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.
COMPUTERIZED ENGINE CONTROLS
Computerized engine control system consists of various input devices which detect vehicle operating conditions. On all models, the Electronic Control Module (ECM) monitors input signals received from input devices and sends output signals to regulate air/fuel mixture and other engine control operations. This lowers exhaust emissions, while maintaining fuel economy and driveability.
System incorporates a self-diagnostic system, built-in fail-safe mechanism and back-up power. Self-diagnostic system provides capability of recognizing a system fault and storing a related trouble code in ECM memory for diagnostic purposes. Fail-safe mechanism substitutes preprogrammed sensor values to the ECM if a sensor fails, thus providing a certain level of engine performance. If ECM fails to operate properly, back-up power to ECM controls operation of fuel injectors based on signals from Manifold Absolute Pressure (MAP) sensor.
Samurai
The ECM is located under glove box. ECM distributes power to all sensors except oxygen and speed sensor, which generate their own voltage signal. ECM power (ECM terminals B1 and B7) is received from the EFI main relay. ECM back-up power (ECM terminal B9) is supplied from fuse box 15-amp fuse No. 7.
Sidekick
ECM is located under left side of dash. ECM distributes power to sensors (except oxygen sensor) and switches and controls ground circuits of solenoids. ECM power (ECM terminals B1 and B7) is received from the control relay. ECM back-up power (ECM terminal B9) is received from fuse box 15-amp fuse No. 3.
Swift DOHC
The ECM is located under left side of dash. ECM distributes power to all sensors except oxygen and speed sensor, which generate a voltage signal of their own. ECM power (ECM terminals A1 and A2) is received from the EFI main relay. ECM back-up power (ECM terminal A16) is received from main fuse.
Swift SOHC
The ECM is located under left side of dash. ECM distributes power to all sensors except oxygen and speed sensor, which generate their own voltage signal. ECM power (ECM terminal B1) is received from EFI main relay. ECM back-up power (ECM terminal B7) is received from 15-amp taillight fuse.
Note. Components are grouped into 2 categories. The first category is INPUT DEVICES, which are components that control or produce voltage signals monitored by the control unit. The second category is OUTPUT SIGNALS, which are components controlled by the control unit.
A/C Signal
See MISCELLANEOUS CONTROLS .
Air Temperature Sensor (Samurai & Swift SOHC)
On Samurai and Sidekick, air temperature sensor is located on side of intake manifold. On Swift SOHC, air temperature sensor is located on side of air cleaner. Air temperature sensor thermistor changes resistance with respect to temperature. High temperature causes low resistance. Low temperature causes high resistance. A reference voltage (supplied and monitored by ECM) is modified by sensor resistance. ECM uses this information to help determine control (output) signals to injector.
Airflow Meter (Sidekick & Swift DOHC)
Airflow meter, located between air cleaner and airflow meter outlet hose, consists of an airflow sensor and body. Airflow meter detects the amount of air drawn into engine and sends a voltage signal to ECM. ECM uses this signal to control fuel injectors.
Clutch Switch (Samurai)
Clutch switch is located above clutch pedal. Switch turns on when clutch pedal is depressed and off when pedal is released. ECM uses this signal to help determine control of fuel injector.
Coolant (Water) Temperature Sensor
On Samurai and Sidekick, coolant temperature sensor is located on side of intake manifold. On Swift DOHC, sensor is located on side of cylinder head. On Swift SOHC, sensor is located on side of throttle body.
Coolant temperature sensor thermistor changes resistance with respect to temperature. High temperature causes low resistance. Low temperature causes high resistance. A reference voltage (supplied and monitored by ECM) is modified by sensor resistance. ECM uses this information to help determine control signals to injector(s), emission components and timing devices (Samurai and Swift DOHC).
Crank Angle Sensor (Samurai, Sidekick & Swift SOHC)
Engine speed signal is generated (4 pulses per revolution) by the pick-up coil and reluctor assembly located in the distributor. ECM uses these pulses to calculate engine speed and to help determine control of fuel injector and ignition timing.
