[Shotimes] High NOx on Smog Test - Need Ideas

[Alan Fanning]

I have one of the SHOShop 3.2l, high compression, engines in my '91 SHO. It
has stage 1 cams, 80 mm MAF/LPM, and a history of failing smog tests unless
the cats are brand new. I bought it 2 years ago from the original owner, who
had spent way too much on SHOShop parts and services.

In prior years, th smog tests here were performed at idle and 2500 rpm,
under no load. Only HC and CO were tested. The car had big problems with the
idle test, which I ascribed to too much valve overlap due to the cams. At
2500 rpm it ran fairly clean.

Fast forward to yesterday - with my registration expiring today, I had
procrastinated as long as I could over getting another smog test. The tests
are now done on a dyno, at 15mph and 25mph. I found a guy who would do a
pre-check (results don't go to DMV) for $25, and was willing to experiment a
little with which gear to run the car in. You have to be within a 1500-3000
rpm window. I figured running at the higher rpm's, like before, would be my
best chance. However, now they also test for NOx, which proved to be my
downfall this year. The good news - HC and CO were nowhere near the limit.

At 15mph and 25mph, the NOx limit is ~750ppm. I tested at 1064 ppm at 15 mph
and just under the limit at 25 mph. The car throws no KOEO codes - I haven't
checked the KOER codes.

I know that the higher compression (10.5:1) and cam's can't be helping my
cause, but can't readily change either at this point.

What else should I check besides the following?

o   EGR operation
o   EGR passageways in intake manifold
o   KOER codes

Also, there's a shorting plug on some connector that can be pulled to
affects NOx? Anybody remember the details on this?

Thanks.

    Alan