I've done quite a bit of searching on this forum and other forums on emissions information. Granted every state (and counties in that state) has different standards (if any at all) on what is acceptable and not acceptable and limits on what amount of gasses can be produced. Hopefully this can become a technical and definitive post on what the emissions numbers mean and what they are (legal limits for various years) in a state.

First, the info I have personally is for NJ (Toms river area). 1992 Camaro. This is in ppm and % (percentage of exhaust gas).

NOx - 907 ppm
HC - 120 ppm
CO - .67%

Those are the three you get tested against in NJ. I'd be interested to see if anyone got other "standard" numbers in NJ this year that differ from those.

Now, what the hell does that mean when you fail? I dont know definitively but the following is what i've gathered from every resource available to me.

NOx is produced by any combustion, if you fail for this, it's more than likely the result of too much fuel being burnt at the rpm you're being tested at. The reason for the additional burnt fuel can be a few different things. EGR being primary, a functional EGR has been shown to drop NOx readings down over 50% of what it failed at when EGR was the only factor. Too much fuel pressure, bad O2 sensor or if the engine is heavily modified, something else. I've also been led to believe that timing also leads to NOx emissions. An advanced timing will lead to more burnt fuel and it would lead to burning that fuel at a higher temp.


HC is unburnt fuel. Failing this could mean a couple things. You could have a non-functional CAT, either from low exhaust temperatures (caused by an oversized cat or low thermostat) or no AIR tubes to the cat or no cat at all. Also, bad O2 sensor or spark plugs could lead to unburnt fuel. Any internal engine mods could also lead to this if not matched to the rest of the engine properly (zz4 CAM etc). Timing may also play a role in this emission, too low of timing could result in a higher HC reading since fuel may not have enough time to burn.


CO is produced from combustion. This is mainly to check for cheaters diluting the exhaust with an air pump or air tube bringing in clean air into the exhaust system.


This site has some excellent information.
Emissions Research

My first test failed emissions. I had the the following numbers.

NOx - 1718 ppm (907 allowed)
HC - 133 ppm (120 allowed)
CO - .49 % (.67 allowed)
CO2 - 11.0 %
O2 - 2.8%

My timing was advanced a lot, my air cleaner is dirty and I have no idea if my EGR is functioning or not. My idle speed was manually increased a bit as well. My car was running regular fuel at the time.

According to the info above, I should :
Retard my timing, remove my air filter for the test and get a new one for later, and make sure my EGR is functioning. I should also run regular fuel with a decent amount of alcohol in it.
So far I have retarded my timing (a +2 degrees or so retarded), removed the air filter, and I'm running premium fuel with 10% alcohol. I'm taking the test again monday (in a couple days). I'm running premium fuel instead of regular as suggested above because in many cases, premium fuel is just regular fuel with more alcohol to increase the octane rating, and alcohol burns cleaner. Also, premium with retarded timing should richen the mixture and lower NOx readings, but may increase HC (but the alcohol should offset that). We shall see if it does.

Also, EGR functionality is key to getting low NOx readings, and those are what I failed big time. Testing it as far as i know is done by pressing the diaphram in and listening to the idle of the engine, if it bogs down then it's not clogged and the valve works. The problem is, you have to know how hard it is to press a new working EGR to compare against yours to see if you have to press too hard, also, EGR only turns on when you are in drive, not idle, and not at low rpm. How are you supposed to test this correctly, especially without a vacuum meter.


Please add any suggestions or information to corroborate this data ...add your own state's emissions requirements and your test results, what you did to pass if you failed. Please note if it's ppm or whatever so we can convert. Also note the year of your car and location, and year test was taken.
If we get enough numbers from different states, locations, we should be able to setup a spreadsheet-type page to make this information much easier to get to for those needing to retake the test or take the test in a different state.

 

thats not a bad site, lots of good info there. someone had posted it up here a year or 2 back.

if this does get stickied here, when asking about why you failed, post up all the numbers that they give you & what type of test it was, not just what you failed on.
CO, HC, NOx, CO2 & O2 all mean something to those who do emissions work.

NOx is produced by combustion chamber temps.
when they hit 2500 degrees NOx starts to spike.
with the timing too high it starts combustion sooner which drives up peak pressure. combustion chamber deposits can do the same thing.
on the engine temp part, the engine operating temp has little to do with NOx, from around 120 up to around 250 degrees or so there is little change in NOx production on a car that is running right & everything is working properly on.
the average cat doesn't do much for NOx reduction, about the most i have ever seen a good cat do was around 600 PPM. some of the aftermarket cats
are only good for about 50 PPM on NOx.
manually opening the EGR valve will only tell you if the passages are clogged or not, to see for sure if the valve is getting vacuum you need a vacuum gage, and even then if you throw in a free flowing exhaust system & have a positive back pressure EGR valve it may not be opening.

CO is the amount of fuel the motor is getting.
the higher the CO is, the more fuel going into the motor.
if the CO is too high, HC will go up.
a motor that is running rich can hide a NOx problem.

as far as what the standards are, here in Texas they change from year to year, what was a pass last year may be a fail this year.
i don't know about the other states.

 

Second test update:
Only fixes I made was retarding the timing about 4 degrees (as far as the distributor would let me as it was hitting the coil) and running regular gas instead of premium. Fan was on the entire time and my thermostat is stock. My air cleaner was dirty so i removed it for the test.

in ppm and % of exhaust
As we can see, retarding the timing and using low octane fuel is an excellent combination, though may not be the only one that will have similar results. Ideally O2 should be close to zero, but i'm not sure if 1.8% is high or low.
I know there has to be people getting inspected soon, it would be good to get a lot of datapoints to work with.

 

These numbers are for the 25 mph speed.

Texas
HC = 144 ppm
CO = .92%
NOx = 1014 ppm

New Jersey
HC = 120 ppm
CO = .67%
NOx = 907 ppm

California
HC = 103 ppm
CO = .74%
NOx = 936 ppm

British Columbia
HC = 88 ppm
CO = .63%
NOx = 938 ppm

Ontario
HC = 58 ppm
CO = .32%
NOx = 652 ppm

 

What a joke.

 

wow thats crappy

i guess i am glad to live where they dont care about such stuff

hum

 

Wow, this is what the state of Texas says my 1983 G20 Van can put out with the factory 305 non catalyst setup.

This is what it did with a modified, tuned 350 TBI and dual cats.

15 MPH
Pollutant---Reading---Standard
HC----------50---------332
CO---------0.10--------1.89
NOX--------72----------2490

25 MPH
Pollutant---Reading---Standard
HC----------42---------326
CO---------0.03--------2.62
NOX--------47----------2320