COMPUTERIZED ENGINE CONTROLS
Fuel injection system is Throttle Body Injection (TBI). The electronic fuel injection engine control system monitors vehicle operating conditions through input signals and regulates air/fuel mixture and other engine control operations by output signals. This lowers exhaust emissions while maintaining fuel economy and driveability.
The control systems have a fail-safe mechanism. If a fault occurs while driving, the system will substitute pre-programmed values. Driving performance will be affected, but vehicle may still be driven. These systems have a self-diagnostic feature capable of recognizing a system fault and storing a related trouble code in memory for future retrieval and diagnosis.
ENGINE CONTROL MODULE (ECM)
Note. ECM is also known as Powertrain Control Module (PCM). All references to ECM include PCM unless specified otherwise.
Note. For ECM locations, see ECM LOCATION table.
Power for ECM is supplied through the TAIL/DOME fuse, located in fuse block. The ECM distributes power or controls ground of various sensor, switches and solenoids for engine control.
| Application | Location |
|---|---|
| Tracker | Under Left Side Of Dash, Near Kick Panel |
ECM LOCATION
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 ECM. The second category is OUTPUT SIGNALS, which are components controlled by the ECM.
INPUT DEVICES
Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input device usage on a specific model, see appropriate wiring diagram in WIRING DIAGRAMS article in this section. The available input signals include the following
A/C Signal
On models with A/C, a signal is sent to the ECM when A/C is operating. The ECM uses this signal with other inputs to determine idle speed and fuel mixture.
Camshaft Position (CMP) Sensor
Engine speed signal is generated by pick-up coil/camshaft position sensor and signal rotor in the distributor. This pulsing signal is sent to ECM, where it is used to calculate engine speed.
Crank Signal
Engine start signal, sent from starter circuit, is used by ECM to determine when engine is cranking. Using this signal, ECM calculates fuel injection timing, Idle Air Control (IAC) valve and throttle opener solenoid vacuum valve.
EGR Temperature Sensor (California)
The EGR temperature sensor is located at base of EGR valve. Reference voltage, supplied and monitored by ECM, is modified by sensor resistance. Sensor resistance changes with respect to exhaust gas temperature. High temperature causes low resistance. Low temperature causes high resistance. ECM uses this information to determine if EGR is functioning.
Engine Coolant Temperature (ECT) Sensor
Engine Coolant Temperature (ECT) sensor monitors coolant temperature. A reference voltage (supplied and monitored by ECM) is modified by sensor resistance, which changes according to temperature. High coolant temperature causes low resistance and low coolant temperature causes high resistance. The ECM uses this information to control fuel injectors and emission components.
Ignition Signal
Ignition system circuit sends a signal to ECM. ECM detects status of ignition coil and uses signal for controlling various circuits and devices.
Intake Air Temperature (IAT) Sensor
Intake air temperature sensor measures intake manifold air temperature. The IAT sensor resistance changes with respect to temperature. High air temperature decreases IAT sensor resistance. Low air temperature increases IAT sensor resistance.
Sensor resistance modifies a reference voltage that is supplied and monitored by ECM. The ECM uses this information to control output signals to the fuel injectors.
For IAT sensor locations, see INTAKE AIR TEMPERATURE SENSOR (IAT) LOCATION table.
| Application | Location |
|---|---|
| Tracker | On Air Intake Manifold |
INTAKE AIR TEMPERATURE SENSOR (IAT) LOCATION
Oxygen (O2) Sensor
O2 sensor is mounted in exhaust manifold or exhaust pipe, where it contacts exhaust gases. O2 sensor generates voltage according to oxygen content in exhaust gases. Voltage will vary from .1 volt (lean condition) to as high as one volt (rich condition).
Sensor will not generate a voltage signal until it reaches operating temperature. Sensor sends voltage signal to ECM, which uses it to obtain correct emissions by adjusting air/fuel ratio. Until sensor is warmed up, ECM adjusts air/fuel mixture based upon preprogrammed ECM memory.
