Fuel Management: Notes
Fuel Tank: The fuel tank is made of high density polyethylene (reduced weight) which is manufactured to meet safety requirements.
A mid-chassis mounted "saddle" type tank is used (E36/ E39) which provides a tunnel for the driveshaft but creates two separate low spots in the tank.
A Siphon 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.
The Z3 uses a conventional type fuel tank that is mounted between the seats and the luggage compartment. The Z3 has a single sending unit that (with the fuel pump) is accessed from behind the passenger seat.
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 disc 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 Components: The fuel is transferred from the fuel pump to the fuel filter. 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 (under the driver side floor). The large filter size also serves as a volume reservoir for pressurized fuel (dampening fuel pump pulsations).
Running Losses refers to the fuel vapors that can escape to the atmosphere during vehicle operation. The fuel pump delivers more volume than the injection system requires. The unused fuel is routed through a return line to the tank at the fuel pressure regulator integrated in the Running Losses 3/2 Way Valve under the driver side floor. The fuel is constantly circulated in this manner.
Using the by-pass type regulator reduces the returned fuel temperature to the tank.
Running Losses Fuel Supply: The ECM controls the operation of the Running Losses Fuel Circuit by activating the by-pass solenoid. The solenoid is energized for 20 seconds on engine start up to supply full fuel volume to the fuel rail. After 20 seconds, the solenoid is deactivated and sprung closed (the by-pass is opened). This reduces the amount of fuel circulating through the fuel rail and diverts the excess to return through the fuel pressure regulator.
The fuel injectors are provided with regulated fuel for injection but the returned fuel by-passes the engine compartment fuel rail thus lowering the temperature and amount of vaporization that takes place in the fuel tank.
The solenoid is also activated momentarily if an engine misfire is detected. This function provides full fuel flow through the fuel rail to determine if the misfire was caused by a lean fuel condition. The solenoid is monitored by the ECM for faults.
Fuel Pressure Regulator: The Fuel Pressure Regulator maintains a constant "pressure differential" for the fuel injectors.
The fuel pressure is set to 3.5 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 rail distributes an even supply of fuel to all of the injectors, and also serves as a volume reservoir. The fuel rail is secured by bolts to the intake manifold.
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 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.
- Fuel Strainer
- Electrical Connector
- Solenoid Winding
- Closing Spring
- Solenoid Armature
- Needle Valve
- Pintle
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
- Long Crank Time (Leaking)
- Engine Hydrolock (Leaking)
- Oxygen Sensor/Mixture/Injector Related Fault Codes
- Misfire/Rough Idle (Leaking or Blocked)
- Excessive Tailpipe Smoke (Leaking)
Crankshaft Position/RPM Sensor (Hall Effect): This sensor provides the crankshaft position and engine speed (RPM) signal to the ECM for Fuel Pump and Injector operation.
A Hall sensor is mounted on the left side at the rear of the engine block. The impulse wheel is mounted on the crankshaft inside the crankcase, at the rear main bearing support. The impulse wheel contains 58 teeth with a gap of two missing teeth.
The Hall sensor is supplied with voltage from the ECM. A digital square wave signal is produced by the sensor as the teeth of the impulse wheel pass by. The "gap" allows the ECM to establish crankshaft position.
The crankshaft position sensor is monitored as part of OBD II requirements for Misfire Detection. If this input is faulty, the ECM will operate the engine (limited driveability) from the Camshaft Sensor input. A fault with this input will produce the following complaints:
- Hard Starting/Long Crank Time
- Driveability/Misfire/Engine Stalling
- "CHECK ENGINE" Light
Cylinder Identification Signal: An angle pulse generator is used for the camshaft position sensing. The MS41.X ECM uses the signal from the camshaft sensor to set up the fully sequential fuel injection.
This sensor consists of two windings (primary and secondary) that are connected together at one end, and a magnetic core.
The primary winding is supplied with a 120 kHz AC signal. The magnetic coupling causes an induced voltage into the secondary winding (at the same frequency). However the induced voltage has a slight phase shift due to the induction time delay.
The trigger wheel of the camshaft influences the magnet field of the sensor and causes the phase shift to increase as the disc of the wheel moves closer to the sensor. The ECM monitors this change in phase shift as "TDC" (compression input) from the camshaft. When the disc passes by the sensor the phase shift moves closer again.
If this input is defective, the system will still operate based on the Crankshaft Position/RPM Sensor. A fault will be set and the ECM will activate the injectors in parallel. The camshaft position sensor is monitored as part of the requirements for OBD II.
Engine Coolant Temperature: The Engine Coolant Temperature is provided to the ECM from an NTC type sensor located in the coolant jacket of the cylinder head. The sensor contains two NTC elements, the other sensor is used for the instrument cluster temperature gauge.
The ECM determines the correct air/fuel mixture required for the engine temperature by monitoring an applied voltage to the sensor (5v). This voltage will vary (0-5v) as coolant temperature changes the resistance value.
If the Coolant Temperature Sensor input is faulty, a fault code will be set 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. The ECM will maintain fuel injection operation based on the Air Flow Volume Sensor and the Crankshaft Position/RPM Sensor.
Hot-Film Air Mass Meter (HFM): The air volume input signal 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 ECM will operate the engine using the Throttle Position and Engine RPM inputs.
Air Temperature: This signal allows the ECM to make a calculation of air density. 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 ECM will operate the engine using the Engine Coolant Sensor input.