Exhaust Gas RECIRCULATION System: Valve: Operation
Refer to DESCRIPTION - MONITORED SYSTEMS for more information.
The engines use Exhaust Gas Recirculation (EGR) systems. The EGR system reduces oxides of nitrogen NOx) in engine exhaust and helps prevent detonation (engine knock). Under normal operating conditions, engine cylinder temperature can reach more than 3000°F. Formation of NOx increases proportionally with combustion temperature. To reduce the mission of these oxides, the cylinder temperature must be lowered. The system allows a predetermined mount of hot exhaust gas to recirculate and dilute the incoming air/fuel mixture. The diluted air/fuel mixture reduces peak flame temperature during comiustion.
The electric EGR transducer contains an electrically operated solenoid and a back-pressure transducer (Fig 1 ). The Powertrain Control Module (PCM) operates, the solenoid. The PCM determines when to energize the solenoid. Exhaust system back-pressure controls the transducer.
When the PCM energizes the solenoid, vacuum does not reach the transducer. Vacuum flows to the transducer when the PCM de-energizes the solenoid.
When exhaust system back-pressure becomes high enough, it fully closes a bleed valve in the transducer. When the PCM de-energizes the solenoid and back-pressure closes the transducer bleed valve, vacuum flows 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.
This system does not allow EGR at idle.
A failed or malfunctioning EGR system can cause engine spark knock, sags or hesitation, rough idle, engine stalling and increased emissions.