Another update...weird results:
Took the car to the tuner and had him verify the settings. Everything seemed pretty much optimal but we didn't want to take any chances so he loaded up a stock MDE2 (factory) tune and upped the idle to 1000RPM and we also swapped out the MRT H-pipe for the factory part.
This place is in a different city than the one I originally tested in so I used a different test facility than the first which may or may not play a part in the results...
The test results: FAIL. Now, however, things were quite different:
40KPH:
HC (ppm): 1 (limit 52) PASS
CO (%): 0.0 (limit 0.29) PASS
NO (ppm): 684 (limit 385) FAIL
Curb Idle:
HC (ppm): 1 (limit 150) PASS
CO (%): 0.0 (limit 0.27) PASS
So now the HCs are just dandy, the CO2 is fine but the oxides of nitrogen (NOx) are nearly double the limit and nearly ten times what was sniffed at the other facility (it was 70ppm). Thinking the issue must be timing advance, I went back to the tuner and we looked at the MDE2 file versus his 93-octane tune (which was used during the very first test...) The 93-octane tune had 31-degrees of timing versus the MDE2 timing of 50-degrees at light load. That must be it, I thought, since advanced timing can cause high cylinder temps and NOx formation. So we took a chance of bringing the idle-speed HC back up by loading the 93-octane tune and leaving its 750RPM idle as is. I went back and sniffed again:
40KPH:
HC (ppm): 0 (limit 52) PASS
CO (%): 0.0 (limit 0.29) PASS
NO (ppm): 696 (limit 385) FAIL
Curb Idle:
HC (ppm): 0 (limit 150) PASS
CO (%): 0.0 (limit 0.27) PASS
HCs better still, NOx worse. WTF? We pull timing out and the NOx gets worse? With the 4-cat factory H-pipe in place?
I'm really stumped. I don't think the EGR pipe was affected in swapping the H-pipe. What are the odds the EGR simply stopped working between the first sniff and now? I saw no MILs at all. I'm going to try the same test facility as was used in the very first sniffing to see what they say but if they come back with high NOx, where's a good place to look??