Exhaust Gas Recirculation: Description and Operation

Fig. 28 Exhaust gas recirculation system.:

This system, Fig. 28, is used to reduce oxides of nitrogen emissions by lowering the peak combustion temperature in the engine. This is accomplished by introducing a metered amount of exhaust gasses into the intake manifold at throttle positions other than idle.

The EGR valve is mounted on the intake manifold and is used to control the amount of recirculated gas. The recirculated gasses are drawn into the bottom of the intake manifold riser, through the exhaust manifold heat stove and to the EGR valve. The EGR vacuum diaphragm is connected to a timed signal port at the carburetor flange.

As the carburetor throttle valve is opened, vacuum is applied to the EGR valve diaphragm.