APC System (Automatic Boost Control)

APC-System Diagrams:

APC-System Components:

Locations of components

5 Ignition coil
On the cross-member above the radiator

7 Earthing point
On the radiator cross-member

9 Earthing point
In the luggage compartment

22 Fuse box
In the electrical distribution box in the engine compartment, on the left-hand wheel housing

29 Brake light switch
At the brake pedal

60 Single-pole connector
In the engine compartment, behind the expansion tank

73 Timing service instrument socket (TSI socket)
In the electrical distribution box in the engine compartment, on the left-hand wheel housing

147 Ignition pulse amplifier
In the electrical distribution box in the engine compartment, on the left-hand wheel housing

152A 29-pole white connector
152C 29-pole black connector
In the electrical distribution box in the engine compartment on the left-hand wheel housing. The connector is accessible from the interior of the car.

177 Control unit for the APC system
1984 and 1985 models: under the back seat, on the left-hand side
1986 models: in the engine compartment, forward of the left-hand wheel housing

178 Knocking sensor
On the engine, below the intake manifold

179 Solenoid valve
On the radiator fan casing

180 Pressure transmitter
Under the facia, to the left of the steering column (behind the knee shield)

233 Vacuum switch
In the engine compartment, on the left-hand wheel housing

Operation
The engine is equipped with an Automatic Performance Control (APC) system, which enables the engine to adjust itself automatically to the grade of fuel supplied to it at any particular time.

1984 and 1985 models
The APC system is controlled by control unit 177, which is supplied (+54) from fuse 10 via the 29-pole white connector 152A.The unit receives signals from several sensors, processes the signals and then controls the charging pressure of the turbocharger via solenoid valve 179.

The system receives information from the following sensors:

Knocking sensor 178, which senses any knocking in the engine

Pressure transmitter which senses the pressure in the intake pipe upstream of the butterfly valve.

The electrical signals from the sensors and from ignition coil 5 are fed continuously into the control unit. On the basis of the electrical signals received, the unit then controls the solenoid valve and thus the boost pressure from the turbocharger. Since the boost pressure is continuously adjusted to the octane rating of the fuel and the running conditions of the engine, it has proved unnecessary to provide the adjustment margins that must normally be allowed to avoid damage to the engine. As a result, maximum energy can be extracted from the fuel used on any particular occasion.

Cars with the Turbo 16 engine and Cruise Control are equipped with vacuum switch 233, which is actuated by the vacuum pump via a vacuum hose. When the contacts open, the control unit reduces the boost pressure to the basic value.

1986 models
The control unit has been replaced on the 1986 models (new pin numbers).

The operation is the same as on 1984 and 1985 models, except that the control pulses are supplied from ignition pulse amplifier 147 instead of from the ignition coil In addition, brake light switch 29 applies a signal when the car is braked, which causes the control unit to reduce the boost pressure to the basic value.

Fault-tracing hints
The following items must always be taken into account before fault-tracing is started on the APC system:

1. Disconnect the connector from the control unit.

2. Disconnect the connector from the component which is suspected to be faulty.

3. Use an ohmmeter to check the wiring for any open circuits, etc.