Exhaust Gas Recirculation: Description and Operation

The EGR system returns a small metered amount of engine exhaust gasses to the intake manifold where it is mixed with incoming air and fuel. This air/fuel/exhaust mixture lowers the combustion temperature, which reduces the formation of oxides of nitrogen (NOx).

Exhaust gas recirculation is controlled by an EGR control valve. The EGR control valve is installed ``in line'' in a passage between the exhaust manifold and the intake manifold. The EGR valve is controlled by a ported vacuum signal, taken from the intake system. This vacuum signal is modified depending on the vehicle, to control the amount and timing of exhaust gas recirculation.