It is illegal to tamper with emission-control devices. An emissions check can also alert you to an emissions problem. Pay attention to a loss in fuel economy. This usually signals an increase in emissions. Black smoke means there is too much gas in the air-fuel mixture and the fuel injection system should be checked.
Blue smoke means the engine is burning oil and too many hydrocarbons are being released.
Check any fluid leaks from your air conditioner immediately. Federal law requires that your mechanic recycle CFCs removed from the air conditioner during repairs. Pay attention to dashboard lights that warn of engine problems. If a warning light comes on, find out what's wrong and fix it. Keep your radial tires properly inflated and ensure tires are properly aligned.