EGR System: Operation: Notes

A backpressure type EGR system is used on 2.2L and 2.5L throttle body fuel injected engines. The backpressure transducer measures the amount of exhaust backpressure and varies the strength of the vacuum signal to the EGR valve. The signal vacuum is bled off into the atmosphere when exhaust backpressure to the EGR drops below a calibrated value.

On 5.2L engines, an electronically controlled EGR system is used. The system consists of Spark Control Computer (SCC), Charge Temperature Sensor (CTS), EGR solenoid and EGR delay system (4-Bbl. models).

Venturi vacuum signal is used to control EGR operation on 5.2L 4-Bbl. engines. Because of the low strength of venturi vacuum signal, a vacuum amplifier is used to increase vacuum signal strength to operate the EGR valve. This system uses an EGR solenoid to control EGR valve operation. Some vehicles are equipped with an EGR delay system to prevent EGR operation for about 60 seconds after ignition is turned on.

On California models, an on-board diagnostic system checks the entire EGR system for failures and is activated and monitored only during selected engine/driving conditions to avoid misdiagnosis.

When monitored, the EGR solenoid is energized, disabling the EGR. The O2 feedback system is monitored to see if a change occurs. The mixture should go lean and the system will try to richen the mixture. The SMEC monitors EGR system performance and registers a fault code if the system has failed or effectiveness has lessened, and turns on the "CHECK ENGINE" light.