PRE-RELEASE
Fuel system, description, E39
| Fuel system, description, E39 |
| Summary of the fuel system |
The fuel system is of an electronic, returnless, requirement-specific design. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reduction of the internal temperature of the fuel tank involves much fewer evaporation emissions.
An electric fuel pump of turbine type is mounted together with the fuel pump module inside the fuel tank. The fuel pump supplies fuel through the fuel pipe to the high pressure fuel pump. The high pressure fuel pump supplies fuel to a fuel rail with variable pressure.
The fuel is fed into the combustion chambers via precision manufactured fuel injectors with multiple holes. The high pressure fuel pump, the fuel rail pressure, the fuel injection setting and the duration of injection are controlled by the engine control module (ECM).
In BioPower engines, an ethanol sensor is mounted in the fuel pipe, before the high pressure fuel pump. The ethanol sensor measures the resistive and capacitive properties of the fuel to determine the ethanol content. This value is transmitted to the ECM as a frequency modulated signal.
The ECM adjusts the fuel injection amount with regard to the ethanol content in the fuel. The mixture is 14.7:1 for petrol and 9.8:1 for E85. The ignition position is also dependent on the ethanol content. In the event of an ethanol sensor fault, the ECM assumes a 40 per cent ethanol content as a set replacement value.
| Electronic returnless fuel system |
The electronic returnless fuel system is a microprocessor controlled fuel supply system which transports fuel from the tank to the fuel rail. This works as an electronic substitute for a traditional mechanical fuel pressure regulator. An overpressure valve inside the fuel tank provides further protection against overpressure.
| Control module, fuel pump flow |
The required fuel pressure is transmitted via a bus by the engine control module (ECM). The message is received by an SCM (Signal Conversion Module). The SCM controls a separate drive which supplies the pump with PWM. A fuel pressure sensor gives the feedback which the SCM required for fuel pressure control. In the event of a collision and airbag activation, the ACM will transmit a bus message which makes the ECM shut off the fuel pump.
| Fuel pressure sensor |
The fuel pressure sensor is a 5V, 3-pin unit which can be replaced. It is placed on the fuel line in front of the fuel tank. It is powered and earthed by the SCM. This sensor emits a fuel pressure signal to the SCM which is used to control the fuel pressure.
| Fuel tank |
The fuel is stored in the fuel tank. The tank is located in the rear of the car. The fuel tank is kept in place using two metal straps which are mounted on the underbody of the vehicle. The fuel tank is moulded from strong polyethylene.
| Fuel filler pipe |
The fuel filler pipe has a built-in limited to prevent leaded fuel being used.
| Fuel filler cap |
The fuel filler pipe has a threaded fuel filler cap. A torque limiter prevents the cap being tightened too hard. To fit the cap, turn it clockwise until you hear clear clicks. This indicates that the cap has been tightened sufficiently and is fully in place.
| Fuel pump unit |
An electric fuel pump of turbine type is mounted together with the fuel pump module inside the fuel tank. The pump is supplied with PWM from a separate drive which receives its commands from the SCM (Signal Conversion Module). The SCM receives information on the required pressure via a bus from the ECM and compares the value from the fuel pressure sensor.
The fuel pump supplies fuel through the fuel pipe to the high pressure fuel pump. The fuel pump module contains a check valve. The check valve maintains fuel pressure in the fuel pipe in order to prevent a long startup time.
The fuel pump module consists of the following main components:
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Fuel level sensor
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Fuel pump and reservoir
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Fuel filter
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Overpressure regulation valve
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| Tank sensor |
The fuel level sensor consists of a float, a float arm and a ceramic resistor card containing a variable resistor. This changes resistance in relation to the float arm position, which indicates the fuel level.
The engine control module (ECM) sends information on the fuel level to the high speed CAN bus to the body control module (BCM). This then transmits the fuel level percentage via the low speed CAN bus to the instrument panel in order to control the fuel gauge.
On four-wheel drive models, the ECM uses signal circuits in the primary tank sensor and the secondary tank sensor in order to calculate as a percentage how much fuel is remaining in the tank.
| Fuel pump |
The fuel pump is mounted in the fuel pump module's reservoir. The fuel pump is driven by an electric motor. The fuel is pumped to the high pressure fuel pump at a pressure which is based on the feedback from the fuel pressure sensor. The fuel pump emits a constant fuel flow even at a low fuel level and with an aggressive driving style. The flexible fuel pump pipe acts as a damper for fuel pulses and the noise generated by the fuel pump.
| Pressure release valve |
The overpressure valve replaces the ordinary pressure regulator which is used in mechanical returnless fuel systems. It is closed during normal operation. The overpressure valve is used in order to release pressure under overload, and it also acts as a pressure regulator if the fuel pump's drive locks to 100 per cent pulse width modulation (PWM) for the fuel pump.
