Fuel supply, function - GF07.10-P-1003MM
ENGINE 276.8 in MODEL 207, 212 as of model year 2014
ENGINE 276.8 in MODEL 218 as of model year 2015
ENGINE 276.9 in MODEL 204, 207, 212 (except 212.095), 218
Function requirements for fuel supply, general points
- Circuit 15 (ignition ON)
- Circuit 87M (engine timing ON)
Fuel supply, general points
The fuel supply supplies filtered fuel out of the fuel tank in adequate amounts under all operating conditions at an adequate pressure to the fuel injectors (Y76).
Function sequence for fuel supply
The function sequence for fuel supply is described in the following steps:
- Function sequence for fuel low-pressure circuit
- Function sequence for fuel system high-pressure circuit
- Function sequence for safety fuel shutoff
- Function sequence for fuel quality monitoring (for code 494 (USA version) and for code 929 (Engine for ethanol fuel)
Function sequence for fuel low-pressure circuit
Switching on of the fuel pump (M3) takes place when the signal "fuel pump ON" is received by the fuel system control unit (N118). This signal is sent redundantly from the ME-SFI [ME] control unit (N3/10) as a CAN signal via the drive train CAN (CAN C) and as a ground signal. The fuel system control unit also receives the CAN signal "specified pressure of the fuel" from the ME-SFI [ME] control unit.
The fuel system control unit detects the current fuel pressure based on a voltage signal from the fuel pressure sensor (B4/7) (model 204, model 207, model 212), fuel pressure sensor (B4/7) (model 218) and transmits this information via the drive train CAN to the ME-SFI [ME] control unit.
The fuel system control unit evaluates the current fuel pressure, compares it with the specified fuel pressure and actuates the fuel pump with a pulse width modulated signal (PWM signal) as required such that the specified pressure is equivalent to the specified pressure. The fuel pump pressure is controlled dependent on the fuel temperature and the engine RPM between about 4.5 to a maximum of 6.7 bar.
For actuation the fuel pump suctions the fuel from the fuel feed module and pumps it through the fuel filter to the fuel system high pressure pump (single line system without return line).
The overflow valve in the fuel filter opens at a fuel pressure from about 7 to 9 bar. Fuel is removed upstream of the filter over a T-piece which drives the suction jet pump with 20 to 40 l/h. This suction jet pump delivers the fuel out of the left fuel tank chamber into the fuel feed module (in the right fuel tank chamber) and thus prevents single-sided emptying of the fuel tank.
There is a check valve in the feed line to the fuel filter which prevents dropping of the fuel pressure (down to below 4.5 bar) for a switched off fuel pump.
Fuel low-pressure circuit
Function sequence for fuel system high-pressure circuit
In the fuel high-pressure circuit, the fuel high pressure of about 200 bar required for spray guided direct injection is generated, regulated and stored in the rails.
The ME-SFI [ME] control unit reads in the following sensor for regulation of the fuel high pressure:
- Fuel pressure and temperature sensor (B4/25)
The fuel from the fuel tank flows from the low-pressure fuel distributor to the fuel system high pressure pump. This delivers the fuel (according to the operating condition) at a pressure of up to 200 bar and directs it to the fuel injectors via the high-pressure lines and the rails. The three fuel injectors per cylinder head are supplied directly from the associated rail with fuel.
Located on the fuel system high pressure pump is a quantity control valve (Y94) that regulates the fuel quantity fed to the pump element to match the specified fuel pressure.
The fuel pressure and temperature sensor detects the current fuel high pressure as well as the temperature of the fuel in left the rail. The operating pressure is up to about 200 bar. It is only at vehicle standstill and for a selector lever position "N" or "P" that the pressure drops to 150 bar in order to reduce the noise emissions from the fuel system high pressure pump.
In the case of shutting off a vehicle with a hot engine, the fuel pressure can increase up to 250 bar (+17 bar) in the fuel high-pressure circuit. Upon reaching this threshold a pressure limiting valve opens in the fuel system high pressure pump and the pressure is reduced. Upon starting the engine the pressure falls rapidly to the normal operating pressure of 200 bar.
In order to achieve rail pressure regulation, the quantity control valve is actuated by means of a PWM signal by the ME-SFI [ME] control unit until the fuel specified pressure is set up in the rail.
There are leakage lines on both rails which, in the case of a leak on the sealing rings for the fuel injectors to the rail, lead the fuel into the cylinder head. This prevents fuel escaping and thus any possible ignition on hot engine parts.
During regulation of the fuel high-pressure circuit one differentiates between the following operating conditions:
- Start
- Normal mode
- Low-pressure limp-home mode (fuel high pressure is not reached)
- Stop
Start
- The quantity control valve is energized and closed, so there is full delivery from the fuel system high pressure pump and rapid pressure buildup.
- Fuel pump pressure is approx. 4.5 up to 6.7 bar.
