I read through the recommended post associated to my question but couldn't find my answer. If there's a post that will answer it I'd appreciate a link.
My question is I had a remanufactured engine installed in my XJ. After driving it around I heard the familiar sound of the catalytic converter rattling when the engine is at the right rpm. So I talked to a CA emissions refforee because it's a federal XJ in CA. He gave me a good link for state approved CA CAT's for my federal XJ. Because the XJ has relatively low mileage aroubd 140k and in very good condition I don't understand why the cat went bad. I figured seeing how I already put an engine and cat in it I might as well replace the o2 sensors. I can't find federal o2's anywhere for my XJ. Is the cars ecm/computer looking for a Federal o2 sensor or can I run a CA o2 sensor?
Any advice is welcome and thank you.

 

I live in CA. You can use the regular O2 sensors. You have to use the CA approved cat because if it has been replaced recently, they will check the number on it to make sure it is CARB approved, which costs much more of course. The element inside it is ceramic with a platinum coating, and can break, hence the rattle. Now my question is, did he say you have to replace it, or you may want to replace it. Personally, I would change the sensors and if you sniff the tail pipe and it passes, call it good

 

Is your check engine light on?

Make sure it's not the clamps, bolts, hangars or brackets that rattle. Check the entire exhaust system. Also check for any leaks.

As 4.3L XJ says, there are no differences for the O2 sensors. If you replace the cat, you need to use a CARB certified one.

 

To answer your question re why it went bad. Way back maybe late 90's early 2000 Chrysler had a emissions recall or tsb ( I don't remember which) on the rattling monolith problem.

It was a check and if loose replace, not replace them all. The customer was responsible for any parts required other than the cat. As it was emissions, not a safety recall, it's long expired/dead.

So, just fyi it was a somewhat common problem at lower mileage than yours

 

Thank you for your replies.
Well I took the new CA carb legal CAT (Walker part# 82633) in and had it installed this morning. The CAT that was taken off was damaged. You could see through it clearly but if you shook it you could here chunks inside clunking around. So the cat issue has been taken care of. Now as far as the o2 sensors go. I read on the forums that the o2 sensor are different. The post I read said CA o2 sensors are wide band and require a larger bung then the Federal o2 sensor. I want to replace both up and down stream but I can't seem to find Federal o2 sensors. Walker said they only produce one sensor for both and they cover CA and Federal. Down stream 250-24942 and up stream 250-24943. So who is correct? Thanks again for eveyones replies.

 

Then please link the post that concerns you so we can understand what the poster is actually saying.

 

It looks like they are all the same on Repairlink. They show 56041212 as front as 56041213ab as rear. Perhaps they were working on an earlier model?

 

I saw the same thing. I went ahead got the up and down stream. It looks like the down stream is in much better shape than the up stream. Thank you for your input.