Description
ENGINE MANAGEMENT - 3.6Description
The ECU contains a microprocessor and discrete electronic component circuits that provide interfacing to peripheral input/output devices.
The microprocessor performs all system control functions and has a memory pre-loaded with system parameters that are accessed under software control. System response times are, therefore, reduced to a minimum and the system is rendered operational immediately the ignitiqn switch is set to position "II". System perhipherals are as follows:
1 Fuel injectors: solenoid actuated devices which spray quantities of fuel into the inlet manifold.
2 Ignition amplifer: an electronic device which, through the ignition coil, generates high energy electrical pulses for distribution to the sparking plugs.
3 Air flowmeter: a hot wire sensing device which monitors inlet manifold air flow for optimum fuelling and ignition control.
4 Idle speed control valve: a stepper motor driven device which controls the volume of air entering the engine to maintain a correct idle speed.
5 Crankshaft sensor: a device which generates engine speed and crankshaft position information for precise ignition timing and fuelling control.
6 Throttle potentiometer: a device which interprets the throttle position to identify idle, acceleration and full power demands.
7 Gearbox sensor: two linear gearbox selector actuated switches that induce idle speed corrections which compensate for engine load changes that occur when 'N' or 'P' is engaged or disengaged. On vehicles fitted with manual transmission units, the switch input to the ECU is connected to logic earth.
8 Fuel pump relay: a device which implements controlled fuel pump switching.
9 Coolant temperature sensor: a thermal device which monitors the coolant temperature to induce cold starting and warm-up enrichment.
10 Supplementary air valve: a solenoid actuated device which provides additional air during cold starting and warm-up at temperatures below-i 0'C.
11 Lambda sensor: a device which monitors the oxygen content of the exhaust to induce contamination corrections on vehicles exported to specified countries.
12 Air conditioning sensor: an air conditioning compressor clutch actuated switch that induces idle speed corrections which compensate for engine load changes that occur when the clutch is engaged or disengaged.
13 Air pump relay: a device which controls exhaust system air pump and solenoid vacuum valve operation on vehicles fitted with exhaust emmission control.
14 Idle fuel potentiometer: a device which provides fine adjustment of engine idle fuel. This device is set during vehicle manufacture and only requires adjustment when the air flowmeter assembly, of which it forms an integral part, is renewed.
Other system devices and communications are as follows:
1 Ignition 'on' sensing: an input taken from contact 87 of the ignition 'on' relay which, in addition to applying power to the ignition coil, energises the main and fuel pump relays through the ECU. A timer is also initiated which, through the fuel pump relay, permits fuel pump operation for approximately 0.5 seconds to ensure the fuel rail is pressurised prior to cranking.
2 Cranking sensing: an input which induces cranking enrichment when the starter solenoid is activated.
3 Battery voltage sensing: an input taken from contact 87 of the main relay which, in adddition to applying power to the supplementary air valve, air flowmeter, fuel injectors and both fuel and air pump relays, induces fuelling corrections that compensate for battery voltage fluctuations.
4 Idle override: an input derived from the instrumentation system which, in add itLon to displaying the vehicle road speed on the instrument pack, inhibits engine idle control at road speeds greater than 3 mph (4.8 kph).
5 VCM 1: an output applied to the instrumentation system to provide indication of an engine management system fault on the instrument pack.
6 VCM 2: a dual purpose output applied to the instrumentation system to (1) identify individual engine management system faults when the ignition switch is initially set to to position "II", and (2) provide precise fuelling conditions to the trip computer when the engine is running.