APC System (Automatic Boost Control)
APC-systemOperation
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.
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.