Exhaust Gas Recirculation: Description and Operation

EGR Back-Pressure Variable Transducer (BVT):

EGR Valve:

PURPOSE
The Exhaust Gas Recirculation (EGR) system recirculates exhaust gas to the engine intake system to reduce combustion temperatures and exhaust gas Oxides of Nitrogen (NOx) content.

OPERATION
The amount of recirculation varies from zero with a cold engine to a fixed flow rate with engine at operating temperature, intermediate load, and 1500 rpm minimum engine speed. The flow increases steadily as coolant temperature rises past 158°F (70°C). The system employs a control solenoid, triggered by the Electronic Control Assembly (ECA) and sensor system. The ECA will disable the EGR system under conditions of zero throttle opening, full throttle, low coolant temperature, low engine speed, transmission in neutral, or system malfunction. The ECA controls the EGR system by opening and closing the EGR control solenoid.

EGR is only on when the ECA and sensor system open the EGR control solenoid, allowing vacuum to close the EGR back pressure variable transducer valve and open the EGR valve. The transducer valve closes under moderate levels of exhaust back pressure and intake vacuum, when sufficient engine speed and load are reached. Under these conditions, the action of the valve upon closing is to shut off the vent of ported vacuum, which is high enough to open the EGR valve when it is not being vented.