EGR System: Operation: 190D
The EDS control unit supplies signal to the vacuum control valve, which controls vacuum supply to EGR valve. Vacuum is supplied by a vacuum pump. The EDS receives input signals from sensors measuring engine conditions. These input sensors include engine speed, coolant temperature, fuel injection rack position (load), intake air temperature, intake air flow, and barometric pressure. For additional information on testing and diagnosing EDS input sensors, see BOSCH DIESEL FUEL INJECTION article in the FUEL SYSTEMS section.
The vacuum control valve outlet controls operating vacuum to EGR valve by using a vacuum amplifier. The vacuum amplifier regulates modulated vacuum according to load condition (accelerator position). The vacuum control flap is vacuum actuated and activated by the EDS through a switchover valve. Full vacuum is then applied to actuator, closing the vacuum control flap.
With vacuum control flap closed, vacuum is created in the intake manifold. This causes more exhaust gas to be recirculated. Engine RPM and vehicle speed are monitored by the RPM sensor and processed by the EDS.
The vacuum control flap and EGR valve are opened or closed by switchover valves, depending on operating conditions of the engine. During EGR operation, a portion of the exhaust gas is diverted to the intake manifold by EGR valve.
The EGR valve is operational under the following conditions:
- Coolant temperature must be between 77°F (25°C)-206°F (97°C).
- Engine speed 970-3020 RPM.
- Vehicle speed less than 54 MPH (87 Km/h).
- Accelerator pedal less than full throttle (a micro-switch shuts off the EGR system when full-throttle is reached).