Exhaust Gas Recirculation: Description and Operation

PURPOSE
The Exhaust Gas Recirculation (EGR) system is designed to:
- reintroduce exhaust gas into the combustion cycle.
- lower combustion temperatures.
- reduce the formation of Oxides of Nitrogen (NOx).


OPERATION
The EGR valve is vacuum actuated. The vacuum hose routing diagram is shown on the Vehicle Emission Control Information (VECI) decal.

The amount of exhaust gas reintroduced and the timing of the cycle varies by calibration. Timing and volume are controlled by the following:
- engine rpm
- engine vacuum
- exhaust system back pressure
- engine coolant temperature
- throttle position






The EGR system is a Differential Pressure Feedback EGR (DPFE) system. Differential pressure feedback EGR is a subsonic closed loop EGR system. The differential pressure feedback EGR system:
- monitors EGR flow rate by the pressure drop across the metering orifice.
- uses an EGR pressure transducer as the feedback device.
- controls pressure that is varied by the valve movement using vacuum output of the EGR vacuum regulator solenoid.
- uses the EGR valve only as a pressure regulator, rather than a flow metering device.
- allows for a more accurate assessment of EGR flow requirements.

Pressure drop is varied by the valve movement using the vacuum output of the EGR electronic vacuum regulator solenoid.