1994 XJ 4x4 31in tires.

Would the Nox be reduced enough if I ran 225/75/15 stock tires instead of the 31s on it currently?

 

Not sure about tire size, but once when my '99 was near the line on Nox the smog check guy told me to fill up with 91 octane before the test. It seems to work for me - have had better numbers ever since. Also be sure that your Jeep gets a really good warm up before testing.

 

This may sound a little silly to you Monaca, but you need to replace the O2 sensor that is in front of the catalytic converter. Your hydrocarbons are very low, which tells me that you are burning lean in the combustion chamber. This leads to a higher than normal combustion temp which will generate higher than normal nitric oxides (NOX). Replacing the O2 sensor will make it burn richer and bring the temps down

 

I only seafoamed the motor through the throttle body. Numbers went to 973 / 1014 allowed
and 1033 / 1110 allowed.

1 more emissions test and then it is exempt.

 

Good to hear. When are they going to "adjust" these requirements now that it has all been proven to be a farce? Won't be long and we will have more smog shops than grocery stores. Why? because after spending all the extortion costs
to make your rig pass smog you won't have enough left to buy any groceries anyways.