INTRODUCTION
This article covers the basic description and operation of engine performance-related systems and components. Read this article before diagnosing vehicles or systems you are not completely familiar with.
TURBOCHARGERS
Turbocharger consists of a turbine/compressor assembly, oil supply system and wastegate. Other components include impeller, impeller shaft, bearings and impeller housing. Turbocharger assembly is mounted directly to exhaust manifold, with wastegate assembly attached to rear of turbine housing.
Air intake charge is cooled by an intercooler. Coolant to water-cooled turbo flows from water hose (at bottom of thermostat housing) through water pipe, to turbocharger. After cooling turbocharger, coolant is returned through water inlet pipe.
Engine oil provides constant lubrication for system. Oil for turbocharger lubrication flows from cylinder head oil passage through oil pipe, and is returned to oil pan through oil return pipe.
At idle and light throttle, turbocharged engine operates like 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 increases as throttle opens and RPM increases. The impeller turns with turbine, and forces air into compressor housing and intake manifold. As impeller and turbine speed increases, boost pressure also increases.
The safety valve of the system is a pressure-actuated wastegate which prevents excessive intake boost pressure. If boost pressure exceeds safe limit, engine damage may result. When exhaust pressure exceeds a predetermined limit, the wastegate opens and allows exhaust gases to by-pass compressor, limiting boost pressure.
TURBOCHARGER PRESSURE CONTROL
Turbocharger pressure control is used to control turbocharger pressure by regulating the activating pressure of wastegate actuator.
TURBO METER
Turbo meter displays turbocharger pressure. When ignition switch is in the ON position, turbo meter indicator will be on "0". When engine is started, indicator will move from "0" to the "-" side. As boost pressure increases, indicator will move to the "+" side.
CONTROL UNIT LOCATION & OPERATION
Computerized engine control system monitors and controls emission, fuel and ignition system components. Input sensors supply information to engine Electronic Control Unit (ECU). The ECU (also known as MPI control unit) processes information from input sensors and sends output signals to control devices. See INPUT DEVICES and OUTPUT SIGNALS in this article.
Electronic Control Unit (ECU) is located under center of dash, behind center console. (Scheme 1) ECU receives input voltage signals from a variety of input devices. The ECU compares each of the voltage input signals to a preset parameter which is programmed into the ECU. The ECU instantly analyzes each of the input voltage signals and adjusts output voltage signals accordingly. This allows for lower emissions while maintaining fuel economy and driveability.
Scheme 1
INPUT DEVICES
Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the control unit. The second category covers OUTPUT SIGNALS, which are components controlled by the ECU.
Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input device used on a specific model, see WIRING DIAGRAMS article. The available input signals are as follows.
A/C CONTROL UNIT
A/C control unit is located above A/C-heater unit. (Scheme 2) A/C control unit prevents idle speed from dropping due to A/C compressor load, ensuring a stable idle speed. A/C control unit sends A/C system on-off signal to ECU. When A/C is turned on and ECU receives on signal from A/C control unit, ECU commands idle speed control servo to increase idle speed to a preset RPM.
Scheme 2
AIRFLOW SENSOR
Airflow sensor is located inside air cleaner assembly. Intake air temperature sensor and barometric pressure sensor are built into airflow sensor. The airflow sensor senses intake air volume and sends a signal to the Electronic Control Unit (ECU). Using airflow sensor and engine RPM signal, ECU makes computations to determine basic fuel injection timing.
Air temperature sensor sends signal to ECU to adjust and correct amount of fuel to be injected. Barometric pressure sensor senses barometric pressure and converts it to electrical voltage signals. Voltage signals are sent to ECU to calculate vehicle altitude, and correct fuel injection quantity and timing for optimum air/fuel ratio. This improves driveability at high altitudes.
COOLANT TEMPERATURE SENSOR (CTS)
The CTS is located on thermostat housing. CTS monitors coolant temperature and sends a voltage signal to ECU. CTS has a built-in thermistor, whose resistance varies according to coolant temperature. The ECU determines engine temperature based on output voltage of CTS to provide optimum mixture enrichment when engine is cold.
