Fuel Delivery and Air Induction: Description and Operation

GF07.61-P-3004MA ME Fuel Supply, Function

Component Identification:

To meet the requirements of an adequate fuel pressure with an appropriate delivery quantity, even at high loads and speeds, a fuel system consisting of a fuel pump with an increased capacity (up to approx. 330 l/h) and on models 215, 220 and model 230 up to about 28.2.06 an intank fuel pump is used.

The fuel pump (M3) suctions the fuel from the swirl pot (55/4) in the fuel tank (75) and delivers it to the fuel filter with an integrated overflow valve (55/1), where impurities are removed. The fuel pressure sensor (B4/7) records the fuel pressure as per the fuel filter.

Model 215, 220 and model 230
Model 240 with ME2.7.1 up to 31.8.06
The signal fuel pressure passes to the fuel pump control unit (N118). With a PWM signal, the rotational speed of the fuel pump is regulated in such a manner that the system pressure of approx. 3.8 bar is kept constant. If the fuel pressure drops
e.g. below approx. 3.7 bar, the delivery quantity (rotational speed) of the fuel pump is increased until the system pressure is reached again. The overflow valve in the fuel filter opens at approx. 3.5 bar.
Therefore, some of the fuel flows back into the fuel tank through the fuel pressure valve (55/3). This return flow operates the suction jet pump (95) in the swirl pot. The suction jet pump fills the swirl pot with fuel.
In order to limit the fuel feed to the suction jet pump (50 l/h), a throttle (55/3a) is provided in the line to the suction jet pump.
The fuel pressure valve (55/3) opens at approx. 4.1 bar. It is shut in normal mode and is used to quickly reduce pressure peaks.

Model 240 with ME2.7.2 from 1.9.06
The signal from fuel pressure sensor with the current fuel pressure is read in at the ME-SFI [ME] control unit. The fuel pressure is checked for plausibility in the ME-SFI [ME] control unit and reported back as a fuel pressure specification via a PWM signal to the fuel pump control unit. The delivery rate (rotational speed) of the fuel pump is regulated by means of a PWM signal until the delivered system pressure of about 4.0 to 5.5 bar is reached.
A pressure relief valve is located in the fuel tank. It opens at about 5.2 bar and ensures at a high load that the swirl pot with the suction jet pump (nozzle 0.6 mm) is adequately filled.

Model 215, 220 and model 230 up to about 28.2.06
In case of a higher engine load and speed, in addition to the suction jet pump, the intank fuel pump (M3/1) also fills the swirl pot with a maximum delivery rate of 220 l/h. The voltage supply to the intank fuel pump takes place via the intank fuel pump relay (K40/8kX, K27/5). This is actuated via output from the fuel pump control unit (N118), if the duty cycle for the fuel pump (M3) is longer than 5 s, greater than 72 %.

In practical operation, the intank fuel pump is connected only if the speed exceeds 250 km/h and when the tank is almost empty.

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 delivery rate of the fuel pump (approx. 330 liters per hour) at feed to fuel distribution tube. To do this at ME2.7.1 up to 31.8.06 unplug the electric connection at the fuel pressure sensor (B4/7) so that the fuel pump is fully actuated from the fuel pump control unit (N118). At least one liter of fuel flows in 15 s.

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.

Voltage supply to the fuel pump control unit (N118) takes place via the fuel pump relay that is actuated by the ME-SFI control unit (N3/10).

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, 285.95)
- Fuel filter with integrated overflow valve, without throttle (engine 275.98, 285.98).