Exhaust Gas RECIRCULATION Description: 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.

The amount of exhaust gas admitted is determined by a vacuum-operated EGR valve in response to engine operating conditions. A Thermal Vacuum Valve (TVV) or Switch (TVS) or an electrically-operated solenoid controls operating vacuum, depending on engine operating temperature to maintain good cold driveability.

There are two types of EGR systems, the Vacuum Modulated (ported vacuum) and the Exhaust Back Pressure Modulated systems. The major difference between the valves is the method used to control how far each valve opens.

The ported system uses a timed vacuum port in the carburetor to regulate the amount of exhaust gas recirculation. The exhaust back pressure modulated system regulates the timed vacuum according to exhaust back pressure level. A special control valve (transducer) within the EGR valve housing acts as a pressure regulator.