Exhaust Gas Recirculation Valve
The EGR system includes the EGR valve and the tubing and passages between the exhaust and intake ports. The valve is controlled by the PCM according to input from various sensors. Its main function is to reduce the amount of the harmful gas NOx or nitrous of oxides created in the combustion chamber. When nitrogen and oxygen are combined with high cylinder temperatures, this gas is formed. The EGR valve reduces the amount of NOx produced by recirculating a regulated amount of inert gas (exhaust) into the intake manifold. This inert exhaust gas reduces cylinder temperature; this reduces the amount of nitrous of oxides produced in the combustion chamber.
There are different types of EGR systems used on different engines. A vacuum operated EGR valve is shown in the illustration. The valve is opened by vacuum controlled by a duty cycle solenoid and closed by a spring. It opens in proportion to throttle opening. By mixing inert gas into the air/fuel charge, the cylinder’s temperature is reduced. This prevents the engine’s cylinders from reaching damaging temperatures and protects the environment from NOx.
Vehicle manufacturers have their systems programmed for a certain regulated amount of flow. If this flow is changed, drivability and performance will be affected. It will also set a fault code in memory and illuminate the check engine light. Before replacing the valve, make sure the engine’s injection and ignition timing are correct. Check the vacuum supply and solenoid on vacuum operated valves and check the power supply and ground on electronically controlled valves.