Exhaust Gas Recirculation: Description and Operation

EGR Components:

Vacuum Routing:

PURPOSE
The Exhaust Gas Recirculation (EGR) System controls the formation of Oxides of Nitrogen (NOx) emissions by recirculating some of the exhaust gases into the combustion chamber. The exhaust gas in the combustion chamber lowers the peak ignition temperature.

OPERATION
The EGR valve is controlled by the ECCS Control System (ECM) through the EGR Solenoid and by exhaust back pressure acting on the Back-Pressure Transducer (BPT) Valve.
A system is provided which precisely cuts and controls the port vacuum applied to the EGR valve to suit engine operating conditions.
This cut-and-control operation is accomplished through the ECCS Control Module (ECM). When the ECM detects any of the following conditions, current flows through the solenoid valve in the EGR control vacuum line. This causes the port vacuum to be discharged into the atmosphere so that the EGR valve remains closed.
1. Engine starting
2. Low engine coolant temperature
3. High-speed engine operation
4. Engine idling
5. Excessively high engine coolant temperature
The diaphragm mounted in the BPT Valve raises in relation to exhaust pressure, opening an orifice, also allowing vacuum to be applied to the EGR Valve in response to the throttle opening.