Time for New Exhaust on 88XJ

My muffler has rusted through around the outlet to the tailpipe. Inspecting the the tailpipe, it too can use replacement as the welded hanger is about to scab loose and the outlet has been eaten away over the years. I'm thinking about replacing the cat and getting everything done in one shot, although visually, the cat looks good and rapping on it produces no sounds of loose parts. I've had the vehicle for 12 years and ~100K miles, and have not needed any exhaust repair up to this point (250K on the clock).

I'm just looking for stock replacement parts. A question I have looking at the various auto parts web sites is in regards to the cat. There are two versions listed; one with an air tube kit (but requires a separate flange to the down pipe), and one with the flange welded onto the cat inlet port, but no air tube kit. The cat currently on my XJ is of the latter design, although since I got the XJ with 150K miles, I have no idea if it is stock. Can someone tell me what the air tube kit is for and what the vehicle came with stock?

Any suggestions on stock replacement parts?

Are you sure they arent talking about an o2 sensor bung? If so, I don't think you need it for an 88. They have just one in the exhaust manifold.

No, its not the O2 sensor bung. You're correct in that the sensor is on the manifold. The cat equipped with the air tube kit has a tube coming out between the upper and lower heat shields that runs parallel to the cat. The tube looks like it might mate to a large diameter vacuum hose; maybe like a half inch. Here's a link to a pic on AZ'z web site.

My old 90 XJ did not have an air tube on the cat. I don't recall seeing an air tube on any XJ that I ever looked at.

Mine has that little tube. Nothing connects to it. I have had two installed at a shop, both times they have had the tube.

87-90 XJ never had an air tube on the OEM cat.

What's it do? I never looked close at the one I had removed.

Some cars had an air blower that pumped extra air into the cat converter (through the tube), extra oxygen to improve converter combustion of excess unburned fuel. Some muffler shops may use and stock the one with tube as a universal to reduce inventory. Then they just weld it shut on rigs that do not use it.

Thanks for your responses. I'll go with the one similar to the one currently mounted (no tube).