU.

The system is quite free flowing, I have removed the cats on a V12 before and it made absolutely no difference to performance or fuel economy.

 

Thanks for the replies! Definately helpful. Will be getting the piped welded in soon then.