Exhaust Gas Recirculation: Description and Operation

This system is used to dilute the incoming air/fuel mixture with recirculated exhaust gases. Dilution of the incoming mixture lowers the peak flame temperatures and thus limits the formation of nitrous oxides (NOx).




DIESEL ENGINES

Exhaust gas recirculation is controlled by a single diaphragm, vacuum operated valve. Operating vacuum is supplied by an engine driven vacuum pump and regulated by a Vacuum Regulating Valve (VRV), mounted on the injection pump throttle lever. During normal operation, the EGR valve opening is controlled by vacuum signal strength through the VRV, as throttle angle increases, vacuum strength decreases. In addition, vacuum switching and control valves are used to limit system operation to specific engine operating conditions.



1985 2L Engines

Vacuum pump output on these engines is controlled by a Bimetal Vacuum Switching Valve (BVSV), Electronic Vacuum Regulating Valve (EVRV), Vacuum Control Valve (VCV) and High Altitude Compensation (HAC) valve. When coolant temperature is greater than 122°F and engine speed exceeds 1000 RPM under normal operating conditions, both BVSV and EVRV are open and exhaust gas is recirculated. Exhaust gas is not recirculated under any other operating conditions.