Exhaust Gas Recirculation: Description and Operation

PURPOSE
Exhaust gas recirculation (EGR) (applicable to California market only) reduces oxides of nitrogen (NOx) in the exhaust. NOx are formed at the high temperatures which occur in the combustion chambers at high engine loads.

NOx levels can be reduced by recombusting a portion of the exhaust gas. This is accomplished by directing a portion of the exhaust back to the intake manifold where it is inducted along with a fresh fuel/air charge into the engine. This reduces combustion temperature, resulting in a lower emission level of nitrogen oxides.


OPERATION
The system is not activated when the engine is cold or idling. Under these conditions, the NOx level is already low and recirculation would impair the running of the engine.

Recirculation is controlled by the EGR valve which, in turn, is operated by the EGR vacuum controller via a signal from the engine control module. The signal which the vacuum controller receives from the control module is a function of engine speed, load and temperature.

The EGR valve is operated by a vacuum signal from the controller, based on a combination of air pressure, intake manifold vacuum and the control module signal.