Exhaust Gas Recirculation: Description and Operation

EGR System:

PURPOSE
The EGR system operates to reduce oxides of nitrogen (NOx) emissions.

OPERATION
By recirculating part of the exhaust gas into the manifold, combustion chamber temperatures are reduced. This reduction in temperature lowers the creation of NOx (Oxides of Nitrogen). 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. To regulate EGR flow, an ECM controlled solenoid is used in the vacuum line. The ECM uses information from the following sensors to regulate the solenoid:
- Coolant temperature.
- Throttle position sensor.
- Distributor rpm signal.

CONSTRUCTION
The EGR system consists of the following components:
- ECM - controls operation of the solenoid and monitors system for proper operation.
- EGR valve - allows exhaust gas to flow into intake manifold.
- Control solenoid - allows a precise amount of vacuum to flow to the EGR valve, controlling recirculation amount.
- EGR modulator - controls the amount of EGR operation base on exhaust gas pressure.
- EGR temperature sensor - monitors EGR operation for self-diagnostic purposes. For further information, refer to COMPUTERS AND CONTROL SYSTEMS.