Exhaust Gas Recirculation: Description and Operation

EGR Valve Flow:

The Exhaust Gas Recirculation (EGR) system is used to lower NOx (Oxides of Nitrogen) emission levels caused by high combustion temperature and excessive oxygen. It does this by decreasing combustion temperature and displacing oxygen.
The main element of the system is the EGR valve mounted on the intake manifold and operated by vacuum. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber.
The EGR valve is opened by vacuum to let exhaust gas flow into the intake manifold. The exhaust gas then moves with the air/fuel mixture into the combustion chamber. If too much exhaust gas enters, combustion will not occur.
For this reason. very little exhaust gas is allowed to pass through the EGR valve The EGR valve is usually open during warm engine operation when the vehicle is above idle speed.