Computers and Control Systems: Description and Operation
Component Locations - Powertrain Management:
INTRODUCTION
The electronic fuel injection system provides a reliable and efficient microprocessor controlled fuel management system.
The function of the system is to supply the exact amount of fuel directly into the inlet manifold according to the prevailing engine operating conditions.
To monitor these conditions, various sensors are fitted to the engine to measure engine parameters. Data from the sensors is received by the electronic control unit (ECU), the ECU will then determine the exact amount of fuel required at any condition.
The ECU having received data from the sensors produces pulses, the length of which will determine the simultaneous open time of each bank of injectors in turn, which will govern the amount of fuel injected.
DESCRIPTION
Electronic Control Unit--The electronic fuel injection system is controlled by the ECU which is located under the front right hand seat. The control unit is a microprocessor with integrated circuits and components mounted on printed circuit boards. The ECU is connected to the main harness by a 40 pin plug.
Injectors--The eight fuel injectors are fitted between the pressurized fuel rail and inlet manifold. Each injector comprises a solenoid operated needle valve with a movable plunger rigidly attached to the nozzle valve. When the solenoid is energized the plunger is attracted off its seat and allows pressurized fuel into the intake manifold.
Engine Coolant Temperature Sensor--The coolant sensor is located by the front left hand branch of the intake manifold. The sensor provides engine coolant information to the ECU. The ECU on receiving the signal from the sensor will lengthen slightly the time that the injectors are open, and reducing this time as the engine reaches normal operating temperature.
Fuel Temperature Sensor--The fuel temperature sensor is located in the fuel rail forward of the ram housing. The sensor sends fuel temperature data to the ECU. The ECU on receiving the data, will adjust the injector open time accordingly to produce good hot starting in high ambient temperatures.
Idle Air Control Valve (IACV)--The IACV is screwed into a housing attached to the rear of the plenum chamber, between the plenum chamber and bulkhead. The IACV has two windings which enable the motor to be energized in both directions thus opening or closing the air valve as required by the ECU.
The IACV will open and allow extra air into the plenum chamber to maintain engine idle speed when the engine is under increased (Electrical and Mechanical) loads.
The IACV will control engine idle speed when the vehicle is stationary.
Lambda Sensors (0xygen Sensors)--The two Lambda sensors are located forward of the catalysts mounted in the exhaust downpipes.
The sensors monitor the oxygen content of the exhaust gases and provide feedback information of the air/fuel ratio to the ECU. Each sensor is heated by an electrical element to improve its response time when the ignition is switched on.
Fuel Pressure Regulator--The fuel pressure regulator is mounted in the fuel rail at the rear of the plenum chamber. The regulator is a mechanical device controlled by plenum chamber vacuum, it ensures that fuel rail pressure is maintained at a constant pressure difference of 2.5 bar (36 psi) above that of the manifold. When pressure exceeds the regulator setting, excess fuel is returned to the fuel tank.
Fuel Pump--The electric fuel pump is located in the fuel tank and is a self priming wet pump. The motor is immersed in the fuel within the tank.
Air Flow Sensor--The hot-wire air flow sensor is mounted on a bracket attached to the left hand valance, rigidly connected to the air cleaner and by hose to the plenum chamber inlet neck.
The air flow sensor consists of a cast alloy body through which air flows. A proportion of this air flows through a bypass in which two wire elements are situated: one is a sensing wire and the other is a compensating wire. Under the control of an electronic module which is mounted on the air flow sensor body, a small current is passed through the sensing wire to produce a heating effect. The compensating wire is also connected to the module but is not heated, but reacts to the temperature of the air taken in, as engine intake air passes over the wires a cooling effect takes place.
The electronic module monitors the reaction of the wires in proportion to the air stream and provides output signals in proportion to the air mass flow rate which are compatible with the requirements of the ECU.
Throttle Potentiometer--The throttle potentiometer is mounted on the side of the plenum chamber inlet neck and is directly coupled to the throttle valve shaft.
The potentiometer is a resistive device supplied with a voltage from the ECU. Movement of the throttle pedal causes the throttle valve to open, thus rotating the wiper arm within the potentiometer which in turn varies the resistance in proportion to the valve position. The ECU lengthens the injector open time when it detects a change in output voltage (rising) from the potentiometer.
In addition the ECU will weaken the mixture when it detects the potentiometer output voltage is decreasing under deceleration and will shorten the length of time the injectors are open.
When the throttle is fully open, the ECU will detect the corresponding throttle potentiometer voltage and will apply full load enrichment. This is a fixed percentage and is independent of temperature. Full load enrichment is also achieved by adjusting the length of the injector open time.
When the throttle is closed, overrun fuel cut off or idle speed control may be facilitated dependant on other inputs to the ECU.
Road Speed Transducer--The road speed transducer is fitted between the upper and lower speedometer cables. It is mounted on a bracket located on the left hand chassis side member adjacent to the rear engine mounting. The transducer provides road speed data to the ECU. The ECU in turn detects vehicle movement from the road speed input and ensures that idle speed control mode is disengaged. Should the speed transducer fail in service the ECU idle speed control would become erratic.
Inertia Switch--The inertia switch is a mechanically operated switch located under the left hand front seat attached to the seat base rear cross-member.
The switch is normally closed and is in the ignition feed (fuse to fuel pump). In the event of a sudden impact the switch opens, and disconnects the electrical feed to the fuel pump. The switch is reset by pressing down the button.
Relays--The two electronic fuel injection relays are located under the front right hand seat mounted forward of the ECU. The main relay is energized via the ECU when the ignition is switched on and supplies current to the fuel injection system. The fuel pump relay is energized by the ECU which in turn operates the fuel pump to pressurize the fuel system.
EFI Warning Symbol (Instrument panel)--An EFI warning symbol incorporated into the instrument panel will illuminate when the ECU detects that it cannot maintain correct air/fuel ratio due to a fault in one of the following fuel injection system components:
- Air flow sensor
- Lambda sensor
- Water temperature sensor
- Throttle potentiometer
The symbol will illuminate on initial turn of the ignition key as part of the bulb check feature, and will go out after a few seconds.
If the symbol illuminates when the engine is idling or the vehicle is being driven, it indicates a failure of one of the four functions. The vehicle should be driven with care and the cause rectified. Refer to test procedure for the particular functions. Should one of the functions fail, the vehicle can still be driven due to a limp home feature incorporated into the fuel injection system.