0010 - Function of the injection system O. Anti-jerk control (ARA) (note deviations for off-road vehicles) Engines 601, 602.91, 603.91

07.1-010 Function injection system

O. Anti-jerk control (ARA), engines 601.912/913, 602, 603 with manual transmission

General

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In order to reduce the tendency to jerking on vehicles with manual transmission, an electromagnetic actuator is attached to the injection pump governor which is able to reduce the injected volume.

The electromagnetic actuator is activated by an electronic control unit. On the engine 603 this function, as well as the previous ELR function, is assumed by the control unit which has taken the place of the previous ELR control unit.
The engine 602 with pneumatic idle speed increase is given a control unit only with ARA function.

Function

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The speed sensor (L3) registers the engine speed with 144 impulses/revolution, passing it on to the control unit (N8/1 or N8/2) in form of an AC voltage. Speed fluctuations or irregularities are recognized by the control unit (N8/1 or N8/2). By a temporary short reduction of the injection quantity the jerking tendency is reduced. In order to achieve an adequate reduction in the transition phase to coasting operation (zero delivery), a special damper serves to achieve a reduction of deceleration jerking.

Engine 602, 603

It is possible to influence the sensitivity of the control with a resistance trimming plug (if fitted) in order to reduce the jerking tendency in certain operating conditions.

Engine 602, 603

161 Electrical connection

162 O-ring

163 Stroke rod

2x ARA capsule

2y Shifting pin

2z Restoring spring

3d Reel sleeve

Y22/3 Electromagnetic actuator ARA

a Control travel 1.5-1.7 mm (capsule travel)
= control travel 2.25-2.55 mm

b Play to full-load stop 0.1-1.0 mm

Engine 601.912/913

1c Spring chamber cover

2 Governor

2d Control lever

2x Restoring spring

7h O-ring

8a Bolt

40 Steel washer

161 Seal

163 Vacuum element stroke rod

164 Magnetic core

169 Seal

a Reference size = 1.2 mm

Block diagram ARA/ELR engine 602, 603

Temperature sensor (ELR)

ARA-

ELR

Control unit
N8/1

ARA electromagnetic actuator

ELR electromagnetic actuator

Individual adjustment plug

TD signal

Injection pump

Speed sensor/engine (L3)

System diagnosis

Block diagram ARA engine 601.912/913

ARA-

Control unit

N8/2

ARA electromagnetic actuator

TD signal

Injection pump

Speed sensor/engine (L3)

System diagnosis

System diagnosis

With the self-testing program integrated in the control unit it is possible to test the ARA/ELR system.

Impulses can be called up via the test coupling (x92) which give concrete information on faults of a component.
However, only permanent faults can be displayed. Temporary faults cannot be registered and displayed by the control unit.
The number of impulses shows if and which component is defective or whether components in the control circuit are defective.

1) Control units with "RO1" are only able to identify short circuit faults.
Control units with "RO2" are also able to identify interruptions.

Production breakpoint: Control unit with "RO2"
May 1988

Impulse display	Component/Control circuit
1	All functions "in order"
2	Speed signal "fault"
3	Coolant temperature "fault"
5	Control circuit "ARA" "fault"
6	Control circuit "ELR" "fault"
7	Control circuit "ARA" output stage interruption
9	Control circuit "ARA" faulty