EGR System - Gasoline: Description

Exhaust Gas Recirculation (EGR) is used to reduce oxides of nitrogen (NOx) emissions. This is accomplished by lowering peak combustion chamber temperatures. To do this, recirculated and metered amounts of exhaust gases are reintroduced into engine through intake manifold, where they are mixed with the incoming air/fuel mixture.

Two types of EGR systems are used, depending upon vehicle application. These are vacuum modulated and backpressure. Some engines may also use what is called "pulse width modulation". The ECM turns an EGR vacuum control solenoid on and off many times per second, varying amount of "on" time to vary amount of EGR. For more information on ECM controlled EGR systems, see the appropriate article in the COMPUTERIZED ENGINE CONTROLS section.