State and federal laws limit the amount of emissions produced by your car. Isolating the problem that is causing unwanted or illegal emissions can sometimes be a difficult task. You should first get an emissions test at an official test centre to get the actual measurements of the pollutants your car is producing. Depending on the exact type of emission, there are many possible repairs to fix the problem.
Determine if the emission problem is illegal. All cars emit a certain amount of pollutants. Drivers sometimes will mistake water vapour coming out of their tailpipes for smoke. Take your vehicle to a test centre that is officially authorised by your state's department of motor vehicles. A list of centres can be found on your state's department of motor vehicles website. Documentation on the various standards can be found at FindLaw.com. The three major pollutants are carbon monoxide, nitrous oxide and hydrocarbons.
Diagnose the cause of the illegal emissions. Excessive levels of carbon monoxide are caused when your engine does not properly burn fuel. According to SmogTips.com, this is typically caused by a faulty sensor or a dirty air filter. Check your oxygen, manifold and throttle sensors as a starting point. You also might just need a tune-up if your spark plugs are not firing properly. Excessive nitrous oxide levels can be the result of a problem in your fuel delivery system. Check to see if there are any vacuum leaks or defective fuel control components. It might also be caused by a faulty exhaust gas recirculation system or catalytic converter. Excessive hydrocarbons can be the result of a malfunction of your ignition system or fuel control system.
Start with a simple tune-up. This can often fix your car's emissions problem. Change the spark plugs, the distributor cap and the rotor. You should also replace the air filter with a new one at least once a year. Get an emissions retest to determine if this fixes the problem.
Isolate the problem. If a tune-up fails to curtail your excess emissions, you might have a more complicated engine problem. If you have a newer model car, your mechanic should be able to run an electronic diagnostic test to see if it produces any errors. If this doesn't isolate the problem, start with simple repairs and work from there. Check to see if there is a coolant or transmission fluid leak from any hoses that are leaking into the combustion chamber. Check the valve seals on your combustion chamber to make sure they are tightly sealed. If the problem cannot be detected by any faulty sensors, ignition or fuel delivery problems, your car might have an oil leak within the engine block. If this is so, a timely and expensive rebuilding of your engine might be in store.