CRANK ANGLE SENSOR
On all 2.0L engines, crank angle sensor is located on rear side of cylinder head, coupled to intake camshaft. On 1.8L engine, crank angle sensor is located inside distributor. Crank angle sensor provides ECU with engine speed and crankshaft angle position. Crank angle sensor consists of a disc and sensor unit.
The metal disc has 4 slits located 90 degrees apart, and 2 slits (1 slit on 1.8L) located inward of the 4 slits, 180 degrees apart. On all 2.0L engines, the 2 inner slits are used by the top dead-center sensor to detect top dead center of No. 1 and No. 4 cylinders. On 1.8L engines, the inner slit is used by the top dead-center sensor to detect top dead center of No. 1 cylinder. On all engines, the outer 4 slits are used by the crank angle sensor to detect crank angle.
On all 2.0L engines, the disc is positioned on the crank angle sensor shaft and is turned with sensor shaft by intake camshaft. On 1.8L, the disc is fixed to distributor shaft and rotates as distributor turns. On all engines, crank angle sensor unit has 2 LEDs and 2 photo diodes to detect crank angle sensor slits and top dead-center sensor slits. The disc rotates between the LEDs and photo diodes. Each time a slit comes between LED and photo diode pair, light emitted by LED passes through the slit to photo diode.
DETONATION SENSOR (2.0L TURBO MODELS)
Detonation sensor is located on left side of cylinder block (firewall side). Detonation sensor detects cylinder block vibrations caused by knocking and sends signal to ECU. The ECU retards ignition timing according to strength of knocking.
EXHAUST GAS TEMPERATURE SENSOR (CALIFORNIA MODELS)
See EMISSION SYSTEMS in this article.
ENGINE IGNITION SIGNAL (2.0L & 2.0L TURBO)
Ignition coil senses engine ignition signal. If an abnormal condition, such as ignition signal is not generated, occurs during engine operation, ECU will detect fault and set Fault Code 44 in memory. CHECK ENGINE light will also illuminate.
FUEL PUMP RELAY (CONTROL RELAY)
Fuel pump relay is located on right side of center console. (Scheme 3) Relay senses when power is supplied to fuel pump. If power to fuel pump does not occur during engine cranking or driving, ECU detects fault and set Fault Code 42 in memory. CHECK ENGINE light will also illuminate. Fuel pump relay is a multi-purpose relay. See FUEL PUMP RELAY under OUTPUT SIGNALS in this article.
Scheme 3
IDLE POSITION SWITCH
On all 2.0L engines, idle position switch is located on throttle body. On 1.8L engines, idle position switch is part of idle speed control servo, located on throttle body. (Scheme 7) Idle position switch is a contact-type switch, which detects operation of accelerator pedal and sends signal to ECU. Idle position switch also serves as a throttle stop screw.
IGNITION SWITCH
The Ignition switch sends signal to ECU indicating whether switch is on, off, or cranking (ST). When ECU receives an on signal, it energizes control relay coil and supplies power to sensors and actuators. When ECU receives ST signal, it asserts engine is cranking and controls fuel injection rate, idle speed servo control, ignition timing, etc. for optimum cranking conditions.
INHIBITOR SWITCH (A/T MODELS)
Inhibitor switch is located on transaxle manual control lever. Inhibitor switch detects position of selector lever and sends signal to ECU. Based on this signal, ECU determines whether transaxle is in Neutral or Drive, then activates idle speed control servo to regulate idle speed.
MOTOR POSITION SENSOR (1.8L)
Motor position sensor is part of idle speed control servo, located on throttle body. (Scheme 7) Idle speed position sensor senses position of idle speed control servo's plunger and sends signal to ECU.
OXYGEN SENSOR
Oxygen sensor is located at outlet of exhaust manifold or turbocharger. Oxygen sensor monitors oxygen content of exhaust gasses and sends signal to ECU.
POWER STEERING PRESSURE SWITCH
Power steering pressure switch is located on side of power steering pump. Power steering pressure switch prevents idle speed from dropping due to power steering pump load, ensuring a stable idle speed. When steering wheel is turned and steering pump oil pressure increases, power steering pressure switch sends an on signal to ECU. When ECU receives signal, it activates idle speed control servo to increase idle speed to a preset RPM.
