AIR INDUCTION SYSTEM
All engines use the same basic air induction system. Remote air filter (with airflow sensor) is ducted to a plenum-mounted throttle body.
COMPUTERIZED ENGINE CONTROLS
Accent uses a Sequential Fuel Injection (SFI) system. This is a computerized emission, fuel, and ignition system. The Electronic Control Module (ECM) determines at which point each injector supplies fuel. The SFI system controls air/fuel ratio, ignition timing, Idle Air Control (IAC), fuel pressure, and purge control.
ELECTRONIC CONTROL MODULE (ECM)
The ECM receives and processes signals from data sensors and switches to control fuel delivery. Fuel delivery time is modified for operating conditions such as cold starting, altitude, acceleration, and deceleration.
Note. Components are grouped into 2 categories. First category is INPUT DEVICES, which are components that control or produce signals monitored by the ECM. The second category is OUTPUT SIGNALS, which are components controlled by the ECM.
INPUT DEVICES
The ECM controls various output devices based upon signals received from input devices. These devices include sensors, switches, and circuits such as an RPM reference signal from the ignition coil. 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 section. Available input signals include
A/C Switch
When the air conditioner is turned on, a signal is sent to the ECM. The ECM then adjusts the Idle Air Control (IAC) servo to maintain optimum idle speed.
Acceleration/Rough Road Sensor
This sensor is located on bracket, on right front strut tower. When driving on rough road condition, ECM uses the accelerator sensor input signal to avoid the wrong misfire detection.
Camshaft Position Sensor
The Camshaft Position (CMP) sensor senses TDC point of cylinder No. 1 in its compression stroke. This signal is fed to ECM to determine sequence of fuel injection.
Crankshaft Position Sensor
The Crankshaft Position (CKP) sensor is located near the flywheel. Voltage from the CKP sensor is provided to the ECM for detecting engine RPM and crankshaft position.
Engine Coolant Temperature (ECT) Sensor
The ECT sensor is a thermistor whose resistance decreases as coolant temperature increases. The ECM uses coolant temperature information for controlling fuel enrichment when engine is cold. ECT sensor is located on thermostat housing.
Heated Oxygen Sensor (HO2S)
All vehicles are equipped with dual oxygen sensors; a second sensor is installed between the catalytic converter and muffler. HO2S determines oxygen content of exhaust gases and produces a voltage depending on concentration of oxygen. Output voltage of the sensor ranges from zero volts (lean) to about one volt (rich). The ECM monitors this sensor signal to control fuel delivery time.
Intake Air Temperature Sensor
The Intake Air Temperature (IAT) sensor is located in air cleaner housing. This sensor is a thermistor which measures temperature of incoming air, and sends a signal to the ECM. The ECM uses air temperature sensor information for controlling fuel delivery.
Knock Sensor (KS)
Knock sensor is mounted on engine block. Sensor detects knocking condition/vibration from engine. The piezo electric element converts this vibration into a voltage signal to the ECM. If engine knocking occurs, ECM retards timing to suppress knock.
Mass Airflow (MAF) Sensor
MAF is a hot film type airflow sensor, and is mounted within the intake duct between the air cleaner and throttle body. Mass airflow rate is measured by detection of heat transfer from a hot film probe.
Mass airflow sensor generates a pulse so it repeatedly opens and closes between the 5-volt pulses supplied from the ECM. This results in the change of the temperature of the hot film probe and in the resistance. The ECM uses this signal to determine basic fuel injection duration.
Power Steering Pressure (PSP) Switch
The PSP switch closes in response to an increase in power steering fluid pressure (load condition). With the switch closed, a circuit from the ECM to vehicle ground is completed. The ECM sends a signal to the IAC motor to adjust idle speed to compensate for increased engine load.
Throttle Position (TP) Sensor
The TP sensor is a potentiometer connected to the throttle valve shaft. As throttle opening changes, the sensor sends a voltage signal to ECM. The ECM uses this signal to calculate fuel injection duration.
Transaxle Range Switch (A/T Models)
The Transaxle Range (TR) switch informs the ECM whenever the transaxle is in Neutral or Park. ECM determines automatic transmission load, and signals the Idle Air Control (IAC) servo to maintain optimum idle speed.
Vehicle Speed Sensor (VSS)
The Vehicle Speed Sensor (VSS), located within the speedometer assembly, uses a reed switch to sense speedometer gear revolutions. The VSS converts speedometer gear revolution (vehicle speed) into pulse signals which are sent to the ECM.
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 system indicated after component.
The ECM processes information from input sensors and sends appropriate control signals to the following engine controls
A/C Clutch
See MISCELLANEOUS CONTROLS .