Due to variations in the fuel system pressure, the overpressure valve's opening pressure is set to a higher value than that used for a pressure regulator in a mechanical returnless fuel system.
| Fuel lines made of nylon |
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Warning
The nylon pipes are designed to withstand the maximum pressure of the fuel system, to be exposed to fuel additives and to withstand temperature changes.
Heat resistant rubber hoses or corrugated plastic guides protect the parts of the pipes which are subject to chafing, high temperatures or vibration.
Nylon fuel pipes are partly flexible and they can be shaped in soft bends beneath the car. But if nylon pipes are forced into sharp bends, they will be folded and restrict the fuel flow. When they are exposed to fuel, the nylon pipe stiffen and fold more easily if they are bent too much. Take particular care when working on a car with nylon pipes.
| Quick couplings |
Quick couplings make it easier to fit and connect fuel system components. These couplings consist of a unique female coupling and a pipe end with a compatible male coupling. O-rings inside the female coupling constitute the fuel seal. Internal locking tabs inside the female coupling hold together the connections.
| Fuel pump, high pressure |
The high pressure fuel pump is of a mechanical 1-cylinder design which is driven by a cam with three lifters on the camshaft. The high pressure fuel is regulated by the high pressure fuel pump actuator, which is a part of the high pressure fuel pump.
Its actuator is made of up of a solenoid actuator which controls the inlet valve on the high pressure fuel pump. The ECM supplies battery voltage to the control element's positive control circuit and earth to the control element's negative control circuit. Both circuits are controlled via drives in the ECM. When deactivated, both drive elements will be deactivated and the inlet valve will be kept open by spring pressure.
When activated, the drive for the positive control circuit will power the high pressure pump actuator unit and the drive for the negative control circuit pulse width modulates (PWM) the circuit to earth. The ECM uses input data from the camshaft and the camshaft's position sensor to synchronise the actuator with the positions for each of the three cam lifters.
The ECM regulates the fuel pressure by adjusting the part of every pump stroke that supplies fuel to the fuel rail. The high pressure fuel pump also includes an integrated overpressure valve.
| Fuel distribution pipe |
The fuel rail fits on the top cover. The fuel rail distributes high pressure fuel to the injectors. The fuel rail consists of the following components:
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Direct injectors
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Fuel rail pressure sensor
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| Fuel injectors |
The fuel injection system is of a high pressure, direct injection, returnless and requirement-specific design. The injectors are fitted in the top cover under the intake ports and they inject fuel directly into the combustion chambers.
Direct injection requires a high fuel pressure due to the positioning of the injectors inside the combustion chambers. The fuel pressure must be higher than the compression pressure and this requires a high pressure fuel pump.
The injectors also require more electrical current due to the high fuel pressure. The ECM supplies a separate high voltage circuit and a high voltage control circuit for every injector. The injector's high pressure circuit and the high pressure control circuit are both controlled by the ECM.
The ECM powers the respective injectors by earthing the control circuit and controls each fuel injector with 65 V. This is controlled by a reinforcement capacitor in the ECM. During the 65 V phase, the capacitor is discharged via an injector, which causes the injector to open. It is then kept open with 12 V.
The injector is an internally opening electric solenoid valve and has six precision machined holes which generate a conical, oval spray pattern. The injector has a narrow, protruding tip to permit a sufficiently large cooling duct in the top cover.
| Fuel pressure sensor in the fuel rail |
The pressure sensor in the fuel rail detects the fuel pressure inside the fuel rail. The engine control module (ECM) supplies a 5 V reference voltage via the 5 V reference circuit and earths via the reference earth circuit. The ECM receives a varying signal voltage via the signal circuit. The ECM monitors the voltage in the fuel rail's pressure sensor circuits. When the fuel pressure is high, the signal voltage is high. When the fuel pressure is low, the signal voltage is low.
| Fuel pulsation damper |
The fuel pulse damper is part of the low pressure fuel pipe. The fuel pulse damper is diaphragm controlled, with fuel pump pressure on one side and spring pressure on the other side. The function of the damper is to damp the fuel pump's pressure pulses.
| Fuel measurement, operating modes |
The control module monitors the voltage from several sensors to determine how much fuel is to be supplied to the engine. The control module regulates the amount of fuel supplied to the engine by changing the injector pulse length. The fuel is supplied in one of several modes.
| Starting mode |
When the ignition is first switched ON, the SCM powers the fuel pump via the drive for two seconds. This allows the fuel pump to build up pressure in the fuel system. The control module calculates the fuel mixture on the basis of input data from the sensors for engine coolant temperature (ECT), absolute pressure (MAP), mass air flow (MAF) and throttle position. The system remains in starting mode until the engine speed reaches a predetermined level.
