Hi there guys, i wantwd to see who would know or guide me to where i can get the second and third cats for my xjs? Thank you
Are you missing them or are they poisoned / your numbers are off?
What State are you in (and or country)?
Well okay so since you ask, my sequential exploration to resolve the bank B of the engine which is running lean is quite annoying me at this point. So I’m taking the initiative of replacing the excusing manifold gasket, all 3 cats. And see the result. My last resort is replacing or rebuilding the ECU. Im in los Angeles california
That sounds like a very expensive way to diagnose the problem. Hopefully someone will have a better idea.
John you know how there comes a point when youre so annoyed already that both the expensive and cheap are irrelevant and you just need this to be corrected. Well this is the situation. Alrught is check this out maybe you can make sense of this. So the left side (bank B) has a foul smell out of the exhaust which doesnt smell like unburnt gasoline. While the right sides (Bank A) exhaust is fine. So to do some series of process of eliminations, I disconnected the O2 sensor off the left side and sure enough the foul smell started disappearing and the ECU kicked in and the engine started working rich now. So also i had a mechanic tell me that he suspecting exhaust leak as well, which makes me wonder there is possible exhaust manifold gasket damage or something. However i dont have check engine on at all. So what comes to your mind, if anything even does.
Okay, great information.
I’m in Colorado, run a shop that specializes in your car, and as a former native Californian, I can comfortably say your emissions laws which have so nicely been imposed on us, are stupidity in its greatest form, but I digress. 
Being in CA, you have to have CARB certified cats, of which there are none for the 6L, so you’d need to have a shop install the same using universal units. The bill to do so will run you between $3-5k depending on current availability. If upon unhooking the B O2, and it starts fueling correctly, I would recommend replacing that first. A hole in the exhaust manifold stream would need to be very significant in order to cause the O2 to try and compensate, and in your situation, it would actually call for more fuel as more “fresh” air is passing by, but again, that’s a huge stretch.
So, have you replaced the set of O2 sensors, the coolant temp sensor and put fresh NGK plugs in gapped to .025? You need to do all of the above if not or if it’s been thousands of miles and many moons. In addition, cap, rotor and coils.
Second, you need to get the car to a shop and have them actually read the emissions out of both banks. While being sniffed, the full load microswitch needs to be depressed to see if the mixture richn’s up.
Third, which is anecdotal but telling, when the car is warmed up, is the exhaust temp on B warmer than A (beauty of true duals)?
Your ECU is about as bombproof as they come for the XJS line, not saying they don’t fail, but I have personally never seen one cause a rich / lean condition between banks.
Long story short, throwing cats at it is not the place to start, get the car to a healthy baseline (to include an injector service and test of the fuel pressure regulator).
If you have gone down all the aforementioned rabbit holes to bring the complete maintenance up to date, then report back for additional tests.
Here’s the trick, I’m not suggesting throwing parts at the car to rectify an issue, although it obviously can be a side benefit, but I go through 20-30 of these things a year, all different series and vintages, high mileage, low, stored, driven, etc., and they are all of the age now where that baseline needs to be established, regardless of if ohm meters or noid lights give you a good indicator, the lifespan of these bits is ending, it’s hot as hell under that bonnet, and chasing one thing after another without the basics nailed, will drive you to torch the thing and collect insurance. 
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Jack,
The California emissions test were expanded to include a visual verification by the technician that the exhaust components, including all catalytic converters, have the correct OEM part number for your model year car and have been certified for use in California. This is in addition to the gas analysis test. I observed this myself before I moved from California in 2021 when the shop I took our Jaguars to for their smog tests failed a Mazda Miata because the owner recently had an aftermarket catalytic converter installed. The Miata passed the gas analysis test, but failed the visual inspection. I watched uncomfortably as the emissions shop owner called the local shop owner who installed the aftermarket catalytic converter and told him that he had broken the law and there was an angry three was conversation between the shop owners and car owner that continued until I left. Our 1990 XJ-S convertible easily passed its emissions test and I slinked away quietly with the paperwork while the Miata aftermarket catalytic converter discussion continued.
Bottom line, do not plan to fix your problem with aftermarket catalytic converters if you plan to register your car in California. I currently live in South Carolina and our Jaguars no longer are required to have emissions tests and installing an aftermarket catalytic converter is not an issue here or probably in many other states.
Paul
He can install aftermarket cats, no issues, they just need to be CARB certified.
Thanks guys, my issue is that bank B isnt working correctly in the first place. Passing smog is secondary right now, because the vehicle is an arizona register (which i have residency there and have it registered there). i just want the mechanics of the vehicle to be working correctly so that i don’t have that god aweful foul smell which in turn im sure it may be damaging loss of things. However additionally, to add on i has bought a $50 secondary cat grom oreilly and ou that on because i didn’t know any better at the time and thought all cats work the same way. But now as i read more and educate myself i see why there are different ones with different prices. Not that i wanted to be cheap but thought that all of them worked the same. Thanks for all thr input