INTRODUCTION
This article covers basic description and operation of engine performance-related systems and components. Read this article before diagnosing vehicles or systems with which you are not completely familiar.
TURBOCHARGERS
Turbo models use a water-cooled turbocharger, 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 safety valve of system is a pressure actuated wastegate that prevents excessive intake boost pressure. The wastegate is controlled by the turbo control valve. This 3-port solenoid valve monitors boost pressure and prevents turbo lag. The control valve is activated by turbo control unit, which receives signals from throttle position sensor, fuel injection ECU and turbo pressure sensor.
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's 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
Models with 4-cylinder engines use a Bosch LH-Jetronic multi-point fuel injection system with EZ116K electronic ignition system or Regina (Bendix) multi-point fuel injection system with Rex-1 electronic ignition system. Both systems have self-diagnostic capabilities.
All 6-cylinder models use a Motronic 1.8 injection and electronic ignition system. System has complete self-diagnostic capabilities.
All systems use an Electronic Control Unit (ECU) that receives input from engine monitoring sensors. These sensors include camshaft sensor (Motronic), coolant temperature sensor, air temperature sensor (Regina), pressure sensor (Regina), oxygen sensor, knock sensor (turbo and Motronic), mass airflow meter (Bosch and Motronic), timing pick-up (Motronic) and throttle switch. ECU uses these input signals to control air/fuel mixture for emission control, fuel economy and good driveability. On 4-cylinder models, ignition control is provided by a separate ignition ECU. On 6-cylinder models, ignition and fuel controls are provided by a single ECU.
CONTROL UNITS
4-cylinder models use separate Electronic Control Units (ECUs) for fuel injection and ignition control. Turbo models also use a turbo ECU. 6-cylinder models use a single ECU for ignition and fuel controls. Control unit(s) provide precise control of fuel, ignition and turbo operation. Each system has self-diagnostic capabilities and use same diagnostic unit for trouble code output.
On 4-cylinder models, fuel injection control unit is located behind right front kick panel. Ignition control unit is located behind left side of instrument panel, near accelerator pedal. Turbo control unit is located behind left kick panel. On 6-cylinder models, ECU is located above and 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
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
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.
Coolant Temperature Sensor
Coolant temperature 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.
Detonation (Knock) Sensor (Motronic & Regina)
Knock sensor detects knocking and sends signal to Motronic or ignition ECU. ECU is able to gradually retard ignition timing to each individual cylinder. If knocking does not stop, a signal is sent to Motronic or fuel injection ECU to enrich air/fuel mixture. 6-cylinder engines are equipped with 2 knock sensors.
Ignition Control Unit (4-Cylinder)
Ignition ECU serves as an input device for fuel injection calculation. Ignition ECU provides information on engine speed, crankshaft position, knocking, etc.
Intake Air Temperature Sensor (Regina)
Air in intake manifold passes through a hole in sensor and affects a probe. Resistance of probe reduces with increasing temperature. With addition of signals from pressure sensor and temperature sensor for intake air, control unit can calculate volume of air inducted into engine.
Manifold Absolute Pressure Sensor (Regina)
Also called a pressure sensor, sensor measures both atmospheric and manifold absolute pressure. ECU calculates intake air mass from these inputs.
Mass Airflow Meter (LH-Jetronic)
This meter measures intake air mass. Measure sensor is a heated wire which is maintained at 250°F (120°C) warmer than intake air. Motronic or fuel injection 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).
Oxygen Sensor
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 Switch
This switch signals Motronic or ignition and fuel injection ECUs when throttle is fully closed or fully open.
Turbo Control Unit
Unit monitors turbo system and provides information for fuel injection control unit.
OUTPUT SIGNALS
ECU 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 MISCELLANEOUS CONTROLS .
CHECK ENGINE Light
See CHECK ENGINE LIGHT under SELF-DIAGNOSTIC SYSTEM.
Cold Start Valve
See FUEL CONTROL under FUEL SYSTEM.
Cooling Fan Motor
See MISCELLANEOUS CONTROLS .
EGR Control 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 .
