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
All models use a water-cooled turbocharger, mounted on the exhaust crossover pipe. A wastegate assembly is attached to rear of turbine housing. The turbocharger consists of a turbine/compressor assembly, oil supply system, wastegate valve and a wastegate control solenoid valve. Other components include impellers, impeller shaft, bearings and impeller housings.
If intake boost pressure exceeds safe limits, engine damage may result. To prevent excessive intake boost pressure, the system uses a pressure-actuated wastegate valve as a limiting device. The wastegate valve opens when intake pressure exceeds a predetermined limit, allowing exhaust gases to by-pass the compressor.
Turbocharger operation requires a large quantity of clean oil to prevent bearing failure. Engine oil pressure provides constant lubrication to the system.
WASTEGATE CONTROL SOLENOID VALVE
Located in pressure line between intake manifold and wastegate valve, this duty solenoid compensates for reduced intake air volume due to high altitude. When Engine Control Unit (ECU) energizes solenoid, valve closes. This restricts pressure line, eliminating the wastegate valve by-pass function. Boost pressure is then unregulated (full volume). This maintains maximum allowable boost under high altitude conditions.
CARBURETED
Electronic Fuel Control (EFC) system is a computerized fuel, ignition and emission control system designed to maintain fuel economy and reduce vehicle emissions. An Electronic Control Unit (ECU) monitors data from various sensors and controls such functions as carburetor air/fuel mixture ratio, ignition timing and emission control devices.
PORT FUEL INJECTION (PFI)
PFI system is a computerized fuel, ignition and emission control system designed to maintain fuel economy and reduce vehicle emissions. Fuel is metered to intake system through a separate injector for each cylinder, mounted in intake manifold, next to intake valve. An Electronic Control Unit (ECU) monitors data from various sensors and controls such functions as fuel injector pulse width (fuel injector "on" time), ignition timing and emission control devices.
THROTTLE BODY INJECTION (TBI)
TBI system is a computerized fuel, ignition and emission control system designed to maintain fuel economy and reduce vehicle emissions. Fuel is metered to intake system through a single fuel injector, mounted to a throttle body on the intake manifold. An Electronic Control Unit (ECU) monitors data from various sensors and controls such functions as fuel injector pulse width (fuel injector "on" time), ignition timing and emission control devices.
ALL SYSTEMS
If a system fault (malfunction) occurs, a built-in fail-safe mechanism within the ECU controls fuel and ignition system functions according to preprogrammed values. This allows the vehicle to be driven, although driving performance is affected.
A self-diagnostic function allows the ECU to store trouble codes in its memory. CHECK ENGINE light informs the driver of system problems. If a system fault occurs, trouble codes which indicate system problems can be retrieved. For further self-diagnostic system information, see SELF DIAGNOSTICS.
INPUT DEVICES (CARBURETED)
Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the ECU. 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 usage on a specific model, see the appropriate wiring diagram in the WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section. The available input signals include the following
A/C ON SIGNAL
When A/C is turned on, ECU receives voltage signal and activates idle-up system. See IDLE SPEED under FUEL SYSTEM (CARBURETED) in this article.
COOLANT TEMPERATURE SENSOR
ECU applies reference voltage signal to this thermistor. Resistance value of sensor changes with variations in coolant temperature, causing reference voltage to increase or decrease. Sensor is equipped with 2 terminals. One terminal is used for ECU; other is for temperature gauge.
CRANK ANGLE SENSOR (ENGINE SPEED SENSOR)
Crank angle sensor is a magnetic pick-up coil sensing mechanism, located in distributor. Sensor provides crankshaft angle and engine RPM inputs to ECU.
ELECTRICAL LOADS
When headlights, heater blower or rear defogger are turned on, ECU receives voltage signal and activates idle-up system. See IDLE SPEED under FUEL SYSTEM (CARBURETED) in this article.
OXYGEN (O2) SENSOR
Generates voltage according to exhaust gas oxygen content. Voltage increases when oxygen content is low (rich), and decreases when oxygen content is high (lean). ECU determines air/fuel ratio based on voltage generated.
VACUUM/PRESSURE SENSOR & VACUUM LINE CONTROL SOLENOID VALVE
Senses changes in intake manifold vacuum and atmospheric pressure. Solenoid valve, in-line between intake manifold and vacuum/pressure sensor, receives voltage signal from ECU. With no voltage applied to solenoid valve, sensor monitors intake manifold vacuum. With voltage applied to solenoid valve, sensor monitors atmospheric pressure.
