responsible for the NOX. Having an afc and wide band 02 helps too. If it is too lean your NOX will go up. If it is a smidget rich between 13:1 and 14:7 under load your Nox will be minimal and your HC and CO will not be that much affected. I have passed twice with out egr. Make sure your water temperature is under 190 degrees when it starts the dyno test. If the car gets above 200 degrees on the dyno test it may raise you NOX level beyond passing. The key thing is not to run lean and not the let the car run hot. Both times I tested I failed the first try then richen it up a little via afc and let the car cool off before getting back in line to pass . Phoenix Arizona is just as strict as California.