Diesel Engines: Notes

The EDS control unit supplies a signal to the vacuum control valve, which controls the vacuum supply to the 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 appropriate BOSCH DIESEL FUEL INJECTION article in the FUEL SYSTEMS section.

The vacuum control valve outlet controls the operating vacuum to the EGR valve by using a vacuum amplifier. The vacuum amplifier regulates the 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 the actuator, closing the vacuum control flap.

With the vacuum control flap closed, a 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 the 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 the EGR valve.