Exhaust Gas Recirculation: Description and Operation

EGR VALVE VACUUM SYSTEM

The exhaust gas recirculation (EGR) system allows a small amount of exhaust gas to flow from the exhaust manifold into the inlet manifold when the throttle is opened beyond idle and inlet manifold vacuum is normal. This reduces combustion temperatures in the engine to control oxides of nitrogen emissions.


The EGR valve is operated by an integral vacuum actuator that controls a pintle within the valve. The pintle remains closed to prevent exhaust gas recirculation until vacuum is applied to the actuator. The vacuum causes the pintle to open, allowing the measured flow of exhaust gas to enter the inlet manifold.

The EGR system used with gasoline engines remains closed during periods of engine idle and deceleration to prevent rough idle from excessive dilution of the air/fuel mixture. It also remains closed at wideopen throttle to prevent power loss. At other times, it rapidly cycles open and closed to modulate the flow of exhaust gas as required. Under certain circumstances, it may remain fully open to provide the maximum EGR.


The manifold absolute pressure (MAP) sensor measures the strength of inlet manifold vacuum in the EGR vacuum circuit and sends a signal back to the engine control module (ECM/PCM) The ECM/PCM uses the signal from the MAP sensor to control fuel delivery and ignition timing. In addition, the ECM/PCM will adjust the on-off intervals of the EGR valve to correct the flow of exhaust gas into the cylinders if actual vacuum differs from the preferred vacuum as calculated by the ECM/PCM. This provides the required control of oxides of nitrogen emissions while retaining engine performance under all operating conditions.


Vacuum for the EGR system of gasoline engines is taken from the throttle body and routed through a hose to the EGR electronic vacuum regulator solenoid valve. This valve is controlled by the 435 circuit from the ECM/PCM. When the EGR electronic vacuum regulator solenoid valve is energized, the valve routes vacuum to the EGR actuator. The actuator opens the EGR pintle valve to allow exhaust gas to flow into the inlet manifold. When the EGR electronic vacuum regulator solenoid valve is released, the valve vents the EGR actuator to outside air to close the EGR pintle valve