EXHAUST GAS RECIRCULATION SYSTEM

The exhaust gas recirculation (EGR) system allows burned exhaust gases to enter the engine intake manifold to help reduce NOx emissions. When exhaust gases are added to the air-fuel mixture, they decrease peak combustion temperatures. For this reason, an exhaust gas recirculation system lowers the amount of NOx in the engine exhaust.

A basic EGR system is simple. It consists of a vacuum Operated EGR valve and a vacuum line from the carburettor. This is pictured in Fig. 31-14. The EGR valve usually bolts to the engine intake manifold or a carburettor plate. Exhaust gases are UM routed through the cylinder head and intake manifold to the EGR valve.

The EGR valve consists of a vacuum diaphragm, spring, plunger, exhaust gas valve, and a diaphragm housing. It is designed to control exhaust flow into the intake manifold. See Fig. 31-15.

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