TURBOCHARGERS
Turbo models use a water-cooled Turbocharger (TC), mounted directly to exhaust manifold, with a wastegate assembly attached to rear of turbine housing. Turbocharger consists of a turbine/compressor assembly, oil supply system and wastegate. Other components include impellers, impeller shaft, bearings and impeller housings.
The Electronic Control Module (ECM) monitors boost pressure continuously using information supplied by Mass Airflow (MAF) sensor. If boost pressure exceeds permissible level, ECM will close TC control valve so that boost pressure is limited to basic value. If pressure continues to rise despite adjustment, ECM will interrupt fuel supply by keeping injectors closed.
If boost pressure exceeds safe limits, engine damage may result. The wastegate opens when exhaust pressure exceeds a predetermined limit and allows exhaust gases to by-pass compressor. Turbocharger operation requires a large quantity of clean oil to prevent bearing failure. Engine oil pressure provides constant lubrication to system.
At idle and light throttle, turbo engine operates like a standard engine. When more power is required, exhaust gases from exhaust manifold enter turbocharger turbine housing and flow through turbine blades. Exhaust flow and turbine speed increase as throttle opens and RPM increases. Impeller turns with turbine and forces air into compressor housing and intake manifold. As impeller and turbine speed increases, boost pressure also increases.
COMPUTERIZED ENGINE CONTROLS
All models use a similar Motronic 4.4 fuel injection and electronic ignition system with complete self-diagnostic capabilities. Systems uses a single Electronic Control Module (ECM) that receives input from engine monitoring sensors. These sensors include Camshaft Position (CMP) sensor, Engine Coolant Temperature (ECT) sensor, Heated Oxygen (HO2S) sensor, Knock Sensor (KS), Mass Airflow (MAF) sensor, A/C pressure sensor, acceleration sensor, RPM sensor, timing pick-up, and Throttle Position (TP) sensor. ECM uses these input signals to control air/fuel mixture for emission control, fuel economy and good driveability.
CONTROL MODULE
Electronic Control Module (ECM) provides precise control of fuel, ignition and turbo operation (if equipped). Each system has self-diagnostic capabilities. All models use a single ECM for ignition and fuel controls. On C70, S70 and V70, ECM is located in right front of engine compartment. On S90 and V90, ECM is located under left side of instrument panel, on "A" pillar.
Note. Components are grouped into 2 categories. The first category is INPUT DEVICES, which control or produce voltage signals monitored by ECM called input signals. The second category is OUTPUT SIGNALS, which are components controlled by ECM.
INPUT DEVICES
All vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine input usage on a specific model, see WIRING DIAGRAMS article. Available input signals include
Acceleration/Accelerometer Sensor
On C70, S70 and V70, acceleration/accelerometer sensor is mounted under the right front of vehicle, on the subframe. On S90 and V90, acceleration/accelerometer is mounted on brace in left rear engine compartment. Sensor consists of a piezoelectric vibration pick-up that detects vertical acceleration of vehicle, for example driving on a bumpy road. ECM uses this sensor signal to determine if irregularities in crankshaft rotation are due to cylinder misfiring or due to driving on an uneven road surface.
A/C Pressure Sensor
Signals ECM of A/C operation. This allows ECM to control idle speed.
Camshaft Position (CMP) Sensor
ECM uses CMP sensor signal to determine in which cylinder ignition is required and, if knock is detected, which cylinder is knocking.
Engine Coolant Temperature (ECT) Sensor
ECT sensor is a negative temperature coefficient type, meaning its resistance lessens as temperature increases.
Engine Speed (RPM) Sensor
Edge of flywheel/carrier plate has a series of holes along its edge. As it passes RPM sensor, each hole induces a voltage in coil.
Knock Sensor (KS)
Knock sensor detects knocking and sends signal to ECM. ECM is able to gradually retard ignition timing to each individual cylinder. If knocking does not stop, a signal is sent to ECM to enrich air/fuel mixture. Two knock sensors are equipped on 6-cylinder engines.
Mass Airflow (MAF) Sensor
This sensor uses a hot film, rather than a heated wire to measure intake air mass. Since working temperature is high at 338°F (170°C), and flow and temperature-sensitive resistances are mounted on side of hot film, a burn-off function is not required.
Heated Oxygen Sensor (HO2S)
Heated oxygen sensor generates an electrical signal proportional to air/fuel mixture. ECM uses this information to adjust amount of injected fuel.
Throttle Position (TP) Sensor
TP sensor signals ECM when throttle is fully closed or fully open.
OUTPUT SIGNALS
ECM processes information from input sensors and sends appropriate voltage control signals to control devices.
Note. Vehicles are equipped with different combinations of computer-controlled components. Not all components listed below are used on every vehicle. For theory and operation of each output component, refer to system indicated after component.
A/C Clutch
See appropriate article in A/C-HEATER SYSTEM - AUTOMATIC in AIR CONDITIONING & HEAT section.
