Explaining emmissions
Thread Starter
Melting Slicks
Joined: Sep 2006
Posts: 3,194
Likes: 27
From: Monroe Twp, NJ
Explaining emmissions
Maybe another silly question, but why do some cars fail emissions with all the required equipment and other cars pass with the equipment removed (Cats, air pumps,egr valves). How does putting in a fuel additive, or adjusting timing or richening and exhaust system help. What are the test machines actually looking for?
Le Mans Master
Joined: Apr 2002
Posts: 5,726
Likes: 46
From: Waukesha WI
St. Jude Donor '15
Some cars just run better than others. It depends on the mileage, wear/tear on the parts, day of the week it was built, etc. Some cars have been tuned to be able to pass with no emissions equipment installed - this is very rare if a full emissions test is done and not just an inspection. Getting a car to pass w/o a working catalytic converter (Cat) would be tricky but possible. Generally, any stock car in proper running order should be able to pass.
Most test machines are looking for:
Hydrocarbons (HC) - this would be unburned fuel usually caused by running rich. On some modified engines the cam setup can cause a false rich condition that would cause a fail for this test.
Oxides of Nitrogen (NOx) - Not nitrous oxide (N2O - NAAWWS). Excess NOx is created when combustion temps are too high. Running lean and incorrect timing are usually the causes.
Carbon Monoxide (CO) - I'm not sure how this one is produced.
There are others but these are the biggies that I remember. I'm sure someone will correct me if I'm wrong
Which emissions actually used to determine the PASS/FAIL depends on the state/county.
Most test machines are looking for:
Hydrocarbons (HC) - this would be unburned fuel usually caused by running rich. On some modified engines the cam setup can cause a false rich condition that would cause a fail for this test.
Oxides of Nitrogen (NOx) - Not nitrous oxide (N2O - NAAWWS). Excess NOx is created when combustion temps are too high. Running lean and incorrect timing are usually the causes.
Carbon Monoxide (CO) - I'm not sure how this one is produced.
There are others but these are the biggies that I remember. I'm sure someone will correct me if I'm wrong
Which emissions actually used to determine the PASS/FAIL depends on the state/county.
Le Mans Master
Joined: Dec 2002
Posts: 6,715
Likes: 2
From: Santa Teresa New Mexico
If you look in the back of the smog machine, theres a little (propane tank) like bottle. Its a baseline that is used to compare the gases to coming from the car.
The machine checks to see if the gases match up.
Sometimes the gases in the bottle are off......or low.
The smog tech, can make adjustments to get a pass. Or if they not that hot with the equipment you sometimes get a fail.
Go down the street to another test station and you might get a pass.
Everybody hates the smog test but, its a good test for a buyer to get. It shows that the cars doesn't have any serious problems like bad rings or valve seals, or wornen valves.
The machine checks to see if the gases match up.
Sometimes the gases in the bottle are off......or low.
The smog tech, can make adjustments to get a pass. Or if they not that hot with the equipment you sometimes get a fail.
Go down the street to another test station and you might get a pass.
Everybody hates the smog test but, its a good test for a buyer to get. It shows that the cars doesn't have any serious problems like bad rings or valve seals, or wornen valves.
Last edited by redwing76; Oct 4, 2007 at 11:44 AM.
