Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation System:

The Exhaust Gas Recirculation System controls the formation of NOx (Oxides of Nitrogen) emissions by recirculating some of the exhaust gases back into the combustion chamber through the intake manifold.

The EGR is controlled by the ECM and the EGR modulator. The ECM controls the vacuum supply to the modulator by opening or closing the vacuum switching valve. In conjunction with the vacuum from the VSV, the modulator requires a specific value of exhaust back pressure to regulate the opening of the EGR valve. Vacuum is allowed to the EGR valve during acceleration and under high load conditions, but shut "OFF" upon deceleration or at steady engine speeds.

The diaphragm mounted in the EGR modulator operates by the exhaust gas back pressure to open and close the valve. This opening and closing action of the EGR modulator regulates the vacuum transmitted to the EGR valve. Under a low load condition, such as deceleration, the exhaust back pressure is low causing the diaphragm in the EGR modulator to be pushed down by spring force. This force opens the modulator valve, venting the vacuum passage to the atmosphere.

As the vacuum signal transmitted to the EGR valve becomes weaker, the EGR valve begins to close. As a result, the amount of recirculated exhaust gases to the intake manifold becomes less until completely shut "OFF."

Under a high load condition, such as while accelerating, the exhaust back pressure is high. The high exhaust back pressure pushes up on the diaphragm against spring pressure and closes the valve. The vacuum is then transmitted to the EGR valve, opening the valve, and allowing more exhaust gases to be recirculated into the intake manifold.