INTRODUCTION
Note. This section covers the basic description and operation of engine performance related systems and components. Prior to diagnosing vehicles or systems with which you are not completely familiar, read through this section.
TURBOCHARGER
All models use a water-cooled turbocharger, mounted to the exhaust crossover pipe with a wastegate assembly attached to rear of turbine housing. The turbocharger consists of a turbine/compressor assembly, oil supply system and wastegate. Other components include impellers, impeller shaft, bearings and impeller housings.
The safety valve of the system is a pressure actuated wastegate that prevents excessive intake boost pressure. If boost pressure exceeds safe limits, engine damage may result. The wastegate opens when intake pressure exceeds a predetermined limit and allows exhaust gases to by-pass compressor.
Turbocharger operation requires a large quantity of clean oil to prevent bearing failure. Engine oil pressure provides constant lubrication to the system.
FUEL INJECTION
The electronic fuel injection systems, Multi-Point Fuel Injection (MPFI) and Single Point Fuel Injection (SPFI), supply optimum air/fuel mixture to engine under various operating conditions. This is determined through use of various sensors and a control unit. Amount of fuel injected is determined by duration of an electric pulse applied to fuel injector(s).
SPFI systems are a throttle body type, using a single fuel injector mounted in a throttle body atop an intake manifold. MPFI systems use a separate injector for each cylinder, mounted in intake manifold, next to intake valve.
The fuel injection control units, through various input sensors, determine fuel injection and the actuation of other output devices. Ignition spark timing is also controlled by the control unit.
The control units have built-in fail-safe mechanisms. If a fault occurs while driving, the control units will substitute pre-programmed values. Driving performance will be affected, but the vehicle may still be driven.
The control units have a self-diagnostic function which allows the unit to store a number of trouble codes in its memory. A Malfunction Indicator Lamp (MIL) informs the driver of system problems. An LED in the control unit will flash to indicate trouble code(s).
A/C Switch
Signals control unit of A/C compressor operation.
Airflow Meter
MPFI and SPFI systems employ a hot-wire type airflow meter. This 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.
Coolant Thermosensor
Coolant thermosensor is mounted on the waterpipe. This thermistor decreases resistance as coolant temperature increases. Thermosensor sends a coolant temperature signal to MPFI or SPFI control unit. Control unit uses this information to decide how much fuel to inject.
Crank Angle Sensor
Signals control unit of engine RPM and crank angle in reference to TDC.
EGR Temperature Sensor (SPFI California)
The EGR temperature sensor is located in EGR passage on intake manifold. An EGR temperature signal converted into resistance is transmitted to control unit for EGR system diagnosis.
Idle Switch
Signals control unit of closed throttle condition.
Knock Sensor (1.8L Turbo & 2.7L)
Knock sensor is installed on cylinder block, and senses knocking signals from each cylinder. If knocking occurs, a signal is transmitted to MPFI control unit. MPFI control unit retards spark timing to prevent engine knock.
Neutral & Parking Switches
Indicates transmission gear position.
Oxygen (O2) Sensor
The O2 sensor generates voltage according to the oxygen content within exhaust gases. The voltage created is greater when oxygen content is low (rich), and less when oxygen content is high (lean).
By sending this information to MPFI or SPFI control unit, air/fuel ratio of supplied mixture can be determined. Characteristics of voltage stabilize at temperatures of approximately 572-752° F (300-400° C).
Pressure Switches (1.8L Turbo)
Two positive pressure switches are located in front of body strut mount. One switch operates when intake manifold pressure reaches 1.0 psi (.07 kg/cm 2 ) and causes "TURBO" indicator light to illuminate.
At the same time, it also transmits heavy load signal to the control unit for canceling air/fuel ratio feedback control. The other switch operates at a pressure of 9.1 psi (.64 kg/cm 2 ) and cuts off fuel when an abnormal rise in turbocharging pressure occurs.
Throttle Position Sensor
Throttle position sensor contains both a potentiometer (variable resistor) and an idle switch. Throttle position sensor sends MPFI or SPFI control unit a potentiometer output signal corresponding to opening of throttle valve. Idle switch signal that occurs when throttle is nearly to idle position. Control unit uses these signals to control air/fuel ratio during acceleration, deceleration and idling.
Vehicle Speed Sensor
Vehicle speed sensor is located in speedometer and signals control unit of speed of vehicle.
OUTPUT SIGNALS - FUEL INJECTION
The MPFI and SPFI control units process information from the input sensors and sends appropriate voltage control signals to the following engine controls
- Air Control Valve (Emission)
- Air Regulator Control (Idle Speed)
- Auxilary Air Control Valve (1.8L MPFI - Idle Speed)
- By-Pass Air Control Valve (1.8L SPFI & 2.7L - Idle Speed)
- Canister Purge Control (CPC) Solenoid (Emission)
- "CHECK ENGINE" Light (Self-Diagnostics)
- Detonation (Knock) Sensor (1.8L Turbo & 2.7L - Timing)
- EGR Control Solenoid Valve (Emission)
- Exhaust Gas Sensor Heater Control (California - Emission)
- Fuel Injector(s) (Fuel Control)
- Fuel Pump Control (Fuel Delivery)
- Power Transistor & Ignition Coil (Ignition)
- Pressure Regulator Control Solenoid Valve (Fuel Delivery)
- Self-Diagnostics (Self-Diagnostics)
Fuel Pump
Fuel under pressure from electric fuel pump flows through a fuel damper, fuel filter, injector fuel rail and fuel pressure regulator. Fuel pump is located under body floor, in front of fuel tank. Electrical power for fuel pump operation during cranking mode is provided from starter relay via the fuel pump relay and MPFI or SPFI control unit. Fuel pressures for SPFI vehicles is 20-24 psi (1.4-1.7 kg/cm 2 ) and for MPFI vehicles is 26-30 psi (1.9-2.1 kg/cm 2 )
Fuel Pump Relay
MPFI or SPFI control unit turns on fuel pump relay based on inputs from the ignition switch and the 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, control unit provides fuel pump relay ground. This activates fuel pump.
