Exhaust Gas Recirculation: Description and Operation

The Exhaust Gas Recirculation (EGR) system is designed to:
- reintroduce exhaust gas into the combustion cycle.
- lower combustion temperatures.
- reduce the formation of oxides or Nitrogen (NOx). 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
- air charge temperature
- throttle position

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

The EGR system is a differential pressure feedback EGR 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 located in the EGR tube.
- uses an EGR backpressure transducer as the feedback device.
- uses the EGR valve only as a pressure regulator, rather than a flow metering device.
- controlled pressure is varied by the valve movement using vacuum output of the EGR vacuum regulator solenoid.
- allows for a more accurate assessment of EGR flow requirements