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11.2 - Overview of the Fuel Injection System ( )

The engine management system is controlled by the ECU and maintains optimum engine performance by metering the fuel into each cylinder's inlet tract and adjusting the ignition timing angle at the sparking plugs. It correlates data received from a number of sensors located on and around the engine to provide optimum ignition timing and fuel metering parameters relative to engine load and speed. The EM system also controls three features which may have a direct bearing on starting problems:-

1 Fuel pump - to prevent fuel flooding and/or spillage when the engine is stationary with the ignition switch in position 'II'.

2 Cold start control - to ensure there is sufficient fuel in the inlet manifold to create a combustible air/fuel mixture.

3 Idle speed control - to compensate for varying engine temperature and load conditions.

The system also incorporates a 'limp home" facility allowing continued engine operation following certain sensor failures, the specific failure being indicated on the instrument pack.

Fuel is delivered to solenoid operated injectors by the pump operating (via a variable pressure regulator) at virtually constant pressure so that the quantity of fuel injected for a given duration of injector on (open) time is constant.

Injector operation is by means of an electrical pulse which actuates a solenoid valve in the injector body. The duration of the pulse is determined by the ECU on intake air and engine speed information from the FLOWMETER and CRANKSHAFT SPEED SENSOR.

Correction factors are applied by the ECU to provide two functions which may cause starting problems:-

1 - Cranking enrichment during starting.
2 - Temperature enrichment during starting and warm-up.

Cranking enrichment occurs when the starter motor is activated by INCREASING THE INJECTOR OPERATING FREQUENCY FROM ONE PULSE TO THREE PULSES PER CRANKSHAFT REVOLUTION and is implemented by the ECU in response to an input from the STARTER SOLENOID. This cranking enrichment is only effective up to 600 rev/min.

Temperature enrichment occurs during starting (and warm up) by increasing the injector 'on' time and is implemented by the ECU in response to an input from the COOLANT TEMPERATURE SENSOR. This is the square topped sensor in the thermostat housing. After-start enrichment is provided to supply added fuel during warm up by the ECU which increases the injector 'on' time and decreases the amount of additional fuel supplied.

The ECU interfaces with input/output devices as follows:-

1 FUEL INJECTORS: solenoid actuated

2 IGNITION AMPLIFIER: generates high energy electrical pulses for distribution to the sparking plugs.

3 AIR FLOWMETER: a hot wire sensing device to monitor which inlet manifold air flow for optimum fuel and ignition control.

4 IDLE SPEED CONTROL VALVE: stepper motor driven device controlling the volume of air to maintain correct idle speed.

5 CRANKSHAFT SENSOR: provides engine speed and crankshaft position information to ECU for precise ignition timing and fueling control.

6 THROTTLE POTENTIOMETER: interprets the throttle position.

7 FUEL PUMP RELAY: controls fuel pump!

8 COOLANT TEMPERATURE SENSOR: thermal device which monitors coolant temperature to induce cold starting and warm-up enrichment.

9 SUPPLEMENTARY AIR VALVE: a solenoid actuated device to provide additional air during cold starting.

Other relevant system devices and signals 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.

The start routine is as follows:-

When the Ignition is switched 'On' power is applied to the various devices through contacts L14-87/30 of the main relay which is energised, via contacts B 17-87/30 of the ignition 'on' relay, when the vehicle ignition switch is in position '11', i.e. when 0 Volts is applied to B 17-85 of the ignition 'on' relay.

Power to the ECU at L3-1 and L2-10 generates a system reset which causes an initialization routine and starts the fuel pump to pressurise the fuel rail prior to cranking. The fuel pump is activated via contacts L5-87/30 of the fuel pump relay which is energised by an output from the ECU at L12-7.

Following the initialization routine, sensor scanning begins to determine engine conditions and to obtain appropriate ignition timing and fuel metering parameters. In addition, the following primary functions are performed:-

1 The stepper motor of the idle speed control valve is driven, via L12-15/16 and L12-18/19, 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 L12-20, to open the valve at temperatures below - 1O C. (If you're 14 hours from a Jaguar Dealer, it's either extremely hot or extremely cold)

3 Fuel pump operation is terminated, i.e. the output at L12-7 is removed, after approximately 0.5 seconds to eliminate possible fuel flooding should an injector be stuck in the open position.

4 The exhaust system air pump and solenoid vacuum valve (if fitted) are activated by the air pump relay which is energised, via L12-2, at temperatures between 15 C and 45 C.

When the engine cranks fuel pump operation is reinstated and any fault number displayed on the instrument pack fascia is deleted, provided the ECU detects crankshaft sensor input at L13-13 and 14.

As the engine rotates on the starter motor, fuel is introduced into the air flow of the inlet manifold by the fuel injectors which are actuated by the ECU under control of the crankshaft sensor input. Injector triggering occurs, through L12-12, 13 and 25, three times per crankshaft revolution with appropriate correction factors imposed. The ignition amplifier is also actuated at the correct times, through L12-1, to fire the sparking plugs.

When the engine fires, cranking enrichment stops at 600 rev/min, injector pulses occur once per rev, and both warm-up and after-start enrichment occur. 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.

Fuel and ignition requirements are calculated at each sensor scanning to maintain optimum engine efficiency. If a sensor failure is detected, a signal is sent to the instrument pack to indicate the failure. 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.


 

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This section currently maintained by Pascal Gademer; questions, comments, submissions and suggestions, email pascal@jag-lovers.org

 

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