Fuel Pressure Regulator
Fuel is fed to fuel chamber through fuel inlet connected with injector. A difference in pressure between fuel chamber and spring chamber causes diaphragm to be pushed down, and fuel is returned to fuel tank through return line.
The electronic fuel injection systems, Multi-Point Fuel Injection (MPFI) and Single Point Fuel Injection (SPFI), supply optimum air/fuel mixture to engine under various operating conditions. This is determined through use of various sensors and a control unit. Amount of fuel injected is determined by duration of an electric pulse applied to fuel injector(s).
SPFI systems are a throttle body type, using a single fuel injector mounted in a throttle body atop an intake manifold. MPFI systems use a separate injector for each cylinder, mounted in intake manifold, next to intake valve.
Auxiliary Air Valve (MPFI 1.8L)
Auxiliary air valve is used to increase airflow when engine is started at a low ambient temperature. It consists of a coiled bi-metallic spring, a shutter valve, and an electric heater element.
Airflow is increased as temperature becomes lower. Current to heater is supplied by fuel pump relay circuit. Shutter valve turns gradually to decrease airflow.
By-Pass Air Control System (SPFI)
An air passage by-passing throttle valve is provided to route air directly into lower course of throttle valve. By-pass air control valve is located in middle of air passage.
By-pass air control valve controls amount of air at engine starting, idle speed, etc. By-pass air control valve is driven by signals from SPFI control unit and regulates opening of by-pass air to maintain idle speed at set value.
By-Pass Air Control Valve (MPFI 2.7L)
By-pass air control valve is controlled by ECU to allow air to by-pass throttle valve. This allows engine to operate at optimum speed under various conditions. By-pass air control valve consists of a reversible DC motor connected to an air control valve. Air control is achieved by rotating valve until desired engine RPM is obtained.
Fast Idle Solenoid (MPFI 1.8L)
To compensate for decrease in idle speed during A/C operation, fast idle solenoid activates to open idle by-pass passage in throttle body. Fast idle RPM can be adjusted by turning the fast idle adjusting screw.
The ignition system consists of a distributor containing a crank-angle sensor, rotor plate, Light Emitting Diode (LED), photo diode and the wave forming circuit, an ignition coil equipped with a power transistor, and MPFI or SPFI control unit. The crank-angle signal and reference signal detected by crank-angle sensor are sent to MPFI or SPFI control unit.
The control unit determines optimum ignition timing from these signals and other engine operating parameters. It then transmits an ignition signal to ignition coil ignitor. The ignitor amplifies this ignition signal and causes primary current to trigger in ignition coil.
Ignition Timing Advance Control
All models have ignition spark timing controlled by the EFC, MPFI or SPFI control unit. Ignition system controls ignition timing to a precise point by matching the vehicles operating conditions to pre-programmed timing advance and retard specifications.
These parameters are stored in the memory circuits of the control unit. The control unit compares the incoming voltage signals from monitoring sensors to these parameters and adjusts the timing and other output signals accordingly.
Detonation Retard Operation (1.8L Turbo & 2.7L)
When engine knock (pre-ignition) is present, a signal is generated by knock sensor and is sent to MPFI control unit. The MPFI control unit then retards spark timing until engine knocking stops. Control unit will then gradually advance spark timing.
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, 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) CONTROL
To lower oxides of nitrogen (NOx) exhaust gas emissions, a computer controlled exhaust gas recirculation system is used. EGR introduces exhaust gases back into intake system. Exhaust gases lower peak combustion temperatures, which lowers NOx emissions down. All EGR valves receive operating vacuum from EGR control solenoid valve.
Fuel Injected (Non-Turbo)
Vapor from expanding fuel in fuel tank collects in expansion tank. Vapor flows from expansion tank and into charcoal canister through vapor separator and 2-way valve. Intake manifold vacuum controls canister purge control solenoid on canister. When purge control solenoid is opened, vapor flows from canister into throttle body.
Fuel Injected (Turbo)
Fuel travels from fuel tank to canister in same manner as fuel injected non-turbo models with 2 exceptions. When turbo is in effect, canister purge control valve is closed by a return spring. Also, an additional purge line purges vapor into air intake boots when engine is running.
POSITIVE CRANKCASE VENTILATION (PCV)
PCV system consists of following: PCV valve and connecting hoses. PCV system draws crankcase blow-by, vapors and gases into combustion system rather than allowing it to escape to atmosphere. Crankcase gases mix with air/fuel mixture and are burned in combustion chamber. Crankcase ventilation system uses a PCV valve. It is basically a one-way check valve, held closed by spring pressure when engine is not running. This prevents hydrocarbon fumes from collecting in intake manifold which can result in hard starting.
When engine is running, manifold vacuum pulls PCV valve open allowing crankcase fumes to enter intake manifold. If engine backfires through intake manifold, PCV valve closes and stops any flow of gases. This prevents ignition of fumes in crankcase.
CHECK ENGINE LIGHT
All vehicles are equipped with a "Check Engine" light located on instrument panel. Light will illuminate when ignition switch is turned to "ON" position (bulb check) and when systems related to emission controls are malfunctioning during normal operation. Trouble code will be displayed on O2 monitor light through a flashing code.