Crank Angle Sensor (Swift DOHC)
Engine speed signal is generated (12 pulses per revolution) by pick-up coil and reluctor assembly located in distributor. By providing 3 distinctive pulses for each cylinder, ECM is capable of more precisely timing engine control functions.
EGR Temperature Sensor (Samurai, Sidekick & Swift DOHC Calif)
The EGR temperature sensor is located in EGR passage on intake manifold. Sensor is used on California models only. Sensor thermistor changes resistance with respect to exhaust gas temperature. High temperature causes low resistance. Low temperature causes high resistance. Sensor resistance modifies a reference voltage, which is supplied and monitored by ECM. ECM uses EGR temperature sensor signal to determine if EGR action is occurring when requested by ECM.
Engine Start Signal
This signal is sent from starter circuit to ECM terminal B11 (terminal C1 on Swift DOHC or A1 on Swift SOHC). On Samurai and Sidekick, ECM uses signal to determine whether engine is cranking, to control fuel injection timing, injection time, Idle Speed Control (ISC) solenoid operation, throttle opener vacuum switching valve operation, and mixture heater operation (Sidekick A/T). On Swift DOHC, ECM uses this signal to determine whether engine is cranking and to control ignition timing. On Swift SOHC, ECM uses this signal to determine whether engine is cranking and to control fuel injector and fuel pump relay.
Gear Position Switch (Samurai Federal & Sidekick M/T)
Gear position switch is also known as 5th Gear Switch. Gear position is sensed when switch closes as transmission is shifted into 5th gear. Switch is open in all other gear positions. ECM uses on/off signal from gear position switch to control EGR vacuum switching valve.
Idle Switch
Idle switch is an integral part of throttle position sensor. Idle switch signals ECM of closed throttle condition. Switch is closed to ground at closed throttle (idle) and open at any position except closed throttle.
Ignition Signal (Samurai)
Ignitor sends ignition signal to ECM terminal A6. ECM uses this signal to help determine control of fuel injector.
Ignition Signal (Sidekick & Swift)
Ignition signal is sent to ECM terminal A1 (terminal A12 on Swift DOHC or B2 on Swift SOHC) from ignition coil. On Sidekick and Swift SOHC, ECM detects engine speed through this signal and uses it to control various actuators. On Swift DOHC, ECM uses this signal to detect if ignition spark is emitted and stops injector operation when signal is not received.
Oxygen (O2) Sensor
The O2 sensor is mounted in the exhaust manifold, where it comes in contact with exhaust gases as they enter the exhaust system. The O2 sensor generates voltage according to the oxygen content of exhaust gases. This voltage will vary from .1 volt (lean condition) to as high as 1.0 volt (rich condition). Sensor will not generate a voltage signal until it has reached operating temperature. Until sensor is warmed up, ECM will adjust air/fuel mixture based upon preprogrammed tables in ECM memory.
Park/Neutral (Shift) Switch (Sidekick A/T)
Park/neutral switch signals ECM on terminal B12 when transmission is in Park or Neutral. This input signal is used by ECM to help determine control of Idle Speed Control (ISC) solenoid.
Park/Neutral Switch (Swift A/T)
Automatic transmission ECM monitors park/neutral switch and relays a voltage signal to engine ECM when transmission is in Park or Neutral. This on/off input signal is used by ECM to help determine control of fuel injector(s) and Idle Speed Control (ISC) solenoid.
Power Steering Oil Pressure Switch (Sidekick & Swift SOHC)
ECM applies and monitors reference voltage to power steering pressure switch from ECM terminal A13. When steering wheel is turned, pressure switch closes, pulling reference voltage low. ECM uses this signal to help determine control of Idle Speed Control (ISC) solenoid.
Pressure Sensor (Samurai & Swift SOHC)
Pressure sensor is also known as Manifold Absolute Pressure (MAP) sensor. MAP sensor is connected to ECM by a 3-wire harness and to engine by a manifold vacuum hose. ECM applies a 5-volt reference signal from ECM terminal A23 (terminal A5 on Swift SOHC) to MAP sensor. MAP sensor has an internal mechanical resistor which varies resistance based on changes in engine load (manifold vacuum). As internal resistance varies, return voltage signal varies at ECM terminal A22 (terminal A4 on Swift SOHC). ECM interprets this voltage change as changes in engine load and uses this signal to help determine control of fuel injectors, Idle Speed Control (ISC) solenoid and EGR system.
