Exhaust Gas Recirculation: Description and Operation

SYSTEM OPERATION

The EGR system is an emission reducing system that concentrates primarily on the reduction of oxides of nitrogen (NOx). The purpose of the EGR system is accomplished by allowing a specified amount of hot exhaust gas to flow from the exhaust manifold into the intake manifold to mix with the incoming air/fuel mixture. This mixture enters the combustion chamber and lowers the peak flame temperature during combustion. This reduction in combustion temperature reduces the possibility of ignition knock and the level of NOx output.

California vehicles are supplied with an on-board diagnostic system for the EGR system. This system has a solenoid that is placed in the vacuum signal line to the EGR valve. The EGR solenoid is used to disable the EGR system so that the SBEC can perform its diagnostic check. This diagnostic check is activated only during select engine/driving conditions, and checks the entire EGR system for failures. The SBEC monitors the EGR system and if the system check shows a failure, the CHECK ENGINE lamp in the instrument panel will illuminate indicating that immediate service is required.

EGR Mounting:

CONTROL VALVE AND TRANSDUCER

The EGR system used is a backpressure type. A backpressure transducer measures the amount of exhaust gas backpressure on the exhaust side of the EGR valve and it varies the amount of vacuum supplied to the EGR valve. The transducer uses this backpressure signal to supply the correct amount of vacuum to the EGR valve depending on engine load conditions. Vacuum is supplied to the backpressure transducer by a ported vacuum signal from the throttle body.


EGR SOLENOID

This solenoid is controlled by the SBEC. The SBEC monitors engine coolant temperature and other operating conditions to determine when to energize the EGR solenoid. When the SBEC supplies a ground to the solenoid (energizing), vacuum is cut off from the EGR transducer. When the SBEC removes the ground from the solenoid (de-energizing), vacuum is allowed to flow through the solenoid and out to the EGR transducer.