General Information

The EDS control unit processes the following functions:

- Electronic Idle Speed Control (ELR)
- Exhaust Gas Recirculation (EGR)
- Boost Pressure Control
- System Diagnostics


Operation:

Module Box:

The control unit processes the incoming signals and delivers a milliamp current to the two vacuum transducers (Y31/1, Y31/4) and to the electromagnetic actuator on the injection pump. The entire system can be tested with an impulse counter, i.e. the malfunction memory can be read by means of an output signal to the test connection (X11/4). Testing and Inspection

NOTE: All system components are described herein.


Atmospheric Pressure Sensor (Integrated into Control Unit)
Depending on altitude or atmospheric pressure, the atmospheric pressure sensor influences EGR volume. The atmospheric pressure sensor sends the control unit a voltage signal which is proportionate to the atmospheric pressure (i.e. low voltage at low pressure). In other words, the control unit determines EGR volume according to the relative atmospheric pressure via a reduction in vacuum transducer current.


Test Connection for Diagnosis (X11/4)




The impulse readout for diagnosis can be picked up at socket 4 of the 38-pole test connection.


Air flow sensor (B2/1)
Intake Air Temperature Sensor (B2/1a)




Located in the air flow between the air filter and the turbocharger.





Acting against a return spring, intake air opens the air flow sensor plate to a specific angle. The position of the plate is measured by a potentiometer which converts the position into a voltage signal.

The intake air temperature is read by the temperature sensor (B2/1a) in the air flow sensor.


Vacuum Transducer (Y31/1, Y31/4)




Y31/1 EGR Valve vacuum transducer
Y31/4 Boost pressure control vacuum transducer

Respective to operating conditions, the vacuum transducers receive a control current from the control unit. The vacuum transducers then deliver a corresponding amount of vacuum for the EGR valve or the boost pressure control valve.


EGR Switchover valve (Y27), A/C Compressor Cut-Out/EGR Microswitch (S27/6)








The EGR switchover valve (Y27) is activated by the control linkage microswitch (S27/6) 10° before full load, thereby closing the EGR valve.


Boost Pressure Cut-Out Switchover Valve (Y31/6)




Should a malfunction occur in the boost pressure control circuit, the boost pressure cut-out switchover valve (Y31/6) vents the boost pressure control valve.
As a result, boost pressure cannot be built up and injected fuel quantity is reduced.


Starter Ring Gear Speed Sensor (L3)




Determines engine speed via the starter ring gear (144 impulses per revolution) and sends it in the form of a AC voltage signal to the control unit.


Pressure (P2) Sensor (B5/1)




Located on the left, ahead of the firewall, the pressure sensor reads the pressure (P2) and converts it into a voltage signal which is used by the EDS control unit as an input signal.





Pabs Absolute pressure in mbar, reference at 5 V supply voltage.


EGR Valve (60)




60 EGR Valve
61 Corrugated tube
135 Mixture tube

The EGR valve is mounted laterally on the mixture tube which is bolted to the cylinder head. The connection to the exhaust manifold is made by means of corrugated tube. The EGR valve is activated by a controlled vacuum from the vacuum transducer (Y31/1).





A Previous version
B New version
a Vent shaft
b Valve seal

To reduce noise, the EGR valve has a smaller vent shaft (a) and a contoured valve seat (b). The pipe connection for the vacuum line is tulip shaped.


Coolant Temperature Sensor (EDS)(B11/4)




The coolant temperature sensor sends a signal relevant to coolant temperature to the EDS control unit.