Function of the Components
Component operationEDS control unit (N39)
The control unit processes the incoming signals and delivers a milliamp current to the two vacuum transducers, to the electromagnetic actuator on the injection pump, and the boost pressure control and pressure control flap switchover valves. The entire system can be tested with an impulse counter i.e. the malfunction memory can be read by means of the test connection (X11/4, socket 4).
Atmospheric pressure sensor (Integrated into control unit)
Depending on altitude or atmospheric pressure, the atmospheric pressure sensor influences EGR volume and boost pressure. The atmospheric pressure sensor sends the control unit a decreasing voltage signal at decreasing air pressures (increasing altitudes). The EGR and P2 reference map values are adapted according to a pressure dependent characteristic.
Test connection for diagnosis (X11/4)
The impulse readout for diagnosis can be picked up at this test connection.
Air flow sensor (B2/1)
Intake air temperature sensor (B21/a)
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 transducers (Y31/1, Y31/5)
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 electric switchover valves.
Y31/1 EGR valve vacuum transducer
Y31/5 Boost pressure control/pressure control valve vacuum transducer (not visible, located under air filter)
EGR switchover valve Y27), EGR microswitch (S27/3)
The EGR switchover valve (Y27) is activated by the control linkage microswitch (S27/3) 100 before full load, thereby closing the EGR valve.
Electric switchover valves (Y27/4, Y27/5)
Depending on operating conditions, the electric switchover valves receive a control current from the control unit and vacuum from the vacuum transducer (Y31/5). They convey the control unit command as a pneumatic signal to the boost pressure control valve and pressure control flap.
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 sensor (B5/1)
Located on the right, behind 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.
EGR valve (60)
The EGR valve, together with the mixture tube, is bolted laterally to the cylinder head. It is connected to the exhaust manifold, the intake manifold crossover pipe and to a corrugated tube. Controlled vacuum from the switchover valve (Y27) and vacuum transducer (Y31/1) is applied to the EGR valve to open the valve.
A Exhaust to the intake manifold
B Exhaust from the exhaust manifold
a Vacuum connection
b Spring
c Diaphragm
d Valve
Coolant temperature sensor (B11/4)
Coolant temperature is determined by the coolant temperature sensor (B11/4) which is controlled by the EDS control unit. The temperature sensor resistance changes according to coolant temperature.
Housing (94a) with pressure control flap (99) and vacuum actuator (100)
A pneumatically operated pressure control flap, located in a housing on the intake manifold, adjusts boost pressure in the intake manifold. The pressure control flap closes the fresh air intake during EGR operation. A minimal opening (arrows) between the pressure control flap and the housing remains. The vacuum actuator (100) is activated by the pressure control flap switchover valve (Y27/5) and vacuum transducer (Y31/5).
