Exhaust Gas RECIRCULATION (EGR) System: Description

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

There are two types of EGR systems; ported and exhaust back pressure modulated. The ported system uses a timed vacuum port in the carburetor to regulate the amount of exhaust gas recirculation.

The back pressure modulated system regulates the timed vacuum according to the exhaust back pressure level. A special control valve within the EGR valve housing responds as a pressure regulator.