Background:
1995 Z28 6Spd Conv
Original / Stock
162,000 Miles
Opti -Replaced 120,000
No Codes
No Smoke
Mobil One Oil Change 160,000
New Plugs
New O2 Sensors
New Air Filter
Techron Cleaner
1/4 Tank of Gas
Location: Maryland

E-Test
Target: (gpm)
HC 1
CO 20
NOX 2.2
CO2 N/A

Results - Original Test FAIL
HC 2.27
CO 39.1
NOX 4.1
CO2 464

Results - Retest #1 FAIL (New Air Cleaner)
HC 2.97
CO 31.5
NOX 2.2 (passed)
CO2 348

Results - Retest #2 FAIL (New AC/Delco Plugs)
HC 3.2
CO 34.9
NOX 2.7
CO2 388

Results - Retest #3 FAIL (New A/C Delco O2 Sensors-2)
HC 3.4
CO 43
NOX 2.6
CO2 403

Things are getting worse. Any suggestions?

 

What mods do you have?

 

Stock

 

Exessive NOX comes from running leaner then normal. Making it run more rich will bump CO and HC. Try cleaning your MAF. Run 20-30 miles on highway just before test on best gas you can find. Drive to different inspection station - away from big cities.

 

The only major thing left that has a direct impact that I can think of would be the catalytic converter. You might consider trying the gallon of denatured alcohol trick...

 

MAF Cleaned
Smallest Town Around
CAT - Replacement (Brand Suggestions?) Less Restrictive
"You might consider trying the gallon of denatured alcohol trick" That's a new one to me. Is it pour a gallon in the tank? Anyone had it work for them?

 

I always thought a "punched" worn out CAT would affect CO not all three.

Any other ideas?

 

For reference I passed the emmissions test here no problem with no AIR, no EGR and a straight pipe in place of the catalytic converter. It looks like they measure it differently here but the limit of hydrocarbons (HC) was 220 ppm. I had less than half the allowable.

Any stumbling, hesitation or anything out of the ordinary? I used to drive the car really hard on the way to the testing station to get it nice and hot, it probably didn't do much, I guess it was more for my peace of mind.