Throttle Position Sensor (A/T)
ECM supplies throttle position sensor with a 5-volt reference signal. Sensor contains both a potentiometer (variable resistor) and an idle switch. Throttle position sensor sends ECM a potentiometer output signal corresponding to throttle valve opening and idle switch signal that turns on only when throttle is in idle position. ECM uses these signals to help determine control of air/fuel ratio during acceleration, deceleration and idle.
Vehicle Speed Sensor
Vehicle speed sensor is a P/M generator and switching transistor located in speedometer head. ECM supplies and monitors a voltage signal to speed sensor. As P/M generator rotates (vehicle moving), switching transistor in speed sensor grounds and ungrounds reference voltage signal from ECM terminal A10 (A11 on Swift SOHC). ECM uses this signal to help determine control of Idle Speed Control (ISC) solenoid and shift-up indicator light (Swift SOHC).
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.
Canister Purge Vacuum Switching Valve
See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS.
CHECK ENGINE Light
See SELF-DIAGNOSTIC SYSTEM .
EGR Vacuum Switching Valve
See EXHAUST GAS RECIRCULATION (EGR) under EMISSIONS SYSTEMS.
Fuel-Cut System
See FUEL CONTROL under FUEL SYSTEM.
Fuel Injector(s)
See FUEL CONTROL under FUEL SYSTEM.
Fuel Pump Relay
See FUEL DELIVERY under FUEL SYSTEM.
Idle Speed Control (ISC) Solenoid
See IDLE SPEED under FUEL SYSTEM.
Ignition Advance Control
See IGNITION TIMING CONTROL SYSTEM under IGNITION SYSTEM.
Lock-Up Solenoid Relay
See TRANSMISSION CONTROL under MISCELLANEOUS CONTROLS.
Throttle Opener Vacuum Switching Valve
See IDLE SPEED under FUEL SYSTEM.
Fuel Pump
Electric fuel pump is located in fuel tank. Fuel pump receives power when ECM provides ground to fuel pump relay. When power is supplied to fuel pump, motor and impeller inside pump turn. This causes a pressure difference to occur between both sides of impeller. When fuel is drawn through fuel pump inlet port, pressure is increased and discharged through outlet port.
The fuel pump also incorporates a relief valve to prevent excessive rise of discharge pressure and a check valve to keep residual pressure in fuel feed line when fuel pump is not activated.
Fuel pump relay is energized based upon ignition switch and RPM inputs. Power for fuel pump is supplied by EFI main relay, which receives its power from main fuse. EFI main relay is energized by ECM when the ignition is turned on.
Fuel Pressure Regulator
Fuel pressure regulator is a spring/vacuum operated diaphragm-type relief valve which maintains a constant regulated fuel pressure under all vehicle operating modes. When manifold vacuum is high (low fuel requirements), diaphragm is drawn in, counteracting spring pressure. In this condition, excess fuel is routed back to fuel tank. When manifold vacuum drops (engine load), spring pressure overcomes vacuum, closing off fuel tank return line. This maintains pressure and volume to injector(s).
Samurai, Sidekick and Swift SOHC use Throttle Body Injection (TBI), which incorporates a single fuel injector in the throttle body unit. Swift DOHC uses Port Fuel Injection (PFI), which incorporates 4 fuel injectors mounted in a fuel rail assembly.
When the solenoid coil of injector is energized by ECM, coil becomes an electromagnet. (Scheme 1)& 2. This lifts injector plunger, allowing fuel under pressure to be injected into intake manifold (Samurai, Sidekick and Swift SOHC) or cylinder head (Swift DOHC). Since fuel pressure is relatively constant, air/fuel mixtures are controlled solely by injector pulse width ("on" time). ECM determines proper pulse width based upon input signals received from various sensors and switches.