VEHICLE SPEED SENSOR (VSS)
ECU supplies voltage signal to one side of a tiny reed switch, located in speedometer assembly. Speedometer cable revolutions open and close reed switch, providing ECU with CONTINUITY/NO CONTINUITY input. ECU converts this signal to vehicle speed.
OUTPUT SIGNALS (CARBURETED)
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 in brackets after component.
CANISTER PURGE CONTROL (CPC) SOLENOID VALVE
See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS.
CHECK ENGINE LIGHT
See SELF DIAGNOSTICS.
COASTING FUEL CUT (CFC) SOLENOID
See FUEL CONTROL under FUEL SYSTEM (CARBURETED).
DUTY SOLENOID VALVE (DSV)
See FUEL CONTROL under FUEL SYSTEM (CARBURETED).
EGR CONTROL SOLENOID VALVE
See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS.
FLOAT CHAMBER VENT (FCV) SOLENOID VALVE
See FUEL EVAPORATION SYSTEM under EMMISSION SYSTEMS.
FUEL PUMP RELAY
See FUEL DELIVERY under FUEL SYSTEM (CARBURETED).
HIGH ALTITUDE COMPENSATOR (HAC) SOLENOID VALVE - FEDERAL
See FUEL CONTROL under FUEL SYSTEM (CARBURETED).
IDLE-UP CONTROL SOLENOID VALVE (ICSV)
See IDLE SPEED under FUEL SYSTEM (CARBURETED).
POWER TRANSISTOR
See IGNITION SYSTEMS.
SELF-DIAGNOSTICS
See SELF DIAGNOSTICS.
VACUUM LINE CONTROL SOLENOID VALVE & VACUUM/PRESSURE SENSOR
See INPUT DEVICES (CARBURETED).
INPUT DEVICES (FUEL INJECTION)
Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the ECU. 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 usage on a specific model, see appropriate wiring diagram in the WIRING DIAGRAMS article. The available input signals include the following
A/C SWITCH
Signals ECU of A/C operation.
AIRFLOW METER (EXCEPT JUSTY)
Hot-wire type airflow meter converts amount of air taken into engine into an electric signal by utilizing heat transfer between incoming air and a heating resistor (hot wire), located in air intake.
AIR TEMPERATURE SENSOR (JUSTY)
ECU applies reference voltage signal to this air-temperature sensitive thermistor, installed on air cleaner housing. Reference voltage increases and decreases with variations in air temperature.
ATMOSPHERIC PRESSURE SENSOR
Sensor is a component part of ECU. ECU uses this signal to compensate for variations in altitude, which affect air/fuel mixture ratios.
CAM ANGLE SENSOR (LEGACY)
Located on camshaft support on left cylinder bank. Pickup coil acts as triggering device. Based on signals received from triggering device, ECU distinguishes No. 1 cylinder from other cylinders. ECU then uses these signals to trigger distributorless ignition system and fuel injectors.
ECU applies reference voltage signal to this thermistor. Resistance value of sensor changes with variations in coolant temperature, causing reference voltage to increase or decrease.
CRANK ANGLE SENSOR (LEGACY)
Installed on oil pump, at front center of cylinder block. Pick-up coil acts as triggering device. Based on signals received from triggering device, ECU determines crankshaft angle. Based on these signals, ECU triggers distributorless ignition system and fuel injectors.
CRANK ANGLE & TDC (CYLINDER ID) SENSOR ASSEMBLY (EXC. LEGACY)
Assembly is located in distributor. On Justy, pick-up coil acts as triggering device. On Loyale, optical sensing unit (light emitting diode) acts as triggering device. Based on signals received from triggering device, ECU determines crankshaft angle and identifies No. 1 cylinder. Based on these signals, ECU triggers ignition system and fuel injector(s).
DETONATION (KNOCK) SENSOR
Installed on cylinder block, this sensor responds to cylinder block vibrations that result from detonation. If detonation occurs, a voltage is generated and sent to ECU. Based on the voltage received, ECU retards spark timing until detonation stops.
IDLE SWITCH
Signals control unit of closed throttle condition.
INHIBITOR SWITCH (A/T)
Signals ECU of transmission gear position.
NEUTRAL & PARK SWITCHES
Signals ECU of transmission gear position.
