I tried to pass my car yesterday. The CO and HC were near immeasurable levels. But the NOx was insane. 3600ppm!

The car runs ethanol fuel. But it's been very recently tuned. No

I tried to pass the car on gasoline a while back, and at that time, the car had little to no NOx and was failing CO.

Could a fuel switch be all that it takes top mess this thing up?

 

What changes did you make after you switched fuels? What do you mean "tuned"? Like tune-up tuned? Or like you modified the fuel system to flow more fuel and then remapped your fuel calibration tuned?