THROTTLE POSITION SENSOR (TPS)
Throttle position sensor, located on throttle body, is a variable resistor. Movable contact inside sensor rotates with throttle valve shaft, sensing throttle valve opening. As throttle valve shaft rotates, sensor output voltage changes. Based on signal generated by sensor, ECU detects throttle valve opening and determines engine operation mode (acceleration or deceleration).
VEHICLE SPEED SENSOR
Vehicle speed sensor, located in speedometer, is a reed-type sensor. (Scheme 4) Sensor converts transmission speedometer driven gear revolutions (vehicle speed) to pulse signals and sends them to ECU. Vehicle speed sensor generates 4 pulse signals for each rotation of speedometer driven gear.
Scheme 4
OUTPUT SIGNALS
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 on each output component, refer to the system indicated after component.
- A/C RELAY See MISCELLANEOUS CONTROLS.
- CHECK ENGINE Light See SELF-DIAGNOSTIC SYSTEM.
- EGR CONTROL SOLENOID VALVE See EMISSION SYSTEMS & SUB-SYSTEMS.
- FUEL INJECTORS See FUEL CONTROL under FUEL SYSTEM.
- FUEL PUMP RELAY See FUEL DELIVERY under FUEL SYSTEM.
- IDLE SPEED CONTROL SERVO See IDLE SPEED under FUEL SYSTEM.
- POWER TRANSISTOR(S) & IGNITION COIL(S) See IGNITION SYSTEM.
- PURGE CONTROL SOLENOID VALVE See EMISSION SYSTEMS & SUB-SYSTEMS.
- TURBOCHARGER PRESSURE CONTROL See AIR INDUCTION SYSTEM.
- TURBO METER CONTROL See AIR INDUCTION SYSTEM.
FUEL DELIVERY
Fuel is fed through the in-tank filter by electric fuel pump located in fuel tank. Passing through a second filter, fuel is maintained at a continuous pressure at the injectors by fuel pump and fuel pressure regulator.
FUEL PUMP
Fuel pump, located in fuel tank, consists of an impeller driven by a DC motor. Pump has an internal check valve to maintain system pressure, and a relief valve to protect fuel pressure circuit.
Relay, located on right side of center console, switches power to vehicle sensors and actuators, including airflow sensor, crank angle sensor, idle speed control, injectors and fuel pump. (Scheme 3)
When ignition is turned on, Electronic Control Unit (ECU) energizes relay coils (through inhibitor switch on automatic transaxle) to supply power to fuel pump. Relay failure will cause a no-start condition. Relay also sends signal to ECU. See FUEL PUMP RELAY (CONTROL RELAY) under INPUT DEVICES in this article.
FUEL PRESSURE CONTROL VALVE (TURBO MODELS)
If engine coolant temperature and intake air temperature are high when engine is started, ECU sends a signal to fuel pressure control valve. As a result, fuel pressure is increased and generation of fuel vapors caused by high temperature is suppressed. This maintains idle stability immediately after restarting under high temperature conditions.
FUEL PRESSURE REGULATOR
Fuel pressure regulator is located on fuel delivery pipe. Fuel pressure regulator maintains pressure of fuel delivered to injectors at a constant level of 47.6 psi (3.3 kg/cm 2 ) on non-turbo engines, or 36.3 psi (2.6 kg/cm 2 ) on turbo engines. Regulator is a diaphragm-operated relief valve with pressure applied by intake manifold vacuum. If intake manifold pressure becomes less than fuel pressure, relief valve opens, causing excess fuel to return to fuel tank.
FUEL INJECTORS
A fuel injector is located on each intake port. The injector is activated by an electric current controlled by the Electronic Control Unit (ECU). When current flows through injector solenoid coil, plunger and needle valve are magnetically attracted, causing injector nozzle to open and fuel to be injected. When current is interrupted, plunger and needle valve are pushed back by spring, closing injector nozzle. (Scheme 5)
Scheme 5
IDLE SPEED CONTROL SERVO (2.0L & 2.0L TURBO )
The idle speed control servo, located on throttle body, consists of a stepper motor. As motor operates, pintle extends or retracts to control by-pass airflow. (Scheme 6)
The ECU sends a signal to stepper motor, causing pintle to extend or retract. As pintle extends or retracts, the gap it forms between seat changes, controlling by-pass airflow.