Timing of injector firing is determined by ECM based upon RPM signals received from either distributor P/M generator (Swift) or ignition coil (Samurai, Sidekick and Swift SOHC). On Swift SOHC, ECM also monitors ignition coil signal. Since ECM interprets coil signals as an indication of spark presence, fuel injector triggering will cease if ignition coil signal is lost.
Scheme 1
Scheme 2
Battery Voltage Compensation
A drop in battery voltage directly affects the pulse width of injector(s). As battery voltage drops, pulse width tends to decrease. This would cause a leaner air/fuel mixture than desired. To compensate for this, the ECM monitors battery voltage. If battery voltage drops, ECM will increase injector pulse width.
The fuel-cut system will stop fuel injection during deceleration to prevent excess fuel build-up during periods when oxygen is insufficient for combustion (i.e., closed throttle deceleration). Fuel-cut system will also deactivate injectors when engine speed exceeds 6800 RPM (Samurai, Sidekick and Swift SOHC) or 7500 RPM (Swift DOHC). This is done to prevent engine damage due to excessive engine speed. As engine speed drops to less than 6800 RPM (Sidekick), 7460 RPM (Swift DOHC), 6500 (Samurai) or 6600 (Swift SOHC), injection will once again occur.
Air Valve (Swift DOHC & SOHC)
Air valve is located on intake manifold. Air valve is used to increase idle speed (airflow) when engine is started at a low ambient temperature. Air valve consists of a thermowax pellet, spring and plunger. Water from cooling system passes through valve, directly across thermowax pellet.
When coolant temperature is low, thermowax pellet is contracted, allowing air to pass under end of plunger and into intake manifold. This air by-passes throttle plate, increasing idle speed for improved cold engine driveability. As coolant temperature increases, thermowax pellet expands, gradually blocking off by-passed air and decreasing idle speed.
An air passage by-passing the throttle valve is provided to route filtered air directly into intake manifold. ECM-energized ISC solenoid valve regulates airflow through this passage. Solenoid is located on side of throttle body.
Air is allowed to pass through ISC solenoid valve when it is energized. Solenoid is energized whenever idle speed drops to less than desired RPM due to engine load (i.e., electrical, A/C, P/S, automatic transmission in Drive, etc.). ISC solenoid valve is also energized each time engine is started and during periods of deceleration (to compensate for rich mixtures caused by a fully closed throttle). Duration of ISC solenoid valve operation is dependent on coolant temperature.
Throttle Opener Control System (Samurai)
When vehicle is first started, ECM energizes throttle opener Vacuum Switching Valve (VSV). This blocks manifold vacuum which normally draws throttle opener diaphragm and linkage rod to base idle position. Once vehicle is started, ECM will de-energize VSV. This allows manifold vacuum to pass through VSV to throttle opener diaphragm. Diaphragm will then retract, allowing throttle linkage to return to normal base idle position.
Throttle Opener Vacuum Switching Valve (Samurai)
Throttle opener is controlled by Vacuum Switching Valve (VSV) which opens and closes vacuum passage to throttle opener. ECM controls throttle opener VSV according to engine, starter and coolant (water) temperature sensor signals.
Samurai, Sidekick & Swift SOHC
The electronic ignition system consists of a distributor which utilizes a pick-up coil and reluctor to produce ignition pulses through the ignitor. Ignitor is also located within the distributor.
Power for ignition coil and ignitor is provided from fuse box 15-amp fuse (20-amp on Swift SOHC), which receives power when the ignition switch is in the ON position. Ground circuit for ignition coil is regulated by the ignitor. As the rotating reluctor passes pick-up coil pole piece, an alternating current is produced. The ignitor uses this alternating signal to determine when to ground and open primary ignition circuit.
When ignitor opens ground circuit for primary ignition, the magnetic field around ignition coil windings collapses, producing an induced high voltage surge which is used to fire spark plugs.
The ignition system consists of an ignition coil, a distributor containing a P/M generator crank angle sensor, trigger wheel and rotor, and an ignition power unit which opens and closes ignition coil primary circuit based upon signals from ECM. When power unit removes the ground circuit from primary ignition, the magnetic field around ignition coil windings collapse. This produces an induced high voltage surge which is used to fire spark plugs.