On Tracker, a heated oxygen sensor is used. This sensor works the same way as the non-heated sensor, except the O2 sensor is heated for more precise determination of exhaust gas oxygen concentration.
Park/Neutral Switch (A/T)
On A/T applications, ECM monitors switch position and receives a voltage signal when transaxle/transmission is in any forward or reverse gear. The ECM uses this input signal to help control fuel injectors.
Power Steering Pressure Switch
Power steering pressure switch indicates to the ECM when power steering pressure is applied. ECM uses this signal to alter engine speed.
Throttle Position Sensor
ECM supplies throttle position sensor with a 5-volt reference signal. Throttle position sensor contains a variable resistor and idle switch. Throttle position sensor sends an output signal to ECM corresponding to opening of throttle valve and idle switch signal (only when throttle is in idle position).
ECM uses these signals to control air/fuel ratio during acceleration, deceleration and idling. These signals are also used to determine idle speed.
Vehicle Speed Sensor
Vehicle Speed Sensor (VSS) consists of a reed switch built into speedometer head. ECM supplies VSS with a 5-volt reference signal. As speedometer cable rotates, the reed switch closes the circuit to ground 4 times per revolution. As vehicle speed increases, frequency of ground pulses increase. This pulse is sent to ECM and interpreted as vehicle speed.
OUTPUT SIGNALS
Note. Vehicles are equipped with various combinations of computer-controlled components. Not all components listed are used on every vehicle. For theory and operation on each output component, refer to the system indicated after component.
A/C Vacuum Switching Valve (VSV)
See IDLE SPEED under FUEL SYSTEM.
Circuit Opening Relay
See FUEL DELIVERY under FUEL SYSTEM.
Distributor Ignitor
See IGNITION SYSTEM .
ECM Main Relay
See FUEL DELIVERY under FUEL SYSTEM.
EFI F-HTR Relay
See FUEL DELIVERY under FUEL SYSTEM.
EGR Vacuum Switching Valve
See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS.
EVAP Canister Purge Control Solenoid
See FUEL EVAPORATIVE SYSTEM (EVAP) under EMISSION SYSTEMS.
FI Main Relay
See FUEL DELIVERY under FUEL SYSTEM.
Fuel-Cut System
See FUEL CONTROL under FUEL SYSTEM.
Fuel Injector
See FUEL CONTROL under FUEL SYSTEM.
Fuel Pump Relay
See FUEL DELIVERY under FUEL SYSTEM.
Idle Air Control (IAC) Valve
See IDLE SPEED under FUEL SYSTEM.
Main Relay
See FUEL DELIVERY under FUEL SYSTEM.
Malfunction Indicator Light
See SELF-DIAGNOSTIC SYSTEM .
Shift Indicator Light
See TRANSMISSION CONTROL under MISCELLANEOUS CONTROLS.
Throttle Opener Solenoid Vacuum Valve
See IDLE SPEED under FUEL SYSTEM.
Throttle Position Sensor Output Signal
See TRANSMISSION CONTROL under MISCELLANEOUS CONTROLS.
The main relay is mounted on the ECM, located under left side of instrument panel, near kick panel. When ignition is turned on, ECM grounds the main relay and provides voltage to fuel pump relay. The ECM grounds fuel pump relay, and power is then supplied to the fuel pump.
Fuel Pump
Electric fuel pump is located in the fuel tank. Fuel pump delivers fuel to fuel injectors where system pressure is controlled by fuel pressure regulator. Fuel pump contains an internal check valve to maintain pressure in fuel lines after fuel pump is turned off.
Fuel pump relay is mounted on the ECM, located under left side of instrument panel, near kick panel. When ignition is turned on, ECM grounds the main relay and provides voltage to the pump relay. ECM will ground the fuel pump relay and provide power to fuel pump.