EGR Control Solenoid Valve
See EXHAUST GAS RECIRCULATION (EGR) CONTROL under EMISSION SYSTEMS.
Fuel Injectors
See FUEL CONTROL under FUEL SYSTEM.
Fuel Pump Relay
See FUEL DELIVERY under FUEL SYSTEM.
Idle Speed Control (ISC) Actuator
See IDLE SPEED under FUEL SYSTEM.
Malfunction Indicator Light (MIL)
See MALFUNCTION INDICATOR LIGHT under SELF-DIAGNOSTIC SYSTEM.
Power Transistor
See IGNITION SYSTEM .
Purge Control Solenoid
See EVAPORATIVE CONTROL under EMISSION SYSTEMS.
Self-Diagnostics
See SELF-DIAGNOSTIC SYSTEM .
SFI Control Relay
See RELAYS in SYSTEM/COMPONENT TESTS article.
FUEL DELIVERY
Fuel is pumped through an in-tank filter by an electric fuel pump located within the fuel tank. Passing through a second filter, fuel is maintained at a constant pressure for the injectors by the fuel pump and pressure regulator.
Fuel Pump
Located within fuel tank, the fuel pump consists of an impeller driven by a DC motor. The pump has an internal check valve (to maintain system pressure) and a relief valve.
Fuel Pressure Regulator
The fuel pressure regulator, located on the fuel delivery pipe, maintains a constant pressure at the injectors during all engine operating conditions.
This relay is located either at the left side of driver-side console or right side of passenger-side console. This multipurpose relay switches power to the following vehicle sensors and actuators: airflow sensor, idle speed control, injectors, and fuel pump. For specific system configuration, see WIRING DIAGRAMS section.
Fuel is supplied to engine through electronically pulsed (timed) fuel injectors. The ECM controls amount of fuel metered through injectors based on information received from various sensors.
The ISC actuator is a double coil type. The 2 coils are driven by separate driver stages in the ECM. Depending on the pulse duty factor, the equilibrium of the magnetic forces of the 2 coils will result in different angles of the motor. Actuator is located on by-pass hose to throttle body.
Idle control increases idle speed when power steering oil pressure switch or A/C switch is activated, or when transmission is shifted from Neutral to Drive (A/T). During deceleration, the IAC motor delays closing of throttle valve to its normal idling position.
DIRECT IGNITION SYSTEM (DIS)
DIS is a molded dual-coil system that supplies energy for ignition at high speeds. System does not use a distributor. Electronic Control Module (ECM) directly activates power transistor for ignition timing control.
When ignition is turned on, battery voltage is applied to ignition coil primary winding. As the crankshaft position sensor shaft rotates, ignition signals are transmitted from the ECM to the power transistor. These signals activate the power transistor, which switches primary current on and off. This action produces high voltage in the secondary winding of the ignition coil.
IGNITION TIMING CONTROL SYSTEM
The ECM controls ignition timing, based on signals from various engine sensors. Optimum ignition timing is determined by making corrections for engine coolant temperature, intake air temperature, and other engine operating conditions.
EVAPORATIVE CONTROL
The system consists of a vacuum relief filler cap, overfill limiter (2-way valve), fuel check valve, charcoal canister, purge control valve, and connecting lines and hoses.
With ignition off, fuel vapors are vented into charcoal canister. When engine is at normal operating temperature and engine speed is greater than idle, a thermovalve opens and allows vacuum to open the purge control valve. Canister vapors are then drawn into the intake manifold for burning through purge control valve. The purge control valve is kept closed during idle and engine warm-up to reduce HC and CO emissions.
POSITIVE CRANKCASE VENTILATION (PCV) VALVE
The positive crankcase ventilation system consists of a PCV valve and ventilation hoses. The PCV valve is located on the valve cover. When the engine is running, manifold vacuum pulls the PCV valve open, allowing crankcase fumes to enter intake manifold. If the engine backfires through intake manifold, the PCV valve closes to prevent crankcase combustion.
MALFUNCTION INDICATOR LIGHT
Note. ECM diagnostic memory is kept alive by direct power supply from the battery. Memory will be erased if battery or ECM is disconnected.
The Malfunction Indicator Light (MIL) will illuminate for several seconds when the ignition is first turned on. It remains illuminated for several seconds after engine has started. If an abnormal input signal from a sensor occurs, the MIL will illuminate and a DTC will be stored in ECM memory. For additional information, see TESTS W/CODES article.
MISCELLANEOUS CONTROLS
Note. Although not considered true engine performance-related systems, controlled devices may affect driveability if they malfunction.
When A/C is turned on while engine is at idle, IAC servo is commanded to increase idle speed. To prevent A/C compressor clutch from switching on before idle speed has increased, the ECM briefly opens the A/C relay circuit.
