Fuel System
Fuel System
The 4-cylinder N12 petrol engine works with an individual-cylinder, fully sequential fuel injection. The individual-cylinder, fully sequential fuel injection has the following advantages:
- Optimized fuel preparation for each individual cylinder
- Adaptation of the fuel injection period to suit the engine's operating condition (engine speed, load, temperature)
- With changing loads, cylinder-selective injection correction (during an intake stroke, the fuel injection period can be corrected by a later injection, an extension or shortening)
- Cylinder-selective cutoff (e.g. when an ignition coil is defective) is possible
- Diagnosis of each individual fuel injector is possible.
Brief description of components
The following components are described for the fuel injection:
Fuel injector
The fuel injector is arranged on top of the cylinder. During fully sequential fuel injection, each injector is controlled by the DME control module via its own final stage. Here, the fuel injection time of each cylinder is adapted to the operating status (speed, load and engine temperature).
Fuel pump and fuel-pump relay
The electric fuel pump is an in-tank pump. The fuel pump relay activates the electric fuel pump. The DME control module monitors the activation of the fuel pump relay. The fuel pump relay is controlled via a safety circuit only when the engine is running and shortly after terminal 15 ON for pressure build-up (delivery line for fuel pump). The fuel-pump relay is in the junction box.
The maximum fuel pressure is approximately 5 bar.
With terminal 15 On, a fuel-pump relay switches on the electric fuel pump.
Tank ventilation valve
The tank-ventilation valve regenerates the activated carbon filter by means of purge air. The purge air drawn through the activated carbon filter is enriched with hydrocarbon and then fed to the combustion engine.
The tank vent valve is closed when in a flow-free state. This means that with the engine at a standstill no fuel vapours from the activated carbon filter enter the intake pipe.
System functions
The following system functions are described for the fuel system:
Bleeding the tank
The tank-ventilation valve controls the regeneration of the activated carbon filter by means of purge air. The purge air drawn through the activated carbon filter is enriched with hydrocarbon (HC) depending on the load of the activated carbon. The purge air is then fed to the engine for combustion.
The creation of hydrocarbons in the fuel tank depends on:
- Fuel temperature and ambient temperature
- Air pressure
- Fill level in the fuel tank
The tank vent valve is closed when in a flow-free state. This means that with the engine at a standstill no fuel vapours from the activated carbon filter enter the intake pipe.
Notes for Service department
National version US
Diagnosis module for tank leakage (DMTL)
The leak test of the fuel system is run regularly after stopping the engine. The following processes run in the after-run time of the DME:
- Initial situation
During normal engine operation, the changeover valve in the diagnosis module is in the position "Regeneration". The fuel vapours are stored in the carbon canister and fed to the engine as a function of activation of the tank-venting valve (see also Tank ventilation).
- Check of start conditions
The necessary start conditions are checked after the engine is switched off:
- Engine OFF
- Battery voltage between 11.5 and 14.5 Volts
- No fault memory entries in the DME for the diagnosis module for tank leakage as well as tank-ventilation system
- Tank fill level greater than 10 % and less than 90 %
- Ambient temperature between -7 °C and 35 °C
With a positive result, the tank-leak diagnosis is started with a comparison measurement.
- Comparison measurement
The tank-venting valve is always closed after the engine is switched off. The changeover valve of the diagnosis module remains in the position "Regeneration". The electrical leakage diagnosis pump pumps fresh air from the environment via a defined leak of 0.5 mm diameter. The necessary current consumption is stored as a value. This is followed by the tank-leak diagnosis itself.
- Tank-leak diagnosis
The tank-venting valve remains closed. The changeover valve of the diagnosis module switches to the position "Diagnosis". The leak diagnosis pump pumps fresh air from the environment into the fuel tank, slowly raising the internal pressure. At the start of the tank-leak diagnosis, the internal pressure corresponds to the ambient pressure. The current consumption is thus low. With increasing internal pressure in the tank, the current consumption rises. The current consumption of the leak diagnosis pump is evaluated by the DME.
- Evaluation of the pump current
The DME evaluates the rise in the current consumption within a certain time. If the current consumption exceeds the stored value within this time, the fuel system is regarded as OK. The tank-leak diagnosis is terminated. If the current consumption does not reach the stored value, the fuel system is regarded as not OK.
The tank-leak diagnosis enables a distinction between:
- Major leak, e.g. fuel filler cap missing
- Minor leak
- Minimal leak
The relevant fault is entered in the DME fault memory. Tank-leak diagnosis is then terminated.
- End of the tank-leak diagnosis
The changeover valve is switched back to the position "Regeneration". The after-run time of the DME is available for other functions.
The tank-leak diagnosis can also be started using the BMW diagnosis system. In this case, the processes take place as described above.
No liability can be accepted for printing or other faults. Subject to changes of a technical nature