Fuel pump will operate as long as engine is cranking or running and ECM is receiving ignition reference pulses. If no ignition references are received, ECM will shut off fuel pump.
Fuel Pressure Regulator
Regulator is a spring/vacuum-operated, diaphragm-type relief valve which maintains a regulated fuel pressure under all conditions. 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 fuel injectors.
Battery Voltage Signal
The ECM monitors battery voltage. A drop in battery voltage directly affects fuel injector pulse width. As battery voltage drops, pulse width decreases, causing a leaner air/fuel mixture. ECM compensates by increasing pulse width to provide richer mixture.
The fuel-cut system will stop fuel injection during deceleration to prevent unburned gases from being exhausted. Fuel-cut system will also deactivate injectors when engine speed exceeds 6800 RPM. This prevents engine damage due to excessive engine speed. As engine speed drops to less than 6500 RPM, fuel injection will once again occur.
When fuel injector solenoid coil is energized by the ECM (on time), coil becomes an electromagnet. This opens the fuel injector, allowing fuel to be injected into the intake manifold or cylinder. The air/fuel mixtures are controlled by the fuel injector pulse width (on time). The ECM determines proper pulse width based upon input signals from various sensors and switches.
Fuel injection timing is determined by ECM based upon RPM signals received from either the distributor or ignition coil. Tracker has Throttle Body Injection (TBI), which incorporates a single fuel injector in throttle body unit.
When A/C is operated, ECM receives a signal and controls A/C VSV operation. The A/C VSV supplies a certain amount of by-pass air to create a lean condition. ECM uses this signal to adjust air/fuel mixture and increase engine speed to prevent stalling.
Fast Idle Air Valve
Fast idle air valve is used to increase idle speed when engine coolant is less than 140°F (60°C). The coolant temperature alters the thermowax pellets to increase or decrease air into the intake manifold.
When coolant temperature is less than specified, valve opens by spring pressure, allowing air into intake manifold. This increased airflow increases the idle speed. As coolant temperature increases, valve closes and shuts off the airflow, causing idle speed to decrease. When engine coolant temperature is greater than 140°F (60°C), valve fully closes and normal idle speed is obtained.
The IAC valve is located on left side of engine, or on right side of throttle body. The IAC valve by-passes air around throttle valve directly into the intake manifold. Air is allowed to pass through IAC valve when it is energized by the ECM. IAC valve is energized whenever idle speed drops to less than desired RPM due to engine load (i.e., electrical,P/S, A/T in Drive, etc.).
The IAC 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.
Throttle Opener Control System
When vehicle is first started, ECM activates a Throttle Opener Solenoid Vacuum (TOSV) valve, which supplies vacuum to the throttle opener. The ECM controls TOSV valve according to ignition signal, starter signal and signal from Engine Coolant Temperature (ECT) sensor. The TOSV valve is activated for .2-35 seconds after engine starts, depending on ECT sensor.
Energizing the TOSV valve opens a vacuum passage between TOSV valve filter and throttle opener, and closes the manifold vacuum passage. When vacuum passage is closed, diaphragm spring pushes on throttle linkage, increasing throttle opening.
Once vehicle starts, ECM de-energizes the TOSV valve, allowing manifold vacuum to pass through TOSV valve to throttle opener diaphragm. Diaphragm will retract, allowing throttle linkage to return to normal base idle position.
ELECTRONIC IGNITION SYSTEM
Ignition system consists of a distributor, which uses a signal generator (signal rotor and pick-up coil/Camshaft Position (CMP) sensor) to produce ignition pulses through the externally mounted ignitor. Ignitor is mounted on right side of firewall in engine compartment.
Power for ignition coil and ignitor is provided through 15 amp IG-COIL METER fuse, located in fuse block below left side of steering column. Fuse receives power when ignition is turned on. Ground circuit for ignition coil is regulated by the ECM.
