If the catalyst is hot enough to consume that last 0.1 percent O2, it will probably knock the HC count down by at least 20 PPM. On my last test the HC reduction on the 15 MPH test was 40 PPM compared to the previous test. Often these M103 engines are near the HC limit with 0.1 percent O2 on the 15 MPH test, but this first test heats up the catalyst so O2 drops to 0.0 percent on the 25 MPH test, and the HC is not as close to the limit.

It's very simple to make a shorting plug for the R16/1 trim resistor to slow the centrifugal spark advance, and take a short piece of 1/8" vacuum tubing, plug it with a slug of silicone sealer and substitute it for the molded piece of tubing at the manifold end of the vacuum advance line to the EZL module to disable the vacuum advance.

You can see how this reduced the emissions on my California ASM test. My primary objective was to get more HC margin on the 15 MPH test, and the side benefit was a dramatic reduction of NOx though this was not an issue with my car.

http://www.peachparts.com/shopforum/showthread.php?p=833484#post833484

BTW. in order for a car to be tagged "gross polluter" the measured emissions have to be about DOUBLE the limit, so your car would be a long way from that if you only experienced a marginal failure on HC.

Duke