APC

APC System Components:

APC System Diagrams:

Locations of components

3 Earthing point, facia
At the left-hand front speaker socket

7 Earthing point
On the left-hand wheel housing

22A Fuse board
Behind the access panel in the glove compartment

29 Brake light switch
At the brake pedal

146 Amplifier for the electronic ignition system
On the left-hand wheel housing

147 Ignition pulse amplifier
In the electrical distribution box behind the glove compartment

177 Control unit for the APC system
1987: under the facia, to the left of the steering column (behind the knee shield)
1988: under the left-hand front seat

178 Knock sensor
On the engine, under 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)

187 Vacuum pump for the Cruise Control
On the right-hand side of the engine compartment

228A Filament monitor
In the electrical distribution box behind the glove compartment

230 Distribution terminal +30
In the electrical distribution box behind the glove compartment

231 Distribution terminal +54
In the electrical distribution box behind the glove compartment

233 Vacuum switch
Under the facia, to the left of the steering column (behind the knee shield)

341 Earthing point
On the left-hand front seat member

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.

The system includes:

control unit 177, which receives signals from various transmitters, processes the signals and then adjusts the charging air pressure by means of solenoid valve 179.

knock sensor 178, which senses any knocking in the engine

pressure transmitter 180, which senses the pressure in the intake pipe upstream of the throttle.

The supply to the APC system (the control unit) is taken across fuse 5 in the electrical distribution box when the ignition switch is set to the drive position.

Control pulses are received from ignition pulse amplifier 147 (1987)/ignition system amplifier 146 (1988). In addition, brake light switch 29 closes when the car is braked, causing the control unit to reduce the turbocharger boost pressure to the basic setting.

The signals from the transmitters and from the ignition system are fed continuously into the control unit. On the basis of the signals received, the unit then controls the solenoid valve and thus the charging air pressure from the turbocharger. Since the boost pressure is continually 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.

Turbo models with Cruise Control are equipped with vacuum switch 233, which actuates the vacuum pump via a vacuum hose. When the switch opens, the control unit reduces the boost pressure to the basic setting.

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 open-circuit, etc.

Resistance reading for pressure transmitter (measured at atmospheric pressure): 5-13 ohms