Just attempted to smog my 85 Nissan Maxima wagon and although the car seems to be running very well it failed the California Smog II. It had high Nox readings. The technician kind of pointed me to the O2 sensor (I replaced it) and the EGR (I checked vacuum signal from solenoid to valve and checked the valve for obstructions and operation by applying vacuum to it). Looking for other inputs as to what might cause this failure.

dont worry mines will most likely 2 that too lol
p.s get illegal somebody might do it for ya

most likely it's the catalytic converter.

test...sorry

test again

There is another thing that also causes NOx readings to go high. If your cat converter is not doing the job, it will cause it to fail. If you have not had it replaced, it may be disintegrated inside already. Sometimes you could hear the stuff rattling inside.