My van failed the NO part of the CA Smog Test twice.
I had the van worked on in between so I'm wondering what is causing the
high NO. The 15 MPH 2200 RPM readings were as follows:

Test 1: %CO2=14.5  %O2=0.6  HC PPM Max=131 Measured=131  CO% Max=0.87
Measured = 0.37  NO PPM Max=1085 Measured = 1492

I installed a new O2 sensor and a new catalytic converter. Also, a good
local mechanic found that the vacuum retard port on the distributer had
been disconnected and that the timing was set at 19 degrees too far
advanced. They reconnected a vacuum hose to the retard side of the
distributer and set the timing back to spec. However, it failer NO again,
this time even worse.

Test 2: %CO2=14.9  %O2=0.4  HC PPM Max=131 Measured=40  CO% Max=0.87
Measured = 0.04  NO PPM Max=1085 Measured = 2131

The reduced HC & CO readings show me that the new cat and O2 sensor are
doing their jobs.

What is causing the higher NO reading? Did retarding the timing make it
worse? Does anyone have any suggestions?

Otherwise, my next move is to remove the vacuum retard hose again, advance
the timing 19 degrees, and return for Test #3. Since I now have made
the "Gross Polluter" class, my Max NO limit got bumped to 2050.

Thanks,
Walter
1985 Vanagon 1.9