Exhaust Gas Recirculation: Description and Operation

PURPOSE
Exhaust gas recirculation (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.

Reintroducing exhaust gases into the combustion chamber reduces combustion temperature, with an attendant reduction in NOx content.

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 regulated by the EGR valve which, in turn, is controlled by the ECM via the EGR vacuum controller. The vacuum controller is supplied, by the ECM, with a signal which is a function of the engine speed, load and temperature. Combined with the ambient pressure and the pressure in the intake manifold, this signal is converted into a control pressure signal which operates the EGR valve via a vacuum hose.