Scheme 6
IDLE SPEED CONTROL SERVO (1.8L)
Idle speed control servo is located on throttle body. Idle speed control servo consists of a motor, worm gear, worm wheel and plunger. It also contains motor position sensor, which detects position of plunger and idle speed switch. Idle speed which detects idling condition of engine. (Scheme 7)
The worm gear is connected to motor shaft and transmits motor rotation to worm wheel. The worm wheel is linked with plunger by screw threads. When worm wheel turns, plunger extends or retracts.
When motor revolves on command from Electronic Control Unit (ECU), plunger either extends of retracts, depending on motor direction of rotation. The movement of plunger actuates throttle valve by means of idle speed control lever. When A/C is being operated, plunger extends and throttle valve opens wider so idle speed can be stabilized.
Scheme 7
ELECTRONIC IGNITION SYSTEM LASER (1.8L)
The electronic ignition system consists of a distributor, spark plugs, ignition coil, power transistor, Electronic Control Unit (ECU), high tension cables and wiring. The distributor incorporates power transistor, ignition coil and crank angle sensor. The ECU detects engine operating conditions from various sensor signals, and regulates ignition timing based on these signals.
When ignition switch is turned on, battery voltage is applied to ignition coil primary winding. As distributor shaft rotates, ignition signals are transmitted from ECU to power transistor. These signals activate power transistor, causing ignition coil primary winding current to repeatedly flow from ignition coil negative terminal through power transistor to ground, or be interrupted. This action induces high voltage in the secondary winding of ignition coil. From the coil, the secondary winding current flows through distributor and spark plug to ground, causing ignition in each cylinder.
ELECTRONIC IGNITION SYSTEM LASER (2.0L) & TALON
The ignition system is a 2-coil system that supplies sufficient energy for ignition at high speeds. A distributor is not used since Electronic Control Unit (ECU) directly activates power transistor for ignition timing control.
The ignition system has 2 power transistors and 2 ignition coils. Power transistor "A" controls primary current of ignition coil "A" to activate spark plugs in cylinders No. 1 and 4. Similarly, power transistor "B" controls ignition coil "B", which activates spark plugs in cylinders No. 2 and 3. In this way, spark plugs of 2 cylinders are activated, but actual ignition takes place only in the cylinder that is on its compression stroke at that time. Power transistors "A" and "B" are activated by signals from ECU, controlling the timing and firing of cylinders.
When ignition is turned on, battery voltage is applied to ignition coil primary winding. As crank angle sensor shaft rotates, ignition signals are transmitted from ECU to power transistor. These signals activate power transistor, causing ignition coil primary winding current to repeatedly flow from ignition coil negative terminal through power transistor to ground, or be interrupted. This action induces high voltage in secondary winding of ignition coil. From ignition coil, the secondary winding current flows through spark plug to ground, causing ignition in each cylinder.
IGNITION TIMING CONTROL SYSTEM 1.8L
Ignition timing control system is composed of various sensors, Electronic Control Unit (ECU) and power transistor. Depending on engine operating conditions, ignition timing control system functions to regulate ignition timing and current flow time of primary current, assuring good ignition performance. The on-off switching of the primary current flowing in the ignition coil is performed by power transistor, which in turn is regulated by ECU.
IGNITION TIMING CONTROL SYSTEM 2.0L & 2.0L TURBO
Ignition timing control system uses Electronic Control Unit (ECU). The ECU controls the timing and firing of cylinders based on signals from various engine sensors. The ECU activates power transistors so ignition occurs, taking into consideration operating conditions of engine. Optimum ignition timing control is determined by making preset corrections for engine coolant temperature, intake air temperature and other conditions of ignition advance angle, which are preset according to engine operating conditions. Engines with turbochargers have a knock sensor that corrects ignition advance angle according to presence or absence of knocking.
