Well my 2002 135 TF just scraped through on emissions, which surprised the hell out of me, why?. Well last couple of years it has sailed through, but I had been patching the back box, so a few weeks ago I went to replace the back box, but the joint with the cat was one complete lump of rust, so I had to cut it off and replace the Cat as well, and the sensor to be on the safe side. Now, less than 100 miles later, it only just passed the emissions test. What that all about?