As rotating signal rotor passes pole piece of pick-up coil/CMP sensor, a reference signal is sent to ECM, which uses this signal to determine when to signal ignitor to open ground circuit for primary ignition.
When ignitor opens ground circuit for primary ignition, magnetic field around ignition coil windings collapses, producing an induced high voltage surge used to operate the spark plugs.
Ignition Timing Advance Control
ECM controls ignition timing based upon various sensor input signals.
EXHAUST GAS RECIRCULATION (EGR)
An Exhaust Gas Recirculation (EGR) system is used to lower oxides of nitrogen (NOx) exhaust gas emissions. The EGR system introduces exhaust gases into intake system. Exhaust gases are noncombustible gases which, when combined with the incoming air/fuel mixture, lowers peak combustion chamber temperatures.
The EGR valve receives ported vacuum signal from an ECM-regulated EGR Vacuum Switching Valve (VSV). Various inputs to ECM are used to determine EGR operation. On California models, EGR valve operation is monitored by ECM through signal from EGR temperature sensor. The EGR temperature sensor monitors exhaust gas temperature. If abnormal temperature exists, Malfunction Indicator Light (MIL) will be activated.
The vacuum signal to EGR valve is further controlled by a vacuum modulator located in the vacuum line between the EGR-VSV and the EGR valve.
Under low driving speeds and light load conditions, vacuum modulator diaphragm is pushed downward and opens vacuum modulator. This allows air to enter modulator from the outside, reducing vacuum supply to EGR valve. The EGR valve closes slightly, reducing amount of recirculated exhaust gases.
Under high driving speeds and heavy load conditions, vacuum modulator diaphragm is pushed upward, closing vacuum modulator. This increases vacuum supply to EGR valve and valve opens slightly, increasing amount of recirculated exhaust gases.
Under following conditions, ECM does not allow EGR operation
- Barometric pressure is low.
- Coolant temperature is low.
- Engine is operating under heavy load.
- Engine speed exceeds 6000 RPM.
- Intake manifold pressure is low.
- Throttle valve is at idle position.
- A/T is in lock-up condition.
EGR temperature sensor resistance changes with respect to exhaust gas temperature. High exhaust gas temperature decreases sensor resistance. Low exhaust gas temperature increases sensor resistance. A reference voltage, supplied and monitored by ECM, is modified by sensor resistance. ECM uses this information to determine EGR operation.
FUEL EVAPORATIVE SYSTEM (EVAP)
Fuel tank vapors flow through an in-line 2-way check valve from fuel tank to charcoal canister. Check valve maintains constant pressure in the fuel tank. When pressure exceeds specified pressure, fuel tank vapors flow to charcoal canister.
The main relay provides voltage to EVAP Canister Purge Control Solenoid (CPCS) when ignition is on. The ECM will ground the EVAP-CPCS when engine speed exceeds 1500 RPM, engine is at normal operating temperature and vehicle speed is above 15 MPH. EVAP-CPCS will open, allowing fuel vapors to be drawn from charcoal canister into the intake manifold.
POSITIVE CRANKCASE VENTILATION (PCV)
The PCV system circulates crankcase blow-by gases (hydrocarbons) into the air induction system rather than allowing them to escape to the atmosphere. Crankcase gases are mixed with air/fuel mixture. Crankcase ventilation system uses a PCV valve which prevents hydrocarbon fumes from collecting in intake manifold when engine is not running.
MALFUNCTION INDICATOR LIGHT (MIL)
Note. MIL is also known as the CHECK ENGINE light.
All vehicles are equipped with MIL, located on instrument panel. Light will glow when ignition is turned on and engine is not running. Light should go out when engine is started. When MIL remains on or flashes with engine running, the self-diagnostic system has detected a problem. If problem goes away, light will go out after 10 seconds, but a trouble code will remain stored in the ECM memory. For additional information, see TESTS W/CODES article in this section.