I picked up my XJ about 3 weeks ago and finally got it in for fluid changes and a regular check up. There were some squeaks and rattles I had some concern about as well as a CEL that seemed puzzling.

$500 later I have all new fluids and stabilizers and U-joints as well as a report that a previous owner removed the CAT and had a straight pipe welded in. The milelage has been cruddy, so I'm wondering if this was why. I had always understood that people removed the cat to improve mileage. ?

I found this exhaust http://www.ironrockoffroad.com/Merch..._Code=IR-X_IEK and plan to order it as well as the CAT listed. Any recommendation on the baffled or high flow options as my muffler is shot as well.

 

Are the O2 sensors in place and operating? The rear sensor is probably having fits with no cat in line. These later computer controlled engines really don't benefit from removing the cat- in fact it can harm economy and performance. What sort of mileage are you getting?
Which exhaust you get is a personal preference thing, some like loud and proud, others whisper quiet. High flow is generally a good idea.
I stuck a thrush turbo on mine along with a Flowmaster Cat and I *hate* it. Nasty drone at certain RPM's. The cat is fine but the muffler sucks. Don't get the cheap ones, lol.

 

Speak up, I can barley hear you.

 

I'm around 10mpg at this point. O2 sensor is still in place. I thought this might be the issue with the CEL on in the first place. I just didn't expect the CAT to be absent.

On a good note it drives like new with the stabilizers having been repaired and new U-joints. I just want to get an alignment now along with the exhaust.

I'll make up my mind about the exhaust soon. I have a neighbor I dislike just enough I'm tempted to get a loud one just because me going to work at 5am would be the highlight of his day.

 

Having no cat will definitely hurt mileage, along with being illegal.

I'd replace the cat, they are pretty cheap.

Here are some cheap ones, they even have them with the hole for the O2 sensor.

http://performance-curve.com/thunderbolt-spincat.aspx

As for the Iron Rock Offroad exhaust, I'd avoid it. It lasted 1 winter on my Jeep before rusting out.

I'd also avoid baffled mufflers. They are loud, but the worst part is they rust from the inside. The welds break for the baffles and they rattle and sound like crap. My friends have flowmasters on their trucks and 3 out of the 5 of them have done this. Another one rusted apart after two years.

I recommend getting a stainless steel Magnaflow muffler (also on that site I linked above) or a Dynomax Super-Turbo cat-back for the XJ. The Dynomax cat-back is very easy to bolt on, and is only a bit louder than stock. I got mine on Amazon with free shipping for a decent price. I have 10,000 miles on it now with no issues.

 

And the exhaust adventure continues; it turns out the amount of pipe in front of the cat that was removed makes it impossible for my mechanic to install the converter and muffler, etc. He recommended that I see the custom exhaust guy up the street. And that looks like it will work. I've decided to replace both the o2 sensors while this is all going on as well. The muffler guy is going to build a custom piece of pipe from the manifold to where the cat is supposed to attach.
It's good to know people that do this stuff.