Oxygen Sensor Heater Control
See FUEL CONTROL under FUEL SYSTEM.
Power Transistor & Ignition Coil
See ELECTRONIC IGNITION under IGNITION SYSTEM.
See TURBOCHARGERS under AIR INDUCTION SYSTEM.
All 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. Both 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 through 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 various engine sensors. Information from crankshaft position sensor (RPM) is used to trigger timing of fuel injection. During normal driving conditions, injection duration is regulated in reference to mass air meter, 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 inlet valve.
Cold Start Valve (4-Cylinder)
Since fuel condenses on engine surfaces under extremely cold conditions, cold start valve compensates for this condition. Located further upstream of the engine than injectors, valve supplies fuel in more gaseous form than injectors. Operated directly by the ECU, rather than by a thermal timer, valve opens at about 5°F (-15°C) and stays open until an engine speed of about 900 RPM. Valve remains closed at engine speeds greater than 900 RPM.
Oxygen (O2) Sensor Heater Control
O2 sensor operates only within a certain temperature range, approximately 545-1530°F (285-850°C). It is electrically heated to enable it to reach operating temperature quickly. When ignition is turned on, current is sent to a Positive Temperature Coefficient (PTC) resistor whose resistance increases with rising temperature. Because of this, O2 sensor quickly reaches correct operating temperature, even at low exhaust gas temperatures.
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
On 4-cylinder engines, electronic ignition ECU controls primary windings of ignition coil using signals from fuel injection ECU based on crankshaft position, engine speed and vehicle speed. Turbo models use a Hall Effect sensor, located in distributor, to determine crankshaft position and engine speed. Non-turbo models use a flywheel sensing permanent magnet generator to determine crankshaft position and engine speed.
On 6-cylinder engines, 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 six coils are controlled by 2 power units.
Ignition Coil (4-Cylinder EZ116K)
System uses a conventional ignition coil.
Power Transistor & Ignition Coil (4-Cylinder Rex-1)
Ignition coil receives battery voltage through fuse panel and is grounded through power stage (power transistor). When ECU is signaled of proper crankshaft position, power stage removes ground from coil, firing plug.
Power Units & Ignition Coils (6-Cylinder)
Ignition coils are mounted directly on spark plugs. Two power units (mounted on intake manifold) are used to control coils. Front power unit is connected to cylinders No. 1, 3 and 5. Rear power unit is mounted to cylindersNo. 2, 4 and 6. Each power unit uses 3 power stages, each connected to an individual coil.
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.
Detonation (Knock) Sensor
4-cylinder turbo engines have one knock sensor. 6-cylinder engines have 2 knock sensors. Knock sensor is fitted to cylinder block to sense detonation inside cylinders. When detonation is detected, ECU retards ignition timing in each cylinder individually until knocking stops. If knocking continues, ignition control unit signals turbo control unit to reduce boost pressure in stages.
EVAPORATIVE EMISSIONS
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.
Turbo Models
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.
EGR Control Solenoid Valve (4-Cylinder)
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 least 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.
SELF-DIAGNOSTIC SYSTEM
All models are equipped with self-diagnostic systems. A CHECK ENGINE light glows to signal driver of a system malfunction. Fault codes are retrieved through the diagnostic unit, located in left rear corner of engine compartment on 4-cylinder models or in right rear corner of engine compartment on 6-cylinder models. The diagnostic unit is equipped with an LED indicator, activation button and function select cable.
All models are equipped with a CHECK ENGINE light located on instrument panel. Light will glow when ignition switch is turned to ON position (bulb check) and when emission-related systems are malfunctioning during normal engine operation.
Motronic ECU controls operation of A/C clutch by means of a relay in Electronic Climate Control (ECC) power unit.
Radiator fan is operated by a relay either in response to engine temperature signal supplied by Motronic control unit or directly by pressure switches mounted in A/C high pressure circuit.
See also:
• MISCELLANEOUS CONTROLS
• FUEL CONTROL
• IDLE SPEED
• ELECTRONIC IGNITION
• TURBOCHARGERS