There may be nothing wrong with your car. The problem is that CA keeps reducing the cut points - an issue I have taken up with my state legislators and the BAR, but I just get the runaround.

There is no specific NOx control device for your engine. It is all built into the spark advance map, stoichiometric A/F ratio, and three way catalyst.

One way to reduce NOx is to retard the spark advance map. This will reduce peak fame temperature where NOx is formed and increase EGT to make the catalyst hotter and more effective. If the cat is working at peak effectiveness the measured O2 content should be zero.

I can tell you how I do this on my '88, but I'm not sure if your car has all the same systems. On my car the initial timing is not adjustable so I:

1. Block the vacuum advance line to the EZL ignition module

2. Use a short piece of wire to short the R16/1 resistor socket

This considerably cuts the spark advance at low engine speed and moderate load resulting in so little engine torque below 2000 the car will barely get out of it's own way, but it significantly reduces both HC and NOx, and my tests read zero O2.

Search under my handle the words - R16/1 resistor- as I have made numerous posts over the past ten years about how emissions are created and controlled and how to make KE systems pass when there are no specific indicated faults in any system or component.

I did emission control research for GM early in my career, so I know the ropes.

Duke