I think my XJ has three cats. I see two off the manifold with O2 sensors before and after, and then there is what looks like another on the bottom just before the muffler.
I'm wondering, is the bottom one a cat, or is it just a resonator? It is flanged at both ends, so I am thinking of having a straight pipe built with flanges so I can easily swap between the pipe and cat for off-road purposes.
Since I already have two cats inline, I'm thinking that swapping in a straight pipe shouldn't make it any louder, the only effect should be an increase in performance. Has anyone done something like this on a three cat system and what were the results?
The one close to the muffler is probably a resonator. I don't think anyone would use that many cats unless a previous owner had emissions problems and tried to pass by adding cats. Either way, from my experience, removing a cat makes for a pretty big difference in exhause volume, but that is because the exhaust is flowing better, which is why it increases performance.
All 3 are cats. You can tell the 3rd one is a cat because you should be able to see an o2 sensor before and after it. Replacing it with a straight pipe would be possible as long as you don't have emissions inspections where you live. You would need to buy an o2 sensor simulator for the rear-most sensor though or else the computer will detect the missing cat and you'll get a check engine light.
I know if i did that here in NY it would never pass inspection though.
The problem with the whole 3 cats is that the 4.0 engine is a dinosaur....no offense, its the most durable engine on the market as far as I'm concerned, its very dirty and the only way Chrysler could get it to meet California emissions was to add the two cats up by the manifold to 'clean' it up (I mean steal a little more power away!) That is the reason why it is not in production anymore, I guess too much retooling and designing to make it more efficient.
Dodge/Chrysler/Jeep Technician 14 Years
ASE Master Certified
L1 Advanced Engine Performance
What's not in production anymore? The 4.0? I beg to differ. It is still the standard engine on several of the newest models of Jeeps.
What he means is that it's being phased out right now. The 4.0 is available on only one current Jeep model, the TJ, which is actually Jeep's oldest model right now. When the new Wrangler comes out next year the 4.0 will be gone forever.