Fuel Injection: Notes
The N74 engine is equipped with high precision injection. This second generation direct fuel injection operates in homogeneous operation at all times and has the same structure as on the N63 engine.
N74 Fuel Injection System
| Index | Explanation |
|---|---|
| 1 | Quantity control valve |
| 2 | High pressure pump |
| 3 | High pressure line (pump - rail) |
| 4 | Rail pressure sensor |
| 5 | Rail |
| 6 | High pressure line (rail - injector) |
| 7 | Fuel feed from the electric fuel pump |
| 8 | Fuel pressure sensor |
| 9 | Feed line |
| 10 | Piezo injector |
The fuel is delivered to the high pressure pump from the fuel tank by the electric fuel pump via the feed line at a delivery pressure of 5 bar. The delivery pressure is monitored by the fuel pressure sensor. The fuel is supplied by the electric fuel pump depending on engine requirements. If this sensor fails, the operation of the electric fuel pump continues with a 100% delivery rate at terminal 15 ON. The fuel is compressed in the permanently driven single-piston high pressure pump and fed via the high pressure line into the fuel rail. The pressurized fuel in the rail is distributed via the high pressure lines to the piezo injectors.
The required fuel pressure is determined by the DME depending on engine speed and load. The pressure reading is picked up by the rail pressure sensor and sent to the DME. Control takes place on the basis of a nominal/actual comparison of the rail pressure by the quantity control valve. With 200 bar of fuel pressure only required at high load and lower engine speed. The purpose of the system is to achieve the smoothest operation with the lowest possible fuel consumption.