EGR System
The EGR system is electronically controlled by the ECM and consists of an EGR solenoid, EGR valve, exhaust pressure regulator (EPR) solenoid, EPR valve, EGR vent solenoid valve, and vacuum pump.
The vacuum pump provides vacuum for EPR and EGR valve operation. The EGR and EPR solenoids are mounted at top rear of engine as an assembly.
The ECM controls the EGR solenoid to regulate the amount of vacuum at the EGR valve. The ECM controls on-off time (duty cycle) of the EGR solenoid to regulate EGR flow.
The ECM calculates the amount of EGR flow required based on information supplied by the engine speed and throttle position sensors. When EGR flow should not be recirculated back into the engine, the ECM activates the EGR vent solenoid to rapidly vent vacuum from the EGR system.
During idle situations, the ECM energizes (closes) the EPR solenoid to increase exhaust backpressure. Increasing backpressure increases EGR flow to help reduce emissions during idle.