Exhaust Gas Recirculation: Description and Operation

GENERAL INFORMATION
The EGR system reduces oxides of NOx in engine exhaust and helps prevent detonation (engine knock). The system allows a predetermined amount of hot exhaust gas to recirculate and dilute the incoming air/fuel mixture. The diluted air/fuel mixture reduces peak flame temperature during combustion.

The EGR system contents:
- EGR tube.
- EGR valve.
- Electronic EGR Transducer (EET).
- Connecting hoses.

OPERATION
The Electronic EGR Transducer (EET) contains an electrically operated solenoid and a back-pressure transducer. The Powertrain Control Module (PCM) controls operation of the solenoid. Exhaust system back-pressure controls the transducer.

- When the PCM energizes the solenoid, vacuum does not reach the transducer.

- Vacuum only flows to the transducer when the PCM de-energizes the solenoid.

When exhaust system back-pressure becomes high enough, a bleed valve in the transducer closes. The PCM de-energizes the solenoid and back-pressure closes the transducer bleed valve. This causes vacuum to flow through the transducer to operate the EGR valve.

De-energizing the solenoid, but not fully closing the transducer bleed hole (because of low back-pressure), varies the strength of vacuum applied to the EGR valve.

Varying the strength of the vacuum changes the amount of EGR supplied to the engine. This provides the correct amount of exhaust gas recirculation for different operating conditions.