New catalytic converter 95 M3
 

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!

Welcome to United Bimmer.

Im suprised the car still failed. Their may be an issue with the car running to rich. If possible have the OBD system scanned for trouble codes. If you know someone with the BMW Carsoft program they can see the live engine data and maybe see why the car is still failing.

OBD code for knock sensor 2
 

Thanks! I did fail to mention that my CEL light has been coming on sporadically when I accelerate to 3000 RPMs along with a temporary loss of power. The code indicates a bad knock sensor (1226). I have the parts but I haven't exactly been excited about replacing it. I'm gonna do both while I'm in there and also replace the fuel filter. I was hoping that wasn't the reason for the failed emissions :)

That is probably why the car is failing. Get that replaced and re scan the OBD system just to make sure.

Well darn
 

OK, I'll give it a go. Thanks so much!