Malfunction Indicator Light (MIL)
See MALFUNCTION INDICATOR LIGHT (MIL) under SELF-DIAGNOSTIC SYSTEM.
Cold Start Valve
See FUEL CONTROL under FUEL SYSTEM.
Fuel Injectors
See FUEL CONTROL under FUEL SYSTEM.
Fuel Pump
See FUEL DELIVERY under FUEL SYSTEM.
Idle Valve
See IDLE SPEED under FUEL SYSTEM.
Power Transistor & Ignition Coil
See ELECTRONIC IGNITION under IGNITION SYSTEM.
C70, S70 and V90 models are equipped with an in-tank fuel pump. S90 and V90 models are equipped with 2 fuel pumps. These are a primary low pressure pump, located in fuel tank, and a high pressure in-line pump. On all models, fuel pump(s) are equipped with check valves to hold fuel pressure in system when ignition is off. Fuel from main pump is sent through an in-line fuel filter. Fuel is then sent to fuel pressure regulator where pressure is maintained at a constant pressure in relationship to manifold pressure. Excess fuel returns to fuel tank via a return line.
Fuel Pressure Regulator
Pressure regulator is a sealed unit which is divided by a diaphragm into 2 chambers (fuel and spring chambers). Fuel chamber receives fuel through inlet side from injector fuel rail. Spring chamber is connected to intake manifold vacuum. At idle, intake manifold vacuum is high. Diaphragm is pulled back by intake manifold vacuum. Any excessive fuel is returned to fuel tank. As throttle is depressed, intake manifold vacuum decreases. Regulator spring overcomes manifold vacuum, increasing fuel pressure.
FUEL CONTROL
ECM calculates base injection pulse width by processing signals from various engine sensors. Information from RPM sensor at flywheel is used to trigger timing of fuel injection. During normal driving conditions, injection duration is regulated in reference to MAF sensor, engine speed, oxygen content of exhaust gases and coolant temperature. Under full throttle conditions, a richer fuel mixture is provided for increased power and to reduce combustion heat in engine and catalytic converter.
Each injector incorporates a solenoid, plunger and needle valve which opens and closes an orifice. ECM supplies current through auxiliary relay for a predetermined period, opening all injectors simultaneously to inject atomized fuel. Injection takes place twice per revolution while starter motor is running and once per revolution under normal driving conditions.
IDLE SPEED
Engine idle speed is controlled by ECM depending upon engine operating conditions. ECM senses engine operating conditions and determines best idle speed. Idle speed is controlled by varying air passage inside idle valve.
Idle valve uses a solenoid or motor to control by-pass air. Signal from ECM determines idle speed by controlling amount of by-pass air.
ELECTRONIC IGNITION
Models use a flywheel sensing permanent magnet generator to determine crankshaft position and engine speed.
On C70, S70 and V70, ECM computes correct timing of each ignition pulse in response to signals from RPM sensor, Camshaft Position (CMP) sensor, Mass Airflow (MAF) sensor, Engine Coolant Temperature (ECT) sensor, Throttle Position (TP) sensor, Knock Sensors (KS) and Transmission Control Module (TCM).
On S90 and V90, each cylinder is equipped with an individual ignition coil, eliminating the distributor. ECM computes when each ignition coil must deliver its voltage pulse. All 6 coils are controlled by 2 Ignition Discharge Modules (IDM).
Ignition Timing Advance Control
Ignition timing is controlled by ECM. Ignition timing is based on preprogrammed information and modified by inputs from engine sensors.
Knock Sensor
Models have 2 knock sensors. Knock sensors are fitted to cylinder block to sense detonation inside cylinders. When detonation is detected, ECM retards ignition timing in each cylinder individually until knocking stops.
FUEL EVAPORATIVE SYSTEM (EVAP)
Evaporative emissions system is designed to prevent fuel vapor from entering atmosphere. Fuel system is completely sealed and vented only through a carbon canister. System consists of pressure/vacuum relief fuel filler cap, rollover valve, charcoal canister, purge valve and various connecting hoses. Fuel pressure/vacuum relief filler cap allows excessive tank pressure to vent. It also allows air into fuel tank if vacuum should become excessive due to a malfunction in fuel evaporation system. Fuel tank vapor is vented by a line through rollover valve to charcoal canister. Rollover valve is located in vent line close to fuel tank. Valve is designed to prevent fuel spillage if vehicle rolls over. Valve is open until vehicle is at a 45-degree angle or more from horizontal position.
Canister Purge (CP) Valve
Charcoal canister is filled with activated charcoal. Fuel vapor from tank is absorbed by charcoal when engine is not running. When engine is running faster than idle, canister purge valve opens and fuel vapor is drawn into engine and burned.
All models are equipped with a CHECK ENGINE MIL located on instrument panel. Light will illuminate when ignition switch is turned to ON position (bulb check) or when emission-related systems are malfunctioning during normal engine operation.