Fuel Tank: Description and Operation
Fuel Tank
Fuel tank
The fuel tank of the N55 engine is equipped with different components.
Brief component description
The following components are described for the fuel tank:
- Tank vent shutoff valve
- Tank vent valve
- Fuel level sensor 1 (left) and fuel level sensor 2 (right).
Tank vent shutoff valve
The tank vent shutoff valve is necessary for a diagnosis of the tank ventilation system.
The N55 engine has two purge air lines from the tank vent valve to the air intake duct:
1. from the fuel tank ventilation valve via the suction jet pump valve before the twin-scroll exhaust turbocharger
2. from the tank vent valve to the throttle body.
Both lines must therefore be checked for throughflow in the event of malfunctions.
When the first purge air line is being checked, the second is closed using the shutoff valve.
The amount of fuel vapor drawn in by the combustion engine from the activated carbon canister must be adapted to each operating condition of the engine. The fuel tank ventilation shutoff valve is activated by the Digital Engine Electronics (DME).
The following graphic shows the tank ventilation system on the F10.
Fuel level sensor 1 (left) and fuel level sensor 2 (right)
2 fuel level sensors are installed in the fuel tank, one in each half of the tank.
The fuel tank level is determined by the fuel level sensors and displayed on the instrument panel (KOMBI). 1 fuel level sensor consists of the following components:
- Potentiometer with sliding contacts and potentiometer tracks
- Lever arm
- Float.
Only fuel level sensor 2 (right) can be replaced. Fuel level sensor 2 (right) is installed in the right half of the fuel tank.
The fuel gauge in the instrument panel (KOMBI) displays the fuel tank level as of terminal 15 ON. The Junction Box Electronics (JBE) provide the two fuel level sensors with electrical power. The junction box electronics (JBE) determine a resistance value via the voltage drop at the potentiometers (depending on the filling level) and transmit this to the instrument panel (KOMBI). The fuel tank level is determined in litres in the instrument panel (KOMBI) via a characteristic curve.
The joint of the fuel level sensors contains a potentiometer with sliding contacts and potentiometer tracks. The position of the float and therefore the lever arm changes depending on the fuel tank level. This means that a certain resistance value can be assigned to each angle.
The following graphic shows the fuel level sensors on the F10.
The measuring range of the fuel level sensor from approx. 0 to 200 millimetres corresponds to, for example in a possible encoding variant, 75 litres (total fuel tank capacity, for example 82 litres).
System overview
General notes
NOTICE: Allow the engine to cool down.
Never start repair work on the fuel system without allowing the engine to cool down first. The coolant temperature must not exceed 40 °C. Compliance with this instruction is absolutely vital, as otherwise residual pressure within the high-pressure fuel system could result in uncontrolled fuel spray.
NOTICE: Protect ignition coils against contamination.
When carrying out repair work on the N55 always ensure that the ignition coils are not contaminated by fuel. Contact with fuel substantially reduces the ability of silicone to provide effective sealing. The result would be arcing between the spark plugs and the cylinder head, leading to ignition miss. Prior to working on the fuel system always remove the spark plugs and seal off the spark plug wells with shop towels to protect them from fuel.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.