Fuel Supply, Function - GF07.10-P-1003MNA
Engine 177.9 in model 205, 253
Engine 177.9 in model 213
up to model year 2021
Function requirements, general
- Circuit 87M (Engine management) ON
The electronic ignition lock control unit (N73) transmits the status of circuit 15 via the chassis FlexRay (Flex E), the powertrain control unit (N127) and the drive train CAN (CAN C1) to the ME-SFI [ME] control unit (N3/10). The ME-SFI [ME] control unit then actuates the circuit 87M relay (K40/8kN). The circuit 87M relay switches the battery voltage (circuit 30) to circuit 87M. When circuit 87M is switched through to the ME-SFI [ME] control unit, it starts the engine management.
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 system high pressure pumps.
Fuel low-pressure circuit
The fuel low-pressure circuit provides the fuel supply to the fuel system high pressure pumps.
The ME-SFI [ME] control unit transmits the switch on fuel pump (M3) request via a direct line and redundantly via the drive train CAN to the fuel system control unit (N118). The ME-SFI [ME] control unit also transmits the specified fuel pressure via the drive train CAN to the fuel system control unit. The ME-SFI [ME] control unit calculates the specified fuel pressure (fuel requirement) from the current fuel pressure and the load requirement of the engine. Depending on the fuel requirement, with fuel pressure of approx. 4 to 6.7 bar, a fuel delivery volume of 0 to 130 l/h is regulated in this way.
The fuel system control unit accordingly actuates the fuel pump, evaluates the fuel pressure and transmits this via the drive train CAN to the ME-SFI [ME] control unit. The fuel pressure is recorded by the fuel pressure sensor (B4/7). The fuel system control unit reads in the signals of the fuel pressure sensor directly.
The fuel pump suctions the fuel from the fuel feed module and pumps it through the fuel filter to the high pressure fuel pumps (single line system without return line). The overflow valve in the fuel filter opens at a fuel pressure of approx. 7 to 9 bar. There is a check valve in the feed line to the fuel filter which prevents dropping of the fuel pressure (down to below approx. 4.5 bar) for a switched-off fuel pump.
Engine 177.9 in model 205, 253
with code 494 (US version)
Engine 177.9 in model 213
up to model year 2021
with code 494 (US version)
The fuel pressure sensor also records the fuel temperature.
Fuel high-pressure circuit
In the fuel high-pressure circuit, the fuel high pressure of about 200 bar that is required for spray-guided direct injection is generated, regulated and stored in the rails.
The left quantity control valve (Y94/1) is located on the left fuel system high pressure pump and the right quantity control valve (Y94/2) on the right. The quantity control valves regulate the amount of fuel that is fed to the pump elements in the high pressure fuel pumps depending on the requirement and the characteristics map.
The ME-SFI [ME] control unit evaluates the signals from the following sensors for this:
- Right fuel pressure and temperature sensor (B42/1)
- Left fuel pressure and temperature sensor (B42/2)
The ME-SFI [ME] control unit actuates the quantity control valves accordingly. The fuel pressure and temperature sensors are located at the rails.
The fuel system high pressure pumps deliver the fuel via the high-pressure lines and the rails to the following components of the fuel injection system, which are then actuated accordingly by the ME-SFI [ME] control unit:
- Cylinder 1 fuel injector (Y76/1)
- Cylinder 2 fuel injector (Y76/2)
- Cylinder 3 fuel injector (Y76/3)
- Cylinder 4 fuel injector (Y76/4)
- Cylinder 5 fuel injector (Y76/5)
- Cylinder 6 fuel injector (Y76/6)
- Cylinder 7 fuel injector (Y76/7)
- Cylinder 8 fuel injector (Y76/8)
In engine idle and selector lever position "N" or "P", the pressure is lowered to approx. 130 bar in order to reduce the noise emissions of the high pressure fuel pumps.
When a hot engine is stopped, the fuel pressure can increase to as much as 250 bar (+17 bar). In this case, quantity control valves are opened at the high pressure fuel pumps and the pressure is reduced. During regulation of the fuel high pressure, a distinction is made between the following operating states:
- Start
- Normal mode
- Low-pressure limp-home mode (fuel high pressure is not reached)
- Stop
Start
The quantity control valves are energized and thus closed. The fuel system high pressure pumps deliver at maximum output. The pressure in the rails is built up quickly. The fuel pump pressure is 4.5 to 6.7 bar at the low-pressure side.
Normal mode
The ME-SFI [ME] control unit actuates the quantity control valves over pulse width modulated signals and thus regulates the necessary fuel quantity. The fuel pump pressure is approx. 4.5 to 6.7 bar at the low-pressure side (depending on the engine RPM and the fuel temperature).
Low-pressure limp-home mode (fuel high pressure is not reached)
The quantity control valves are not energized and thus open. The fuel pump pressure is 4.5 to 6.7 bar. Fuel is flowing into the rails via the open quantity control valves. The fuel injectors are actuated for longer. In low-pressure limp-home mode, the engine is operated at reduced power. The maximum speed is 70 km/h.
Stop
The quantity control valves are not energized and thus open. The fuel pressure in the rails is reduced. The fuel pump is no longer actuated.
Assembly operations
The high pressure fuel lines made out of stainless steel can be reused after checking.
View of the fuel high-pressure circuit
Safety shutoff
In the event of an accident, the ME-SFI [ME] control unit switches the engine off and stops the fuel supply.
The Supplemental Restraint System control unit (N2/10) transmits the crash signal via a direct line (analog) and also via the user interface CAN (CAN HMI), the electronic ignition lock control unit, chassis FlexRay (Flex E), the powertrain control unit and the engine CAN (CAN C) to the ME-SFI [ME] control unit. The ME-SFI [ME] control unit then stops the actuation of the fuel injectors, the quantity control valves and the fuel pump. The engine is switched off. The fuel pressure is reduced in the fuel high-pressure circuit. There is less risk of fire after an accident.
| Electrical function schematic for fuel supply | Engine 177.9 in model 205, 253 | PE07.10-P-2703-97FBD | |
| Engine 177.9 in model 213 up to model year 2021 | PE07.10-P-2703-97DBG | ||
| Electrical function schematic for safety fuel shutoff | Engine 177.9 in model 205, 253 | PE07.10-P-2733-97FBD | |
| Engine 177.9 in model 213 up to model year 2021 | PE07.10-P-2733-97DBG | ||
| Overview of system components for gasoline injection and ignition system with direct injection | Engine 177.9 in model 205, 253 | GF07.70-P-9998MNA | |
| Engine 177.9 in model 213 up to model year 2021 | GF07.70-P-9998MNE |