Generates voltage according to exhaust gas oxygen content. Voltage increases when oxygen content is low (rich), and decreases when oxygen content is high (lean). ECU determines air/fuel ratio based on voltage generated.
PRESSURE SWITCH (TURBO)
Mounted in front of body strut mount, this switch closes when intake manifold vacuum reaches approximately 2 in. Hg. This causes TURBO indicator light to illuminate, indicating turbocharging operation is in effect.
THROTTLE SENSOR (EXCEPT JUSTY)
Throttle sensor contains both a potentiometer (variable resistor) and an idle switch. Throttle position sensor sends ECU a potentiometer output signal corresponding to opening of throttle valve. Idle switch signal occurs when throttle is near idle position. ECU uses these signals to control air/fuel ratio during acceleration, deceleration and idling.
THROTTLE SWITCH (JUSTY)
This switch, attached to end of throttle shaft, indicates to the ECU that the throttle valve is closed, wide open (at least 50 degrees), or neither. This is NOT a variable resistor.
VEHICLE SPEED SENSOR
ECU supplies voltage signal to one side of a tiny reed switch, located in speedometer assembly. Speedometer cable revolutions open and close reed switch, providing ECU with CONTINUITY/NO CONTINUITY input. ECU converts this signal to vehicle speed.
OUTPUT SIGNALS (FUEL INJECTION)
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 in brackets after component.
AUXILIARY AIR VALVE
See IDLE SPEED under FUEL SYSTEM (FUEL INJECTION).
BY-PASS AIR CONTROL VALVE
See IDLE SPEED under FUEL SYSTEM (FUEL INJECTION).
CANISTER PURGE CONTROL (CPC) SOLENOID
See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS.
See SELF DIAGNOSTICS.
See IGNITION TIMING CONTROL SYSTEM under IGNITION SYSTEMS.
See IGNITION TIMING CONTROL SYSTEM under EMISSION SYSTEMS.
FAST IDLE CONTROL DEVICE (FICD) SOLENOID VALVE
See IDLE SPEED under FUEL SYSTEM (FUEL INJECTION).
FUEL INJECTOR RESISTOR PACK
See FUEL CONTROL (PFI) under FUEL SYSTEM (FUEL INJECTION).
FUEL INJECTOR(S) (FUEL CONTROL - TBI OR PFI)
See FUEL CONTROL (PFI) or FUEL CONTROL (TBI) under FUEL SYSTEM (FUEL INJECTION).
FUEL PUMP RELAY (FUEL DELIVERY - FUEL INJECTION)
See FUEL DELIVERY under FUEL SYSTEM (FUEL INJECTION).
POWER TRANSISTOR (IGNITION SYSTEM)
See IGNITION SYSTEMS.
SELF-DIAGNOSTICS (SELF-DIAGNOSTICS)
See SELF DIAGNOSTICS.
Fuel Pump
Electric fuel pump is located on crossmember under center of floor. Flow rate of fuel changes as pressure varies on delivery side. This controls required quantity of fuel delivered.
ECU provides power supply and ground for control circuit in fuel pump relay. When ignition is turned on with engine off, ECU energizes fuel pump relay for 3 seconds, activating fuel pump. After 3 seconds, ECU stops energizing fuel pump relay, unless ECU receives crank angle signal.
Located in carburetor, this solenoid responds to voltage signal from ECU to adjust air/fuel mixture through idle circuit during deceleration. This prevents overrich air/fuel mixtures during deceleration.
Located in carburetor, this ECU-controlled solenoid cycles on/off to control air/fuel mixture ratio entering slow speed and main metering passages.
Electric Choke
When fuel pump relay is energized, voltage is applied to electric choke heater element. Voltage is applied to choke heater under same conditions as fuel pump. See FUEL PUMP RELAY under FUEL DELIVERY of FUEL SYSTEM (CARBURETED) in this article.
High Altitude Compensator (HAC) Solenoid Valve (Federal)
To compensate for richer air/fuel mixtures at higher altitudes (26.38 in. Hg or less), HAC admits air into main metering passage. When vacuum/pressure sensor indicates barometric pressure has reached predetermined specification, ECU energizes HAC solenoid. This opens valve, admitting more air into main metering passage.
Hot Idle Compensator
Bimetallic heat sensor located inside air filter housing. Allows more idle air through idle circuit at high engine temperatures.
Compensates for decrease in engine RPM due to cold engine temperatures, increased electrical load (alternator loading) and A/C compressor load. See INPUT DEVICES under FUEL SYSTEM (CARBURETED) in this article.
