Fuel Management: Notes
Fuel Tank: The fuel tank is made of high density polyethylene (reduced weight) which is manufactured to meet safety requirements.
A "saddle" type tank is used which provides a tunnel for the driveshaft but creates two separate low spots in the tank.
A Syphon jet is required with this type of tank to transfer fuel from the left side, linked to the fuel return line.
As fuel moves through the return, the siphon jet creates a low pressure (suction) to pick up fuel from the left side of the tank and transfer it to the right side at the fuel pick up.
Fuel Pump: The electric fuel pump supplies constant fuel volume to the injection system. This system uses a single submersible (in the fuel tank) pump. The inlet is protected by a mesh screen.
When the fuel pump is powered, the armature will rotate the impeller disk creating low pressure at the inlet. The fuel will be drawn into the inlet and passed through the fuel pump housing (around the armature). The fuel lubricates and cools the internals of the pump motor.
The fuel will exit through a non-return check valve to supply the injection system. The non-return check valve is opened by fuel exiting the pump and will close when the pump is deactivated. This maintains a "prime" of fuel in the filter, lines, hoses and fuel rail.
The pump contains an internal overpressure relief valve that will open (reducing roller cell pressure) if there is a restriction in the fuel supply hardware.
Fuel Supply Hardware: The fuel is transferred from the fuel pump to the fuel filter then on to the fuel rail. This is accomplished by a combination of steel lines (2) and high pressure hoses (1).
The fuel pump delivers more volume than the injection system requires. The unused fuel is routed through a return line to the tank. The fuel is constantly circulated in this manner.
The fuel filter "traps" contaminants before they reach the fuel injectors and should be replaced at the specified interval. The arrow (on the filter) denotes the installation direction. The large filter size also serves as a volume reservoir for pressurized fuel (dampening fuel pump pulsations).
The fuel rail distributes an even supply of fuel to all of the injectors, and also serves as a volume reservoir.
Fuel Pressure Regulator: The Fuel Pressure Regulator maintains a constant "pressure differential" for the fuel injectors.
The fuel pressure is set to 3.0 bar (+/- 0.2) by internal spring tension on the restriction valve.
The vacuum chamber is sealed off by a diaphragm which is connected by a hose to the intake manifold. Intake manifold vacuum regulates the fuel pressure by assisting to compress the spring (lowering fuel pressure).
When the restriction valve opens, unused fuel returns back to the fuel tank.
Examples of "pressure differential" are:
- At low to part throttle, intake manifold vacuum is available at the tip of the fuel injectors to enhance fuel "flow through". Vacuum is also applied to the fuel pressure regulator vacuum chamber, causing the diaphragm to compress the spring which opens the restriction valve. This lowers the fuel pressure available to the fuel injectors.
- Wide open throttle depletes intake manifold vacuum at the tip of the fuel injectors and in the fuel pressure regulator vacuum chamber. The spring closes the restriction valve to raise fuel pressure available to the fuel injectors. This maintains pressure differential (fuel flow through) for the fuel injectors.
By maintaining constant Fuel Pressure Differential through vacuum sensing (engine load), the ECM can then regulate volume and mixture by the length of time the injectors are open (duration).
The Fuel Pressure Regulator is mounted on the fuel rail (arrow).
Bosch Fuel Injectors: The Fuel Injectors are electronically controlled solenoid valves that provide precise metered and atomized fuel into the engine intake ports. The Fuel Injector Valve consists of:
- Fuel Strainer
- Electrical Connector
- Solenoid Winding
- Closing Spring
- Solenoid Armature
- Needle Valve
- Pintle
Fuel is supplied from the fuel rail to the injector body. The fuel is channeled through the injector body to the needle valve and seat at the tip of the injector.
Without electrical current, the needle valve is sprung closed against the seat.
The Fuel Injectors receive voltage from the Engine Control Module Relay. The ECM activates current flow through the injector solenoid creating a magnetic field that pulls the needle "up" off of its seat.
The pressurized fuel flows through the opening and deflects off of the pintle.
The pintle (tip of the needle) is a cone shaped deflector that "fans out" the fuel spray into an angled pattern which helps to atomize the fuel.
When the ECM deactivates current flow, the needle valve is sprung closed against the seat and fuel flow through the injector is stopped.
The length of time that the ECM activates the Fuel Injectors is very brief, the duration is in milli-seconds (ms). This affects the mount of fuel volume flowing through the Fuel Injectors.
The ECM will vary the length of time (ms) to regulate the air/fuel ratio (mixture).
The Fuel Injectors are mounted in rubber "o rings" between the fuel rail and the intake manifold to insulate them from heat and vibration. This insulation also reduces the injector noise from being transmitted through the engine compartment. The Fuel Injectors are held to the fuel rail by securing clips (arrow).
