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 (NOx).

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 decal.

The EGR system is a differential pressure feedback EGR system. The differential pressure feedback EGR system:
- monitors EGR flow rate by the pressure drop across the metering orifice.
- uses an EGR backpressure transducer as the feedback device.
- controls pressure 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 as a flow metering device.
- allows for a more accurate assessment of EGR flow requirements.