Normal mode
- The quantity control valve regulates over the duty cycle of the fuel high pressure.
- Fuel pump pressure is dependent on the fuel temperature between about 3.0 to 5.5 bar.
- The fuel predelivery pressure is dependent on the engine speed and fuel temperature and varies between 4.5 and 6.7 bar (absolute).
Low-pressure limp-home mode (fuel high pressure is not reached)
- The quantity control valve is deenergized and therefore opened.
- Fuel pump pressure about 4.5 to 6.7 bar, fuel flows over the open quantity control valve into the rails.
- Actuation of fuel injectors extended.
- Blocked stratified operation (for code (920) Gasoline direct injection with stratified charge).
- Performance reduction, max. speed about 70 km/h.
Stop
- Quantity control valve is deenergized and opened.
- Fuel pump not actuated
Assembly operations
The high pressure fuel lines made out of stainless steel can be reused after checking. An appropriate test specification can be found in the repair instructions.
Fuel high-pressure circuit
Function sequence for safety fuel shutoff
The safety fuel shutoff system is designed to ensure traffic and passenger safety.
The ME-SFI [ME] control unit controls the safety fuel shutoff on the basis of the following sensors and signals:
- Crankshaft Hall sensor (B70), engine RPM
- Throttle valve positioner (M16/6), throttle valve position
- Supplemental restraint system control unit (N2/10) (model 204), supplemental restraint system control unit (N2/10) (model 207, 212, 218)
- Supplemental restraint system control unit or supplemental restraint system control unit, indirect crash signal via the chassis CAN (CAN E) (up to model year 2014)
- Supplemental restraint system control unit or supplemental restraint system control unit, indirect crash signal via the chassis CAN 1 (CAN E1) (as of model year 2014)
The safety fuel shutoff is activated by the ME-SFI [ME] control unit for the following conditions:
- Mechanical fault in the throttle valve actuator
- Absence of the engine speed signal
- Crash signal
Mechanical fault in the throttle valve actuator
When evaluating the throttle valve position, if the ME-SFI [ME] control unit detects a mechanical fault in the throttle valve actuator, engine speed is limited to about 1400 RPM at idle and about 1800 RPM in driving mode by shutting off the fuel injectors.
Absence of the engine speed signal
If the engine speed signal generated by the crankshaft Hall sensor is missing, the fuel pump is shut off via the fuel system control unit.
Crash signal
If the ME-SFI [ME] control unit receives a crash signal indirectly via the chassis CAN or directly from the supplemental restraint system control unit or supplemental restraint system control unit, it switches off the fuel pump via the fuel system control unit (directly and via the drive train CAN) and the quantity control valves, in order to depressurize the fuel system.
Function sequence for fuel quality monitoring (for code 494 (USA version) and for code 929 (Engine for ethanol fuel)
With the ever higher increase in the admixture of ethanol into the fuel it has become necessary to monitor the ethanol content or the fuel ethanol mixture. Variations in the stoichiometric fuel air/fuel ratio can occur due to the variable ethanol contents. This can lead to a loss of engine power.
Monitoring takes place by means of the fuel quality sensor (B4/31) which detects the relative conductivity of the gasoline ethanol mixture. The value of the relative conductivity is dependent on the gasoline ethanol mixture and the fuel temperature. This value is measured by the fuel quality sensor and is transmitted with an appropriate voltage signal to the FSCU. There it is converted and sent as information to the ME-SFI [ME] control unit in order to undertake the appropriate adaptation of the engine timing.
The power supply of the fuel quality sensor takes place from the FSCU.
| Electrical function schematic for fuel supply | MODEL 204 | PE07.10-P-2703-97FAK | |
| MODEL 207 | PE07.10-P-2703-97EAH | ||
| MODEL 212 | PE07.10-P-2703-97DAI | ||
| MODEL 218 | PE07.10-P-2703-97XAB | ||
| Electrical function schematic for safety fuel shutoff | MODEL 204 | PE07.10-P-2733-97FAK | |
| Model 207 up to model year 2014 | PE07.10-P-2733-97EAH | ||
| Model 207 as of model year 2014 | PE07.10-P-2733-97EAK | ||
| MODEL 212 up to model year 2014 | PE07.10-P-2733-97DAI | ||
| MODEL 212 as of model year 2014 | PE07.10-P-2733-97DAQ | ||
| MODEL 218 up to model year 2014 | PE07.10-P-2733-97XAB | ||
| MODEL 218 as of model year 2014 | PE07.10-P-2733-97XAI | ||
| Overview of system components for gasoline injection and ignition system with direct injection | ENGINE 276.9 in MODEL 204, 207, 212 (except 212.095), 218 | GF07.70-P-9998MM | |
| ENGINE 276.8 in MODEL 207, 212 as of model year 2014 ENGINE 276.8 in MODEL 218 as of model year 2015 |
GF07.70-P-9998MMP |