When ECU receives input signals which indicates engine RPM has dropped, ECU energizes Idle-Up Control Solenoid Valve (ICSV). ICSV controls vacuum supply to throttle opener diaphragm. When vacuum is applied to throttle opener diaphragm, throttle plate opens to compensate for decrease in engine RPM.
Impeller-type pump is used. On Justy and Legacy, fuel pump is located in fuel tank. On Loyale, XT and XT6, fuel pump is mounted to underbody near fuel tank.
On all models, fuel pump pressurizes fuel through in-line filter to fuel injector rail. Fuel pump receives battery power through fuel pump relay.
ECU energizes fuel pump relay based on inputs from the ignition switch and ignition coil. During cranking, the ignition switch cranking circuit supplies current to energize the fuel pump relay. After engine starts and key is released to RUN position, ECU provides fuel pump relay ground. This activates fuel pump.
Fuel Pressure Regulator
Regulator maintains constant fuel system pressure by bleeding off fuel at injector rail back to fuel tank. Intake manifold vacuum acts on regulator diaphragm to control position of bleed-off valve in regulator.
Fuel Pulsation Damper (Justy)
This device, located on fuel injector rail, absorbs fuel pressure pulsations.
Fuel Injector
Fuel is supplied to engine through a single throttle body injector valve, mounted to intake manifold. ECU controls length of time injectors remain energized (pulse width) which affects amount of fuel metered through injectors. ECU triggers injectors based on signals received from crank angle sensor.
Fuel Injectors
Fuel is supplied to engine through injector valves, located at intake manifold, near intake valve opening. ECU controls length of time injectors remain energized (pulse width) which affects amount of fuel metered through injectors. ECU triggers injectors based on signals received from crank angle sensor.
Fuel Injector Resistor Pack (Loyale PFI & XT)
Positioned in series between fuel injector power source and ground. Regulates current flow through fuel injectors.
Auxiliary Air Valve (Loyale PFI & XT)
Increases idle air volume when engine ambient temperatures are low. Valve consists of a coiled bimetallic spring, a shutter valve, and an electric heater element. Shutter valve closes gradually to decrease airflow. Current to heater is supplied by fuel pump relay circuit.
By-Pass Air Control Valve (Legacy)
Consists of coolant temperature-sensitive bimetallic valve and ECU-controlled duty solenoid. Bimetallic valve compensates for varying engine temperatures. ECU cycles duty solenoid on/off, regulating amount of air which by-passes throttle valve. System compensates for idle speed decreases due to cold engine temperatures, A/C operation and electrical loads (alternator loading). System also provides dashpot function to prevent overrich air/fuel mixture ratios on deceleration.
By-Pass Air Control Valve (Loyale TBI & XT6)
An air passage by-passing throttle valve is provided to control idle air intake volume. ECU cycles duty solenoid on/off, regulating amount of air which by-passes throttle valve. System compensates for idle speed changes due to cold engine temperatures, A/C operation and varying altitude.
Fast Idle Control Device (FICD) Solenoid Valve (Justy)
Valve is located in-line between air filter housing and intake manifold. When A/C is turned on, ECU energizes solenoid valve. Solenoid valve opens, allowing fresh air to by-pass throttle valve through solenoid valve into intake manifold.
Idle Speed Control (ISC) Solenoid Valve (Justy)
Valve is mounted on air filter housing, in-line between air filter housing and intake manifold. At idle, ECU opens and closes solenoid valve. This allows fresh air to by-pass throttle valve through solenoid valve into intake manifold.
Thermal Air Valve (Justy)
Coolant temperature sensitive wax pellet valve allows idle air to by-pass throttle valve. This increases idle RPM during cold engine conditions.
Acts as primary current switching device for ignition system. When ECU signals power transistor base, primary current is allowed to flow to ground.
Justy
Magnetic pick-up coil sensing mechanism (crank angle sensor) in distributor signals ECU of crankshaft angle and distinguishes between No. 1 cylinder and other cylinders. Based on these inputs, ECU signals power transistor base, allowing primary current to flow to ground through ignition coil.
On carbureted engines, ignition coil receives battery voltage from ignition switch. On PFI engines, ignition coil receives battery voltage from ignition relay. Ignition relay is energized with ignition switch in ON or START position.
