Exhaust Gas Recirculation: Description and Operation

EGR Valve:

The EGR system operates to reduce oxides of nitrogen (NOx) emissions. When the engine is under load, the EGR valve admits a small amount of exhaust gas into the air/fuel charge, effectively reducing peak combustion temperatures. Greater amounts of exhaust gas are metered in as engine speed and load are increased. The ECM calculates various input information to control EGR valve operation.

PORT EGR VALVE

This valve is controlled by a flexible diaphragm which is spring loaded to hold the valve closed. Vacuum applied to the top side of the diaphragm overcomes spring pressure and opens the valve in the exhaust port, allowing exhaust gas into the intake manifold and thus to the cylinders.

ELECTRONIC VACUUM REGULATOR VALVE (EVRV)

To regulate EGR flow, an ECM controlled EVRV solenoid is used in the vacuum line. The ECM uses information from the following sensors to regulate the solenoid:
1. Coolant temperature.
2. Throttle position sensor.
3. Distributor rpm signal.

The EVRV solenoid utilizes "pulse width modulation." This means the ECM turns the solenoid "ON" and "OFF" many times per second and varies the amount of "ON" time ("pulse width") to control the volume of recirculated exhaust gas.