Exhaust Gas Recirculation Valve
An EGR or exhaust gas recirculation valve is used on gasoline and diesel engines to reduce the amount NOx or nitrous of oxides released into the atmosphere. When nitrogen and oxygen are combined with high cylinder temperatures this harmful NOx gas is formed.
The EGR valve reduces the amount of NOx by recirculating a small amount of exhaust into the intake. It is a controlled opening between the intake and the exhaust. By mixing this inert gas into the air fuel charge the cylinder temperature is reduced. Reducing the temperature reduces the amount of nitrous of oxides produced in the chamber. This prevents the engines cylinders from reaching damaging temperatures and protects the environment from NOx.
There are different types of EGR systems used on different engines. The vacuum operated EGR valve used in the illustration above is a typical design. The valve is opened by vacuum supplied through a duty cycle solenoid and closed by a spring. The solenoid controls the valve to open in proportion to throttle opening.
The valve remains in the closed position when the engine started, at idle, and at wide open throttle. A faulty EGR valve or related component may leave the valve in either the stuck open or stuck closed position. The symptoms of a stuck open EGR valve are a rough idle with a lean air fuel mixture. The engine will behave as if it had a major vacuum leak. The symptoms of a stuck close EGR valve are an engine that has pre-ignition ping and knock. This is the result of high cylinder temperatures caused by the lack of the cooling exhaust gas introduced into the chamber by the EGR.