During a cold start, the ECM orders a double pulse mode under non lambda control in order to improve emissions during cold starting. In double pulse mode, the injectors are activated twice during each injection.
| Venting mode for flooding |
If the engine is flooded, the engine can be vented by holding down the accelerator fully while at the same time operating the starter motor. When the accelerator position sensor is fully depressed, the control module reduces the pulse length of the injector in order to make the fuel mixture leaner.
The control module maintains this injection setting as long as the accelerator is fully depressed and the engine speed is lower than a predetermined speed. If the accelerator is not fully depressed, the control module returns to starting mode.
| Driving mode |
Driving mode has two variants which are known as non lambda controlled and controlled. When the engine is first started and the engine speed is above a predetermined speed, the system starts to work without lambda control. The control module ignores the signal from the oxygen sensor (HO2S) and calculates the fuel mixture on the basis of input data from the sensors for engine coolant temperature (ECT), absolute pressure (MAP), mass air flow (MAF) and throttle position.
The system starts lambda control when the following conditions are met:
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HO2S has a varying output voltage, which shows that HO2S is sufficiently hot in order to operate correctly.
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The ECT sensor indicates that the temperature is above the limit.
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A certain amount of time has passed since the engine was started.
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There are specific values for the conditions above for each engine option, and these are stored in an EEPROM. Lambda control begins when these values have been reached. During lambda control, the engine control module calculates the fuel mixture, the activation time of the injectors, based on the signals from various sensors but mainly from HO2S. This makes it possible to maintain the fuel-air ratio very close to lambda 1.
| Acceleration mode |
When the drive depresses the accelerator, the air flow to the engine increases rapidly. To prevent any potential hesitation, the control module increases the pulse length of the injectors in order to add extra fuel during acceleration. This is also known as acceleration enrichment.
The control module determines how much fuel is required, based on the throttle valve position, engine coolant temperature (ECT), intake manifold pressure (MAP), mass air flow (MAF) and engine speed.
| Speed reduction mode |
When the driver releases the accelerator, the air flow to the engine is reduced. The control module monitors corresponding changes for the throttle valve position, the mass air flow (MAF) and the intake manifold pressure (MAP).
The control module shuts off the fuel completely if the speed reduction is very fast or takes place over a long period of time, e.g. under a relatively long period of engine braking on a downhill slope. The fuel is shut off in order to prevent damage to the catalytic converters.
| Correction mode for battery voltage |
When the battery voltage is low, the control module compensates for the weak spark supplied by the ignition system as follows:
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The fuel quantity increases
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Idling speed increases
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Ignition setting is increased
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| Fuel shutoff mode |
The control module shuts off the fuel from the injectors when the following conditions are met in order to protect the powertrain from damage and to improve driveability.
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The ignition is off. This prevents glow ignition.
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The ignition is ON but there is no ignition reference signal. This prevents flooding or backfiring.
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The engine speed is too high, over the red line.
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The speed of the car is too high, above the ratings for the tyres.
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During a long period of engine braking at high speed -- This reduces emissions and increases engine braking power.
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During a long period of speed reduction, in order to prevent damage to the catalytic converters.
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| Fuel adjustment |
The control module regulates the fuel mixture system in order to give the best possible combination of driveability, fuel economy and emissions control. It monitors the voltage signal of the heated oxygen sensor (HO2S) under lambda control and regulates the fuel supply by adjusting the injectors' pulse length on the basis of this signal.
The ideal fuel adjustment values are around 0 per cent for both short-term and long-term fuel adjustment.
A positive fuel adjustment value indicates that the control module is supplying fuel by increasing the pulse length in order to compensate for a lean ratio. A negative fuel adjustment value indicates that the control module is reducing the fuel quantity by reducing the pulse length in order to compensate for a rich ratio. A change in the fuel quantity will change the long-term and short-term fuel adjustment values.
The short-term fuel adjustment value changes quickly as a response to the HO2S signal voltage. These changes fine-tune the engine's fuel mixture.
The long-term fuel adjustment executes basic adjustment of the fuel mixture in order to zero and reset control of the short-term fuel adjustment.
A diagnostic tool can be used to monitor the short-term and long-term fuel adjustment values. The control module selects cells based on engine speed and load. If the control module detects a very lean or rich ratio, the control module will activate a diagnostic trouble code related to the fuel adjustment.
