4-110 Engines

Fig. 51 EGR system operation. 1984-85 4-110/1.8L diesel engine:

The EGR system includes an intake manifold mounted EGR valve and stainlesssteel exhaust pickup tube, vacuum pump, vacuum switching valve, control module, and sensors that monitor engine and vehicle operating conditions. Operating vacuum for the EGR valve is provided by the vacuum pump through the vacuum switching valve which is controlled by the module. The module transmits ``ON-OFF'' electrical pulses to the vacuum switching valve according to engine RPM, injection pump lever angle, vehicle speed and coolant temperature. When the switching valve is energized, vacuum is supplied to the EGR valve, opening the valve; when the switching valve is off, the EGR valve closes.
The engine speed sensor, coolant sensor, control lever position sensor andvehicle speed sensor convert measured operating conditions into voltage signals which are transmitted to the control module. The module uses these signals to compute proper amounts of EGR, then controls operation of the vacuum switching valve accordingly. This allows the module to provide EGR only under conditions where it is needed to reduce NOx emissions and prevents recirculation under conditions where it will adversely affect driveability as shown in Fig. 51.