Loyale, XT & XT6
Optical sensing unit (crank angle sensor) in distributor signals ECU of crankshaft angle and identifies No. 1 cylinder. System consists of distributor (crank angle sensor), ignition coil and power transistor.
Based on input from crankshaft angle sensor, ECU signals base of power transistor. This allows primary current flow to ground. Ignition coil receives primary power supply when ignition coil relay is energized.
Legacy
Controlled by ECU, consists of 2 ignition coils and a power transistor assembly. Power transistor assembly consists of 2 transistors which control primary current path to ground for each ignition coil. One transistor controls primary path to ground for ignition coil which fires cylinders No. 1 and 2. Other transistor controls primary path to ground for ignition coil which fires cylinders No. 3 and 4.
Although each coil fires 2 plugs at the same time, ignition takes place in only one cylinder since the other cylinder is on its exhaust stroke when plug fires. Based on input from crankshaft and camshaft angle sensors, ECU signals base of appropriate power transistor. This allows primary current flow to ground. Ignition coils receive primary power supply when ignition coil relay is energized.
Detonation Retard Operation
When engine knock (detonation) is present, a signal is generated by knock sensor and is sent to ECU. ECU retards spark timing until engine knocking stops, then gradually advances spark timing.
Ignition Timing Advance Control
On all models, ignition timing advance is controlled by ECU. Based on sensor input signals, ECU adjusts ignition timing to preprogrammed advance and retard specifications.
AIR INJECTION SYSTEM
The purpose of the air injection system, is to reduce exhaust emissions by oxidizing hydrocarbons (HC) and carbon monoxide (CO). System is composed of a one-way air suction valve (pulse air valve), air cleaner, various hoses and tubing.
Negative pressure from exhaust pulsation reaches suction valve through a suction pipe. This causes reeds in suction valve to draw open. Secondary (fresh) air from air cleaner is drawn into exhaust passages. When positive pressure is present in exhaust, reeds are closed to prevent reverse flow of exhaust gas.
EXHAUST GAS RECIRCULATION (EGR)
EGR lowers oxides of nitrogen (NOx) exhaust emissions by admitting exhaust gases back into intake system. Exhaust gases lower peak combustion temperatures, which lowers NOx emissions.
EGR valve diaphragm receives operating vacuum through EGR control solenoid valve. ECU controls operation of EGR control solenoid valve.
On models with Canister Purge Valve (CPV), CPC solenoid valve is located in vacuum signal line between Canister Purge Valve (CPV) and ported vacuum source. See CANISTER PURGE VALVE (CPV). Under certain conditions, ECU energizes CPC solenoid valve. This allows ported vacuum signal to CPV.
On models without CPV, CPC solenoid valve is located in purge line between canister and ported vacuum source. Under certain conditions, ECU energizes CPC solenoid valve, allowing ported vacuum to purge the canister.
Canister Purge Valve (CPV)
Located on top of canister, this vacuum-controlled valve opens and closes purge line between intake manifold and canister. CPV valve remains closed at idle because ported vacuum activates its control diaphragm. When vacuum activates the control diaphragm, purge line is opened and stored vapors are free to be drawn into intake manifold.
Float Chamber Ventilation (FCV) Solenoid Valve
When ignition is off, this solenoid valve remains open to allow float bowl vapor to escape to canister. When ignition switch is in ON or START position, ECU energizes FCV solenoid valve, blocking off passage between float bowl and canister passage.
POSITIVE CRANKCASE VENTILATION (PCV)
PCV system draws crankcase blow-by, vapors and gases into combustion system rather than allowing then to escape to atmosphere. Crankcase gases mix with air/fuel mixture and are burned in combustion chamber. When engine is running, manifold vacuum pulls PCV valve open allowing crankcase fumes to enter intake manifold. If engine backfires, PCV valve is forced closed and stops any flow of gases. This prevents ignition of fumes in crankcase.
THERMOSTATIC AIR CLEANER (CARBURETED)
Thermostatic air cleaner reduces exhaust emissions by maintaining a uniform intake air temperature. System consists of an air cleaner housing, air stove on exhaust pipe and air intake hose between air cleaner and manifold stove. Air cleaner housing contains an air control diaphragm, air control valve, temperature sensor valve, flame arrester and connecting tubes and hoses.
All vehicles are equipped with a CHECK ENGINE light on instrument panel. Light illuminates when ignition switch is turned to ON position (bulb check) and when system malfunctions occur. For additional information, see TESTS W/CODES article in the ENGINE PERFORMANCE Section.