Part 1. The Emission Test
The emission test portion is only applicable to 1999 & older cars, trucks, SUVs and motorhomes. 2000 & newer vehicles (except vehicles 14,000 GVWR or greater) are exempt from the Emission Test portion of the smog inspection.
First let's learn about smog. Smog is formed in our atmosphere when nitrogen dioxide and hydrocarbons (HC) react together in sunlight. The internal combustion engine produces, among other gases, nitrogen oxides (NO), carbon monoxide (CO) and carbon dioxide (CO2). CO2 is not a problem, however when combined with nitrogen, it becomes a component of smog.
In an effort to reduce the formation of smog, we need to ensure our engines' are emitting the least amount of hydrocarbons, carbon monoxides, and nitric oxides into the atmosphere.
We must point out that the emissions test portion of the smog check process is where vehicles fail most. A properly maintained engine should not have any trouble passing the emissions test. However, vehicles which are not, very often produce harmful emissions past the state's allowed limits, and subsequently fail this test. Simple timely engine maintenance will eliminate emissions failure causing problems.
The emissions test is only one part of the entire smog check process. Remember there the visual test and functional test sections of the smog inspection also. These two test will be administered after the emissions test.
The Emission Test: The first test the smog check center will administer as part of the entire smog inspection process is the emissions test. In order to pass the emissions test portion of the smog inspection your car's engine must be burning fuel efficiently, insuring hydrocarbons in it's combustion chambers are thoroughly spent.
Hydrocarbon is raw gasoline. The more gasoline your vehicle's engine combusts completely, the less pollutants are emitted into our air.
The emissions test will measure your vehicle's HC, CO and NOx production, and ensure they are within the limits set by the State of California. Your vehicle's CO2 and O2 emissions are measured as well, however these results do not effect passing or failing the emission test.
Optimum fuel combustion is achieved when the engine can maintain a 14.7:1 air/fuel ratio during the combustion process with a constant variation +/- 5% to assist the catalytic converter operation. 14.7:1 air/fuel ratio ensures your car is not burning or wasting fuel. If you notice your car is using up or burning too much gas, more then likey your vehicle's air to fuel ratio is rich.
Performing routine tune ups, which should include changing the spark plugs, air filter, fuel filter, and engine oil, either just before an emissions test, or as required by the vehicle's manufacturers will greatly improve your chances of passing the emissions test.
Dynamometer Used: Counties in California with greater smog pollution require vehicle owners complete the Enhanced version of California's emissions test. The Enhanced smog test requires your vehicle to be driven on a dynamometer while the smog machine collects emission samples from the tailpipe. The Enhanced smog test has been proven to retrieve a more accurate sample of a vehicle's emissions output, then it's predecessor, the Basic smog test. The Basic smog test requires vehicles to be tested, only at idle and 2500 rpms. No dynamometer driving required.
If your county is in the Bureau of Automotive Repairs Enhanced list, no need to worry. There is nothing to do on your part. The smog stations in your area will be equipped to handle your vehicle's emissions test. Only thing you should consider is insuring proper tire inflation and avoid smog checking on rainy days.