Hello! This is my first post. I would really appreciate some help. My 95 M3 recently failed an emissions test for high HC and NOx at low speed. I put in new plugs, replaced the O2 sensor and put some fuel injector/fuel system cleaner in the tank. It failed again with better numbers, so I decided to replace the cats because of really high NOx (I'm sorry I don't have the numbers but I can post them this evening). I looked all over - prices vary a lot for direct fit and universal cats, but I found a local shop that quoted me $250 for universal Magnaflows installed which was the best price anywhere. When I picked it up I realized that he had installed a two to one (not sure if correct term, but I hope you know what I mean) instead of two cats. I got a Magnaflow part 94008 when I thought I was going to get two 94004s. The car failed again after driving it >150 miles - the NOx was even higher, although the HC almost passed. My question is whether the part he installed is correct for my car. I am concerned about inadequate air flow, and its capacity to remove pollutants. If I can get by on this cat, I understand that I need to drive a while before it really starts working, but isn't 150+ miles enough? Thanks a lot!