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. 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 Control Valve and Electronic Transducer:

CONTROL VALVE AND ELECTRONIC TRANSDUCER

This system has an electronically controlled vacuum solenoid that is an integral part of the Electronic EGR Transducer (EET). The electronic portion of the solenoid receives its electronic signal from the SBEC. The solenoid uses this signal to regulate the amount of vacuum supplied to the EGR transducer. Vacuum is supplied to the EET by a ported vacuum signal from the throttle body. The 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.