Fuel Delivery and Air Induction: Description and Operation
Fuel systemThe N14 4-cylinder petrol engine works with direct fuel injection. Direct fuel injection increases performance. The fuel delivery pressure is a maximum of 120 bar (idle speed: 50 bar, full load: 120 bar).
The use of direct fuel injection creates a homogeneous mixture formation in the entire combustion chamber. Homogeneous mixture formation means that the fuel-air ratio is regulated stoichiometrically in the same way as for intake pipe fuel injection (Lambda = 1). "Stoichiometrically" refers to a fuel-air ratio of 14.7 kilograms of air to 1 kilogram of fuel. The homogeneous mixture formation means that conventional exhaust gas treatment can be deployed.
Brief description of components
The following components are described for the fuel injection:
High-pressure fuel valve
The high-pressure fuel valve is located on the side of the cylinder. In the case of fully sequential fuel injection, each high-pressure fuel valve is activated by the DME control module via a separate output stage. Here, the fuel injection time of each cylinder is adapted to the operating status (speed, load and engine temperature).
Index Explanation
1 Valve seat
2 Needle
3 Coil
4 Connecting cable
5 Filter
6 Setting disc
High-pressure pump with volume control valve
2 pistons in the high-pressure pump generate the necessary pressure in the fuel system. The inlet camshaft drives the high-pressure pump mechanically. The maximum fuel delivery pressure is 120 bar. There is a volume control valve on the high-pressure pump. The digital engine electronics control module activates the volume control valve.
Index Explanation
1 High-pressure pump
2 Volume control valve
3 Plug-in connection
Rail pressure sensor
The rail-pressure sensor fitted on the stainless steel rail. In the rail, the compressed fuel is stored temporarily and distributed to the high-pressure fuel valves. A silicon element on a metal membrane measures the fuel delivery pressure in the rail. The measuring range of the rail-pressure sensor is from 0 to 160 bar. The rail-pressure sensor delivers a proportional voltage over the entire measuring range.
Index Explanation
1 Rail
2 Rail pressure sensor
If the rail-pressure sensor fails, the volume control valve is activated in emergency operation by the DME.
Electrical Fuel Pump
The electric fuel pump is an in-tank pump. The DME activates the fuel pump via the fuel-pump relay. The fuel-pump relay is in the junction box electronics.
Index Explanation
1 Digital Engine Electronics (DME)
2 Fuel pump relay
3 Junction box electronics (JBE)
4 Electrical Fuel Pump
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.
Index Explanation
1 2-pin plug-in connection
2 Tank ventilation valve
The tank vent valve is closed when in a flow-free state. This means that with the engine at a standstill no fuel vapors from the activated carbon filter enter the intake pipe.
System functions
The following system functions are described for the fuel system:
High-pressure control
The volume control valve adjusts the flow of fuel from the low-pressure side into the high-pressure side of the high-pressure pump. This achieves the desired rail pressure. The volume control valve is forced open hydraulically as of a certain pressure in the high-pressure side of the high-pressure pump. The volume control valve is a component of the high-pressure pump.
The signal from the rail-pressure sensor is an important input signal of the DME for activation of the volume control valve (component of the high-pressure pump). If the rail-pressure sensor fails, the volume control valve is activated in emergency operation by the DME.
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 vapors from the activated carbon filter enter the intake pipe.
Notes for Service department
General information
Note! The volume control valve cannot be replaced individually.
Due to the risk of soiling, only the complete high-pressure pump may be replaced.
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 switchover valve in the diagnosis module is in the position "Regeneration". The fuel vapors 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 code 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 switchover 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 switchover 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 switchover 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.