Power for ignition coil is provided from fuse box 20-amp ignition fuse when ignition switch is in ON position. Tachometer signal generated by triggering of ignition coil is monitored by ECM at terminal A12 after signal passes through a noise suppressor filter.
Advance Control
Ignition timing is controlled by ECM based upon sensor input signals. ECM controls ignition timing to a precise point by matching vehicles operating conditions to preprogrammed timing advance specifications stored in ECM memory. Signals generated by crank angle sensor are transmitted to ECM. These signals are modified by input signals from coolant (water) temperature sensor, airflow meter, throttle position sensor, idle switch, vehicle speed sensor and monitored battery voltage.
EMISSION SYSTEMS
For additional information, see EMISSION APPLICATION S and VACUUM DIAGRAMS articles in the ENGINE PERFORMANCE Section.
EXHAUST GAS RECIRCULATION (EGR)
To lower oxides of nitrogen (NOx) exhaust gas emissions, an EGR system is used. (Scheme 3) The EGR system introduces exhaust gases into intake system. The exhaust gases are noncombustible gases which, when combined with incoming air/fuel mixture, lower peak combustion chamber temperatures.
EGR valve receives ported operating vacuum through an ECM-regulated EGR Vacuum Switching Valve (VSV). ECM regulates VSV based upon input signals from various sensors. Control vacuum is further regulated by an EGR modulator, located in vacuum line between EGR valve and EGR solenoid.
Scheme 3
EGR Temp Sensor (Samurai, Sidekick & Swift DOHC Calif.)
The EGR temperature sensor is located in EGR passage on intake manifold. Sensor thermistor changes resistance with respect to exhaust gas temperature. High temperature causes low resistance. Low temperature causes high resistance. A reference voltage (supplied and monitored by ECM) is modified by sensor resistance. ECM uses this information to determine if EGR action is occurring when requested by ECM.
EGR Modulator
EGR Modulator is also known as a backpressure transducer. On Swift, EGR modulator is used on California models only. EGR modulator is used to help regulate EGR action. Modulator will allow ported vacuum signal to bleed off to atmosphere until exhaust gas backpressure in hollow modulator stem closes vacuum bleed. At this time vacuum will pass through modulator and activate EGR valve.
EGR Vacuum Switching Valve (VSV)
EGR valve receives ported operating vacuum through an ECM-regulated EGR vacuum switching valve. ECM regulates VSV based upon signals from various sensors.
Charcoal Canister (Samurai, Sidekick & Swift DOHC)
When engine is not running, vapor caused by expanding fuel in fuel tank collects in fuel vapor separator. (Scheme 4) Fuel which condenses in fuel vapor separator returns to fuel tank. Fuel vapor flows from fuel vapor separator and into charcoal canister where it is contained by activated charcoal. When engine is started, ported vacuum causes fresh air to be drawn in through bottom of canister. This pulls stored fuel vapor into the combustion chamber for burning.
On Swift DOHC, fuel vapor purge line is regulated by ECM operated canister purge vacuum switching valve. Vacuum switching valve allows purge to occur only under following conditions
- Coolant temperature is greater than 140°F (60°C).
- Engine speed is greater than 1500 RPM.
- Throttle switch is in OFF position (not idling).
- Engine is under load.
Scheme 4
Charcoal Canister (Swift SOHC)
The vapors generated in fuel tank pass through a 2-way check valve and enter charcoal canister where charcoal absorbs and stores fuel vapors. Canister is purged or cleaned by air drawn through the filter at bottom of canister and sucked into intake manifold through purge control valve and purge line. Throttle body vacuum is applied to canister purge control valve to open valve under following conditions
- Engine is running.
- Engine is at operating temperature.
- Throttle valve opens larger than idle position.
When engine coolant temperature is low, Bimetallic Vacuum Switching Valve (BVSV) opens to atmosphere, causing throttle body vacuum not to be applied to purge control valve, therefore closing purge control valve and not allowing vapors to purge into intake manifold.
