Exhaust Gas Recirculation: Description and Operation

Purpose
Exhaust gas recirculation is used to reduce oxides of nitrogen emissions in the vehicle exhaust. EGR system uses partial recirculation of exhaust gases from a port in the cylinder head to a port in the intake manifold to lower combustion chamber temperature.

Operation
When engine coolant temperature is above 176° F (80° C) the thermo valve closes of the vent port. This in turn allows ported manifold vacuum to be applied to the EGR valve diaphragm.

The EGR valve controls the flow of exhaust gas in response to ported vacuum. At partial throttle settings ported vacuum is high and the EGR valve is open. At full throttle and idle port vacuum is low and the EGR valve remains closed.