Fuel Delivery and Air Induction: Description and Operation
GF07.61-P-3004M ME Fuel Supply, Function
Component Identification:
The fuel supply system must make available to the fuel injectors an adequate quantity of filtered fuel from the fuel tank and at an adequate pressure in all operating conditions.
The fuel pump (M3) suctions the fuel out of the fuel tank (75) and delivers it through the fuel filter (55/1) with integrated overflow valve to the injection valves (Y62) at the fuel distribution tube (17) (single- line system). The fuel injectors operated by the ME-SFI control unit, spray the finely atomized fuel into the inlet port.
The return flow from the overflow valve flows back into the fuel tank and supplies the suction jet pump for filling the swirl pot in the fuel tank. The overflow valve opens by means of a fuel pressure at approx. 3.5 bar.
The fuel pressure sensor (B4/7) downstream of the fuel filter detects the fuel pressure and gives a signal to the fuel pump control unit (N118).
The voltage supply for the fuel pump control unit (N118) is performed via the fuel pump relay.
Via a PWM signal, the rotational speed of the fuel pump is then regulated in such a manner that the system pressure of approx. 3.8 bar (about 5 bar in United States of America from 6/05) is kept constant. If the fuel pressure e. g. drops below approx. 3.7 bar, the delivery quantity (rotational speed) of the fuel pump is increased, until the system pressure is reached again.
At maximum power consumption of fuel pump of about 16 A about 9 bar of fuel pressure is achieved (clutch on fuel pressure sensor removed, not for model 240 with ME2.7.2 from 1.9.06).
Model 240 with ME2.7.2 from 1.9.06
The signal from the fuel pressure sensor with the current fuel pressure is read in at the fuel pump control unit and sent to the ME- SFI control unit via the CAN. In the ME-SFI control unit, the fuel pressure is checked for plausibility and sent back to the fuel pump control unit as a fuel pump target preset. The delivery amount (rotational speed) of the fuel pump is regulated in such a way via PWM signals until the required system pressure (about 3.8 bar, for a hot start up to about 5.5 bar) is reached.
Model 230 as of 1.12.06
The fuel pressure sensor now measures the absolute value with an altered connection assignment and appropriately altered pin assignment at the fuel pump control unit.
If the new fuel pressure sensor is installed in older vehicles then the individual plug in the plug connector should be adapted appropriately:
If the fuel pressure is too low, combustion misfires can occur and can be retracted in the diagnostic trouble code memory. The cause can be, for example, a contaminated fuel filter.
In these cases, check the maximum fuel pump delivery rate at the feed to the fuel distributor rail.
To do this detach the electrical connector on the fuel pressure sensor (B4/7) so that the fuel pump is fully actuated by the fuel pump control unit (N118) (not for model 240 with ME2.7.2 from 1.9.06).
Model 240 with ME2.7.2 from 1.9.06: actuate fuel pump using STAR DIAGNOSIS. Using STAR DIAGNOSIS, the fuel pressure and flow through the fuel pump can be read out.
Fuel vapors out of the fuel tank are temporarily stored in the activated charcoal canister (77) and burnt in the engine via the purge control valve (Y58/1) at suction operation.
Observe risk of confusion between the outer fuel filters with similar structures.
- Fuel filter with integrated diaphragm pressure regulator (Engine 111, 112, 113, 137)
- Fuel filter with integrated overflow valve (Engine 275.950/951, 285)
- Fuel filter with integrated overflow valve, without throttle (engine 275 AMG).