Canister Purge Vacuum Switching Valve (Swift DOHC)
ECM controls canister purge Vacuum Switching Valve (VSV) according to signals from various sensors. When ECM signals VSV, fuel vapors flow from charcoal canister into combustion chambers for burning.
Fuel Vapor Separator (Samurai, Sidekick & Swift DOHC)
When engine is not running, vapor from expanding fuel in fuel tank collects in fuel vapor separator. Fuel which condenses in fuel vapor separator returns to fuel tank. Fuel vapor flows from fuel vapor separator into charcoal canister where it is contained by activated charcoal. When engine is started, ported vacuum purges stored vapors from canister.
POSITIVE CRANKCASE VENTILATION (PCV)
PCV system consists of PCV valve, 3-way joint and crankcase hoses from air cleaner and rocker cover, teeing at PCV valve. System draws crankcase blow-by gases (hydrocarbons) into air induction system rather than allowing them to escape to atmosphere. Crankcase gases are mixed with air/fuel mixture and burned in combustion chamber.
SELF-DIAGNOSTIC SYSTEM
When a system fault occurs, CHECK ENGINE light on dash will glow to inform driver a problem exists. Light will remain on until fault goes away or system is serviced. If fault goes away (system parameter returns to normal operation) before it is serviced, CHECK ENGINE light will go out. Related fault code will still remain in ECM memory until cleared. Stored codes may later be accessed and identified by counting flashes of CHECK ENGINE light.
All vehicles are equipped with a CHECK ENGINE light located on the instrument panel. CHECK ENGINE light will glow when ignition switch is turned to ON position (bulb check) and engine is not running. Light should not flash at this time and should go out when engine is started.
Samurai & Sidekick (Federal)
The CHECK ENGINE light will automatically flash at 50,000, 80,000 and 100,000 miles on a warmed running vehicle. This does not indicate a system fault; it indicates system inspection and/or system component replacement is required. After necessary services have been performed, turn off CHECK ENGINE light by moving cancel switch to opposite position. Cancel switch is located below steering column lower trim panel.
- At 50,000 Miles - Replace PCV valve, inspect EGR system.
- At 80,000 Miles - Replace O2 sensor.
- At 100,000 Miles - Replace PCV valve, inspect catalytic converter for plugging, inspect EGR system, replace O2 sensor, replace charcoal canister, inspect ECM and related sensors.
MISCELLANEOUS CONTROLS
Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.
This signal is sent from A/C amplifier to ECM terminal A2 (Samurai and Sidekick), A18 (Swift DOHC) or B5 (Swift SOHC). ECM uses this signal to detect when A/C is operating and sends a signal to Idle Speed Control (ISC) solenoid to increase idle speed.
Lock-Up Solenoid (Sidekick A/T)
When ECM senses conditions are correct for energizing lock-up solenoid in automatic transmission, ECM will energize lock-up relay. Relay, in turn, energizes lock-up solenoid. When energized, the lock-up solenoid provides a feedback signal to ECM, indicating lock-up signal has been received. This is not a true indication that physical lock-up has occurred.
Lock-Up Solenoid Relay (Sidekick A/T)
Battery voltage is supplied to lock-up relay Light Green/Red wire from control relay terminal "E". Battery voltage is supplied to lock-up relay White/Red wire through stoplight switch. Voltage through stoplight switch should drop to zero volts when brake pedal is depressed. When ECM senses conditions are correct for energizing lock-up solenoid in automatic transmission, ECM will energize lock-up relay by providing ground on ECM terminal A11. Relay, in turn, energizes lock-up solenoid. When energized, lock-up solenoid will provide a feedback signal to ECM, indicating lock-up signal has been received.
Throttle Valve Output Signal (Swift A/T)
Engine ECM converts throttle valve input signals into simple on and off signals which it transmits to the automatic transmission ECM. When gear selector is in "D" or "2", automatic transmission ECM uses these signals to determine proper gear selection. When gear selector is in D, transmission will select and shift transmission into 1st, 2nd or 3rd gear. When gear selector is in "2" position, ECM will select and shift between 1st or 2nd gear.