EXHAUST GAS RECIRCULATION (EGR) CONTROL
The EGR control system is designed to reduce oxides of nitrogen (NOx) in exhaust emissions. In this system, exhaust gas is partially recirculated from the exhaust manifold into intake manifold, while EGR flow is controlled by EGR valve. On federal vehicles, EGR system consists of an EGR valve and thermovalve. On California vehicles, EGR system consists of an EGR valve, EGR temperature sensor and EGR control solenoid valve.
EGR CONTROL SOLENOID VALVE (CALIFORNIA VEHICLES)
EGR control solenoid valve regulates EGR valve negative pressure (vacuum) activation. Pressure applied to EGR valve is controlled by solenoid valve through control relay.
EGR VALVE
The EGR valve is a diaphragm controlling the flow of EGR gases by opening and closing valve according to negative pressure (vacuum) acting on EGR spring. When negative pressure becomes stronger than EGR spring force, the EGR valve opens, allowing exhaust gases to flow into intake manifold.
Exhaust gas temperature sensor is located below EGR valve. Exhaust gas temperature sensor is a thermistor-type sensor. Sensor detects temperature of gas passage in EGR valve, converts detected temperature to an electric signal and sends signal to Electronic Control Unit (ECU). If sensor indicates a low exhaust gas temperature when EGR action is commanded, ECU can determine if an EGR fault is present.
THERMOVALVE (FEDERAL MODELS)
The thermovalve controls negative pressure (vacuum) acting on EGR valve in response to temperature of engine coolant. The valve opens at temperatures of 149°F (65°C) or lower, and closes at temperatures greater than 149°F (65°C).
CATALYTIC CONVERTER
The catalytic converter oxidizes carbon monoxide (CO) and hydrocarbons HC, and reduces oxides of nitrogen (NOx) present in exhaust gas to minimize emissions.
The catalytic converter uses a monolithic-type catalyst with a honey comb structure. The catalyst is supported by a stainless steel wire mesh and surrounded by a stainless steel shell.
PCV VALVE
A closed crankcase ventilation system is used to prevent blow-by gases from escaping into the atmosphere. This system has a PCV valve at the rocker cover. PCV system supplies fresh air to crankcase through the air cleaner. Fresh air is mixed with blow-by gases inside crankcase, and is passed through PCV valve into the intake manifold. The PCV valve has a metered orifice, through which the mixture of fresh air and blow-by gases are drawn into intake manifold in response to intake manifold vacuum.
EVAPORATIVE CONTROL
The evaporative emission control system prevents the escape of fuel vapors from fuel system into the atmosphere. When fuel tank is filled with fuel vapors generated inside fuel tank, vapors press and open overfill limiter valve, and pass through charcoal canister. Fuel vapors accumulated in the charcoal canister are taken to intake manifold, where they are burned.
CHARCOAL CANISTER
When engine is not running, fuel vapors generated inside fuel tank are absorbed and stored in the charcoal canister. When engine is running, fuel vapors absorbed into the charcoal canister are drawn into throttle body through purge control solenoid valve.
PURGE CONTROL SOLENOID VALVE
The purge control solenoid valve is an on-off control-type solenoid valve. It controls the introduction of purge air to intake air plenum from canister.
SELF-DIAGNOSTIC SYSTEM
The self-diagnostic system monitors all input signals from each sensor. If an abnormal input signal occurs, item is stored by the Electronic Control Unit (ECU) and is given a fault code number.
CHECK ENGINE LIGHT
CHECK ENGINE light comes on when ignition is turned on. Light remains on for several seconds after engine is started. The self-diagnostic system monitors all input signals from each sensor. If an abnormal input signal occurs, CHECK ENGINE light comes on and item fault is stored in memory by the ECU.
A/C RELAY
Note. Although these are not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.
A/C relay is located in relay box, next to right shock tower. (Scheme 8) When A/C is switched on, the ECU turns A/C compressor relay on to activate A/C compressor. To prevent vibrations or engine stalling due to activation of compressor, ECU controls A/C relay so A/C compressor is activated after a predetermined interval.
