Failed emissions

[Tedford]

So to start off, the car(91 318is) is running great, I noticed the car smelling richer lately but didn't think much of it. Took it in for emissions today and it failed pretty bad. Cat was last replaced 7/2013, I'll be doing a good amount of reading this week to figure out where to start but figured I'd make a post here as well. Any help would be greatly appreciated.

HC in grams/miles 1.59 standard 1.0
CO in grams/miles 10.30 standard 12(passed)
NOX in grams/miles 5.96 standard 2.5

[Gerta]

Could be a failed o2 sensor.

[bmwman91]

I would bet that it is a combination of things, including a dead cat. Is the replacement cat an aftermarket one like Catco or Magnaflow? Those have a lot less reactive material to begin with, and running rich will cook them darn quick. I typically need to replace mine every 4-6 years, but had one die after 2 because of a fuel tuning issue.

Does your car warm up fully (temp needle near the middle)?

As Gerta mentioned, a bad O2 sensor can definitely be a culprit too.

[Chuck C]

What do your plugs look like? High HC usually indicates a combustion problem.