Operation
ENGINE MANAGEMENT - 3.6OPERATION
A circuit diagram of the engine management system detailing interconnections between the ECU and the various input/output pheripheral devices is shown in Figure 4.
Ignition On
Power is applied to the various devices through contacts LI4-87/30 of the main relay which is energised, via contacts B17-87/30 of the ignition 'on' relay, when the vehicle ignition switch is in position "II", i.e. when 0 Volts is applied to B17-85 of the ignition 'on' relay.
Application of power to the ECU at LI3-1 and LI2-10 generates a system reset which causes the microprocessor to perform an initialization routine (a sofware program stored in memory}, condition input circuits for sensor scanning and initiates fuel pump operation to pressurise the fuel rail prior to cranking. The fuel pump is activated via contacts LI5-87/30 of the fuel pump relay which is energised by an output from the ECU at LI2-7.
On completion of the initialization routine, sensor scanning commences and analogue information from the sensors is converted into digital data for storage. The data thus stored is then evaluated to determine prevailing engine conditions and memory locations are accessed to obtain appropriate ignition timing and fuel metering parameters. In addition, the following functions are performed:
1 The stepper motor of the idle speed control valve is driven, via LI2-15/16 and LI2-18/19, to set the valve at a position suitable for engine starting. Rapid valve positioning is achieved for all conditions by extending or retracting its stem from a mid-travel position restored each time the ignition switch is set to "off".
2 The solenoid of the supplementary air valve is actuated, via LI2-20, to open the valve at temperatures below -10°C.
3 Fuel pump operation is terminated, i.e. the output at LI2-7 is removed, after approximately 0.5 seconds to eliminate possible fuel flooding should an injector be stuck in the open position. This feature is also used to eliminate possible fuel spillage creating a hazardous condition at an accident scene if fuel line fracture occurs due to impact damage.
4 The exhaust system air pump and solenoid vacuum valve (if fitted) are activated by the air pump relay which is energised, via LI2-2, at temperatures between 15°C and 45°C.
5 A number relating to a fault which may have occurred during the last period that the engine was run is recalled from memory and displayed on the instrument pack fascia.
6 A breather pipe heater is actuated, via a breather pipe heater relay, under the control of a screenwash jet heater sensor.
Engine Cranking
Fuel pump operation is reinstated and any fault number displayed on the instrument pack fascia is erased when the engine is cranked, provided that the ECU detects a crankshaft sensor input at LI3-13 and 14. The Lambda sensor heater is also activated to heat the sensor on vehicles fitted with exhaust emission control.
As the engine rotates under the influence of the starter motor, fuel is introduced into the air flow of the inlet manifold by the fuel injectors which are actuated by the FCU under control of the crankshaft sensor input. Injector triggering occurs, through LI2-12, 13 and 25, three times per crankshaft revolution with appropriate correction factors imposed. The ignition amplifier is also actuated at the correct times, through LI2-1, to fire the sparking plugs.
Engine Running
When the engine starts, cranking enrichment is terminated at 600 rev/min, i.e. injector pulses occur once per crankshaft revolution, and both warm-up and after-start enrichment is imposed. In addition, any extra manifold air is delivered by the supplementary air valve which is driven in response to coolant temperature, throttle potentiometer and crankshaft sensor inputs.
The engine idle speed is controlled, through LI2-15/16 and LI2-18/19, by the ECU which drives the idle speed control valve stepper motor from coolant temperature, throttle position and crankshaft speed information. Compensation is also provided for fluctuating engine load by monitoring air conditioning clutch and gearbox (automatic only) sensor inputs at LI3-21 and 3 respectively. The engine idle speeds are set as follows:
1. Cold in neutral - 800 rev/min.
2. Hot in neutral - 700 rev/min.
3. Cold in drive - 650 rev/min.
4. Hot in drive - 580 rev/min.
If the supplementary air valve is deployed, i.e. temperature below -10°C, the idle speed control valve intercepts the engine speed on supplementary air valve closure. This ensures that the desired engine idle speed is maintained without searching.
Fuel and ignition requirements are calculated at each sensor scanning to maintain optimum engine efficiency over its entire range, including full power and acceleration demands. Should a sensor failure be detected, an output is applied to the instrument pack to provide indication of the failure on the fascia. The nature of the fault is also stored in ECU memory and is output as a fault number the next time the ignition switch is set to position "II".
Exhaust emission regulation is implemented by the ECU under control of the Lambda sensor (if fitted) which monitors the oxygen content of the exhaust system and provides a corresponding signal to the ECU at LI3-17. This signal imposes corrections on the basic injector 'on' times to reduce exhaust emissions to a minimum. Power to the Lambda sensor heater is supplied from contact LI5-87/30 of the fuel pump relay and, therefore, exhaust emission control is only operational during periods that fuel pump operation is permitted.
Additional air is introduced into the exhaust system by a relay actuated air pump and solenoid vacuum valve (if fitted) to reduce the density of the gases emitted, the relay being actuated by an output from the ECU at LI2-2.
NOTE: During periods that the air pump is operating, Lambda sensor operation is inhibited.
Fault identification:
Definitions of fault numbers displayed on the instrument pack fascia are as follows:
1 Cranking signal failure: no crankshaft sensor signal detected after cranking for 6 seconds, or the cranking signal line at LI2-8 is active above 2000 rev/min.
2 Air flowmeter failure: either open-circuit or short-circuit to ground.
3 Coolant temperature sensor failure.
4 Feedback circuit failure (Catalyst Vehicles).
5 Air flowmeter failure: low throttle potentiometer voltage with high air flowmeter voltage.
6 Air flowmeter failure: high throttle potentiometer voltage with low air flowmeter voltage.
7 Idle fuel adjustment potentiometer failure.
8 Not allocated: should this fault number be displayed, a 6.8 kilohm resistor fitted in place of a hot start sensor is faulty.