Hey there, I have an 04 6 cylinder 3.3 XE there is a little over 200k on odometer and timing chain was changed at 188k, so a yellow sticker under the hood says. I bought this truck for my ole lady 2 years ago from a parking lot sale. You know, the parking lot where you will find a new vehicle for sale every other week or so? This came from a dude, that got it from a dude that gets vehicles from auctions, fixes them with minimal effort and then gives them to the dude I bought it from so he can sell it for him and make a tiny profit. So the story goes. Any how, when I test drove it 2+ years ago, everything seemed "fine." The only thing I noticed that was awkward to me was the steering was stiffer than I'm used to. I can't tell if that's a normal thing with Xterra's or not, but it never bothered my ole lady (Sarah) the whole two years she drove it. Now, I never drove her truck, as I have my own, so I didn't experience any growing problems, and she never gave me a heads up until she broke down on the side of the road, and limped it into a crummy neighbor hood. I did some quick googling so that I could come rescue her, and bought a MAS en route. I got to the vehicle, turned it over and it sputtered violently hard until it stopped, and coughed up some thick black smoke out of the intake box. I'm not a mechanic, but I determined right there I had some sort of restriction. I threw the MAS in anyway, got it to run by feathering the crap out of the throttle, and got her home. I started working on research and came here for answers. Along with this club and other opinions on the web, I did the temp test up and down stream of the cats. On the two manicats, I was getting around 700 up and 500 down. I didn't see relevant change on the other two, downstream cats. I decided to remove the two manicats and downstream cats. That was a fun... When I finally got them out, I pulled the o2 sensors out to inspect them and they were severely damaged. I didn't see any obstruction in the mesh in the two manicats, and the two downstream cats had no mesh. I live in Cali so these had to come out anyway, and get replaced with the CARB compliant ones. Any how, here I sit with all four cats out of what is now "my X" and I'm waiting on new ones to arrive in the mail. My main question for today is, can anyone give me a list of all possible causes for a catalytic converter failure, and can anyone shoot me in the right direction of which parts I should think about replacing? Thank you, my friends, I appreciate all that view and offer suggestions and opinions.