I have a 95 M3 that is running super rich.
It failed emissions because of High HC and CO content in the exhaust.

My bumper is black and I can smell fuel whenever I back up and the fumes go to the front of the car....

I can't figure out why it would be running rich because this car is bone stock.

I did have a problem with oil in my plug wells, but I put a new valve cover gasket and plug seals in. I stuck the original plugs back in.

I put some fuel system cleaner in the tank and have been running around for 1 week, but the car still looks like it's running rich.

any ideas?

Check your o2 sensors to start. Also possible you've got a vacuum leak of some sort that's making her run rich. Bad thing is if this has been going on awhile, you may have drastically shortened the lifetime of the cat..

Time for a track pipe...:)

Check your injectors out and make sure they're OK and you're not dumping too much gas.

Check to make sure your O2 sensors are still working properly.

Check your vacuum lines behind the intake manifold and behind the fuel rail. These are very common to slip off and cause a leak.

I would think one of these should be your problem, if not, I would do a "check engine light" check and maybe a computer test to see if you get any readings...good luck.

90% certain you have a failing 02 sensor.