The Exhaust Gas Recirculation (EGR) system reduces oxides of Nitrogen (NOx) in the engine exhaust and helps prevent detonation (engine knock). Under normal operating conditions, engine cylinder temperature can reach over 3000°F (1649°C). The formation of NOx increases proportionally with combustion temperature. To reduce the emission of these oxides, cylinder temperature must be lowered. The system allows a predetermined amount of hot exhaust gas to recirculate and dilute the incoming air/fuel mixture. The diluted mixture lowers temperatures during combustion. The EGR system consists of the following components:
■Electric EGR Transducer (EET)
The electric EGR transducer contains an electrically operated solenoid and a backpressure transducer. The Powertrain Control Module (PCM) operates the solenoid, determining when to energize the solenoid. Exhaust system backpressure controls the transducer.
When the PCM energizes the solenoid, vacuum doesn't reach the transducer. Vacuum flows to the transducer when the PCM de-energizes the solenoid. When exhaust system backpressure becomes high enough, it fully closes a bleed valve in the transducer. When the PCM de-energizes the solenoid and backpressure closes the transducer bleed valve, vacuum flows through the transducer to operate the EGR valve.
De-engergizing the solenoid, but not fully closing the transducer bleed hole (because of low backpressure), 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. This system does not allow EGR at idle.