Car wont Pass Smog

[Saul325is]

At 25mph the car passed, but at 15mph the car failed. It says I have high Nox@15mph and high HC@ 15mph. What do you guys think? Oxyegen sensor? I mean if 25mph smogs perfectly, I think its a bad oxygen sensor or cat. I have mustang injectors and an M30AFM but they are tuned appropriatly and are not the problem. Also, what is the part number for the mustang oxygen sensor that i can get for my 87 325is as an alternative to buying a Bosch oxygen sensor for my car.

Thanks,
Saul

[Jon325i]

I don't know the part # for the O2 sensor alternative.

Couple questions....

1. you warm up your car sufficiently prior to the test?

2. how's your oil? having fresh oil will improve your chances of passing

With the mods you have in place now (M30 AFM, Mustang injectors, chip) was your car able to pass smog before with these changes in place?

Jon