Beloved Leader wrote:

lj_robins wrote:

Which part of the emissions test are you failing, CO, CO2, NOx, or
Hydrocarbons?

Hydrocarbons. The last test, yesterday, I missed by 4 ppm at 15mph. The
limit is 55 ppm, and I came in at 59 ppm. Everything else passed. CO %
and NO ppm are great.

Any GM web site or news group should do since the fuel/emissions
systems are the same for all of them. Chevroletforums.com is one. Try
to find a GM factory manual or Mitchell manual since they're much
better than Haynes and Chilton's, especially for fuel/emission
diagnosis. High HC with low CO and NOx points to an ignition problem,
but post all the test results since you may actually have high CO or
NOx even if they're far below legal limits. High CO is a fuel or valve
problem, but high NOx can be from a vacuum leak or very lean mixture,
which can also make HC high. Your state should have an emissions lab
that can answer technical questions or even test the vehicle more
extensively than the typical garage or emissions station can. The lab
here once pinpointed a high HC problem to worn distributor bearings,
something few garages would have caught.

Here's a table I found somewhere. It's more legible with a
nonproportional font, like Courier:


Typical State Automobile Emissions Idle Test Limits
and Performance of Vehicles in Good Working Order


Model Year Typical State Limits Normal Vehicle Emissions

CO HC CO HC
------------------------------------------------------------------

pre-1968 7.5-12.5% 750-2000 PPM 2.0-3.0% 250-500 PPM
1969-70 7.0-11.0 650-1250 1.5-2.5 200-300
1971-74 5.0-9.0 425-1200 1.0-1.5 100-200
1975-79 3.0-6.5 300-650 0.5-1.0 50-100
1980 1.5-3.5 275-600 0.3-1.0 50-100
1981-93 1.0-2.5 200-300 0.0-0.5 10-50
1994+ 1.0-1.5 50-100 0.0-0.2 2-20