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 nitrous oxide.

The amount of exhaust gas reintroduced and the timing of the cycle varies by calibration. Timing and volume are controlled by:
- engine rpm.
- engine vacuum.
- exhaust system back pressure.
- engine coolant 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.
- uses a differential pressure transducer as the feedback device.
- allows for a more accurate assessment of EGR flow requirements.
- controlled pressure is varied by the valve movement using vacuum output of the EGR vacuum regulator solenoid.
- the EGR valve serves as a pressure regulator rather than a flow metering device.