COMPUTERIZED ENGINE CONTROLS
960 models use a Motronic 1.8 injection and electronic ignition system. System has complete self-diagnostic capabilities.
System uses an Electronic Control Unit (ECU) that receives input from engine monitoring sensors. These sensors include camshaft sensor, coolant temperature sensor, oxygen sensor, knock sensor, mass airflow meter/sensor, timing pick-up and throttle switch. ECU uses these input signals to control air/fuel mixture for emission control, fuel economy and good driveability. Ignition and fuel controls are provided by a single ECU.
CONTROL UNITS
Electronic Control Units (ECUs) provide precise control of fuel and ignition. Each system has self-diagnostic capabilities.
960 models use a single ECU for ignition and fuel controls. ECU is located above and to the right of accelerator pedal.
Note. Components are grouped into 2 categories. The first category is INPUT DEVICES, which are components that control or produce voltage signals monitored by control unit. The second category is OUTPUT SIGNALS , which are components controlled by control unit.
INPUT DEVICES
Available input signals include
A/C Switch
Signals fuel injection ECU of A/C operation. This allows fuel injection ECU to control idle speed with idle valve.
Air Temperature Sensor
Information gathered from air temperature sensor is combined with information from pressure sensor to calculate intake air mass.
Engine Coolant Temperature Sensor
Engine Coolant Temperature (ECT) sensor is a negative temperature coefficient type, meaning its resistance lessens as temperature increases. Four cylinder sensor unit has 2 resistors. One resistor is connected to fuel injection ECU and the other resistor is connected to the ignition ECU.
Knock Sensor
Knock sensor detects knocking and sends signal to ECU. ECU is able to gradually retard ignition timing to each individual cylinder. If knocking does not stop, a signal is sent to ECU to enrich air/fuel mixture. Two knock sensors are equipped on 6-cylinder engines.
Mass Airflow Meter
This meter measures intake air mass. Measure sensor is a heated wire which is maintained at 250°F (120°C) warmer than intake air. ECU is able to calculate mass of intake air by measuring amount of current required to maintain wire temperature. When engine is turned off, any contaminants on wire is burned off by heating wire to greater than 1800°F (1000°C).
Mass Airflow 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)
Also known as a Lambda probe, this heated oxygen sensor generates an electrical signal proportional to air/fuel mixture. Motronic or fuel injection ECU uses this information to adjust amount of injected fuel.
Throttle Position (TP) Sensor
The TP sensor signals Motronic or ignition and fuel injection ECUs when throttle is fully closed or fully open.
OUTPUT SIGNALS
ECU processes information from input sensors and sends appropriate voltage control signals to control devices.
Note. For theory and operation of each output component, refer to system indicated after component.
CHECK ENGINE Light
See CHECK ENGINE LIGHT under SELF-DIAGNOSTIC SYSTEM.
EGR Solenoid Valve
See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS.
Fuel Injectors
See FUEL CONTROL under FUEL SYSTEM.
Fuel Pump
See FUEL DELIVERY under FUEL SYSTEM.
Idle Valve
See IDLE SPEED under FUEL SYSTEM.
Ignition Control Unit
See IGNITION SYSTEM .
Power Transistor & Ignition Coil
See ELECTRONIC IGNITION under IGNITION SYSTEM.
960 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. fuel pumps 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
ECU calculates base injection pulse width by processing signals from crankshaft position sensor (RPM), which is used to trigger timing of fuel injection. During normal driving conditions, injection duration is regulated in reference to mass air meter/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. Control unit 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. Fuel is injected into intake manifold close to each intake valve.
IDLE SPEED
Engine idle speed is controlled by ECU depending upon engine operating conditions. ECU 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 ECU determines idle speed by controlling amount of by-pass air.
ELECTRONIC IGNITION
Each cylinder is equipped with an individual ignition coil, eliminating the distributor. ECU computes instant at which each ignition coil must deliver its high voltage pulse. All 6 coils are controlled by 2 power units.
Ignition Timing Advance Control
Ignition timing is totally controlled by an ECU. Ignition timing is based on preprogrammed information and modified by inputs from engine sensors.
960 models have 2 knock sensors. Knock sensors are fitted to cylinder block to sense detonation inside cylinders. When detonation is detected, ECU 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 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.
EGR System
EGR system operates by returning some exhaust gases to engine to be mixed with air/fuel mixture. This exhaust gas, which is basically inert at this stage, lowers combustion temperature. Reducing combustion temperature reduces amount of oxides of nitrogen (NOx) released into atmosphere.
When engine coolant temperature is less than 115°F (45°C), solenoid receives no current and EGR system is inactive. With engine at operating temperature, solenoid receives current from relay and opens vacuum line to EGR valve. EGR valve is opened completely by negative pressure. Even the slightest throttle opening opens idle switch. Time relay cuts current to solenoid, disconnecting EGR system for about 5 seconds and avoiding HC and particle build-up during acceleration from idle.
EGR Electronic Vacuum Regulator Valve (EVRV)
EGR valve is supplied with a vacuum control signal from connection in lower section of the EVRV. Vacuum in intake manifold is supplied to upper connection. EVRV stabilizes signal from intake manifold and converts control module signal into a modified vacuum signal for controlling EGR valve.
Note. CHECK ENGINE light is also known as Malfunction Indicator Light (MIL).
CHECK ENGINE light is 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.