If a Fuel Injector is faulty (mechanical or electrical), it can produce the following complaints:
- "CHECK ENGINE" Light
- Excessive Tailpipe Smoke (leaking)
- Engine Hydrolock (leaking)
- Oxygen Sensor/Mixture/Injector Related Fault Codes
- Misfire/Rough Idle (Leaking or Blocked)
- Long Crank Time (leaking)
Air Shroud Injector: To comply with emission regulations, Air Shrouded Injectors have been fitted on the M42 engine since 1994 MY. There is an air gap between the inner and outer body of the fuel injector which allows additional metered air to be drawn in. This air disperses and mixes with the injected fuel which improves fuel atomization as it enters the combustion chamber thus lowering CO/HC emissions.
The Air Shrouded Injectors incorporate a hose fitting on the outer injector body which connects each injector via a rubber hose, to the molded Idle Speed Control Valve hose, under the intake manifold.
The metered air is taken from a fitting located in the intake bellows boot in front of the throttle valve (ported vacuum). The system is self regulating with greater air flow at idle and low load engine ranges (intake manifold vacuum drawing air in).
The Air Shrouded supply components are:
- Idle Speed Control Valve
- Connection to Intake Bellows Boot
- Connection to Intake Manifold
- Hoses for Air Shrouded Injectors
Crankshaft Position/RPM Sensor: This sensor provides the crankshaft position and engine speed (RPM) signal to the ECM for Fuel Pump and Injector operation. This is an inductive pulse type sensor. The ECM provides the power supply to this component.
The sensor scans an incremental impulse/gear wheel that has a total of 58 teeth and a gap of two missing teeth. The rotation of the impulse wheel generates an A/C voltage signal in the sensor where-by each tooth of the wheel produces one pulse. The ECM counts the pulses and determines engine RPM.
The gap of two missing teeth provides a reference point that the ECM recognizes as crankshaft position.
The impulse wheel is mounted behind the crankshaft pulley. The Sensor is mounted on the front timing cover (housing).
A fault with this input will produce the following complaints:
- No Start
- Intermittent Misfire / Driveability
- Engine Stalling
Camshaft Position Sensor (Cylinder Identification): The cylinder ID sensor (inductive pulse) input allows the ECM to determine camshaft position in relation to crankshaft position. It is used by the ECM to establish the firing order for the direct ignition system and the semi-sequential fuel injection timing.
The sensor scans a tooth mounted on the intake camshaft drive gear (mounted in the front of the cylinder head). The ECM provides the power supply for this component and monitors the A/C voltage generated when the tooth passes the sensor tip. This input provides one pulse per revolution of the camshaft.
This input is only checked by the ECM during "start up". The camshaft position is referenced to the crankshaft position, and is not monitored until the next engine start up.
If the ECM detects a fault with the Cylinder ID Sensor, the "CHECK ENGINE " Light will be illuminated and the system will still operate based on the Crankshaft Position/RPM Sensor. Upon a restart, a slight change in driveability could occur because the ECM will activate Parallel Fuel Injection, all of the injectors will be activated at the same time.
Engine Coolant Temperature: The Engine Coolant Temperature is provided to the ECM from a Negative Temperature Coefficient (NTC) type sensor. The ECM determines the correct fuel mixture and base ignition timing required for the engine temperature.
The sensor decreases in resistance as the temperature rises and vice versa.
The ECM monitors an applied voltage to the sensor (5v). This voltage will vary (0-5v) as coolant temperature changes the resistance value.
This sensor is located in the coolant jacket of the cylinder head (1).
If the Coolant Temperature Sensor input is faulty, the "CHECK ENGINE" Light will be illuminated and the ECM will assume a substitute value (80° C) to maintain engine operation.
Throttle Position Sensor: The potentiometer is monitored by the ECM for throttle angle position and rate of movement. For details about the sensor, refer to the AIR MANAGEMENT section.
As the throttle is opened, the ECM will increase the volume of fuel injected into the engine. As the throttle plate is closed, the ECM activates fuel shut off if the RPM is above idle speed (coasting).
If the Throttle Position input is defective, a fault code will be set and the "CHECK ENGINE" Light will illuminate. The ECM will maintain fuel injection operation based on the Air Flow Volume Sensor and the Crankshaft Position/RPM Sensor.
Air Flow Volume Sensor: This potentiometer sends a signal to the ECM representing the measured amount of intake air volume. This input is used by the ECM to determine the amount of fuel to be injected for correct air/fuel ratio. For details about the sensor, refer to the AIR MANAGEMENT section.
If this input is defective, a fault code will be set and the "CHECK ENGINE" Light will illuminate. The ECM will maintain fuel injection operation based on the Throttle Position Sensor and Crankshaft Position/RPM Sensor.
Air Temperature: This signal allows the ECM to make a calculation of air density. The sensor is located in front of the measuring flap. For details about the sensor, refer to the AIR MANAGEMENT section.
The varying voltage input from the NTC sensor indicates the larger proportion of oxygen found in cold air, as compared to less oxygen found in warmer air. The ECM will adjust the amount of injected fuel because the quality of combustion depends on oxygen sensing ratio.
If this input is defective, a fault code will be set and the "CHECK ENGINE" Light will illuminate.