Thats most likely your catalytic converter.

 

UPDATE: Props to sidescrollin; while I was admittedly a little skeptical about air starvation being the cause of my V12 choking at high RPM's I decided to look into it anyway. LOW AND BEHOLD my air filters were trashed. Torn up and covered in black soot, they're toast. And I checked them just about 1000 miles ago and they were fine which is.. weird.

SO. I removed them and went for a drive.

I'm telling you that Jag ran like a scalded cat like I always knew it should. What a rocket compared to before. Now it revs to about 5500 rpm before starting to choke again and surge violently but it pulls hard up until that point. Lots of induction noise but that was to be expected. So I need new filters obviously.

Feeling quite heroic, I returned home only to be welcomed by the rotten egg smell again which I actually hadn't noticed in the past couple days. Plus the cats were making a sizzling noise. (Maybe the eggs were finally cooking?)

So am I dumping fuel?

I didn't think about this before but since I was looking at the cats today I remembered something. I don't know anything about cats but I know that my old xj-s had one cat on each side and this one appears to have two. Thats right, one where the stock one used to be and then another "cat looking device" about 4 inches behind it. I remember in the ad for the car he described this as "newly installed cat-back exhaust" thoughts?

In Summary: Air filters have partially resolved engine power loss and high RPM cut out but not completely. Smell remains after "hard" driving. Idle is still very lumpy. Black soot on air filters and tailpipes. I can feel what I think is a misfire in the exhaust but can't be sure. Ordered a bunch of parts for a major tune up from Jagbits but they aren't here yet.

I know this is a lot of information but I'm in need of some serious help here and I don't know what's important and what's not..

Thank you in advance guys

 

I am trouble shooting a related (maybe?) problem. I am getting string gas fumes in the cab. I have checked everywhere (seemingly) and don't see any leaks. Pressure regulator replaced (non starting issue).

Could this be the catalytic converter? How is the odor getting inside??

There is moisture (blackish) coming out of the exhaust....excess unburnt fuel??

Any input is appreciated folks!! Thanks in advance!!

Bo...