EGR System - Gasoline: Description

Exhaust Gas Recirculation (EGR) is used to reduce oxides of nitrogen (NOx) emissions. This process is accomplished by lowering combustion temperatures of burning gases. Recirculated and metered amounts of exhaust gases are reintroduced into engine through intake manifold, where they are mixed with air/fuel mixture.

Vacuum modulated system regulates exhaust gas recirculation according to manifold vacuum. Backpressure modulated system regulates timed vacuum according to exhaust backpressure level. Special control valve within the EGR valve housing responds as a pressure regulator.

Some engines use what is called "Pulse Width Modulation". The ECM turns the solenoid on and off many times per second and varies the amount of "on" time to vary the amount of EGR. For more information, see appropriate article in the COMPUTERIZED ENGINE CONTROL section.