Page 60 - E BOOK ENGINE MECHANICAL M2

3. FUEL SYSTEM

<Pump Learning>
In order to properly match the tolerances of the mechanical pump with the operation of the electronic
control unit, the Engine-ECU has to learn the actual pump characteristics. In this learning, the En-
gine-ECU operates the suction control valve as it monitors the voltage output of the common rail
pressure sensor. The Engine-ECU compares the results against the map values stored in its memory
of the relationship between the fuel pressure and the required amperage to operate the suction con-
trol valve, and learns or remembers this value. If the supply pump is replaced, the Engine-ECU has
to learn the value for the new pump.
This learning process is performed with the MUT-III after the engine has been warmed up, and in a
completely no-load state.
The learning procedure can be found in the following section of this textbook.
→Part 2: Common Rail Fuel Injection System →Chapter 6. On-vehicle Inspection & Service
→6. Supply Pump Correction Learning.

(3) Common Rail
The common rail stores the fuel under pressure (0 to
180MPa or 135MPa) that has been delivered from the
supply pump, and distributes the fuel to the injectors of
the cylinders through the high pressure pipes. The rail
pressure sensor and the pressure limiter are attached to
the common rail.
Rail pressure sensor

Fuel pressure limiter valve
Fig. 3-9

<Fuel Pressure Limiter Valve>
The fuel pressure limiter valve is a spring-loaded me-
chanical valve designed to open and release fuel when
the pressure in the common rail reaches approximately
221MPa.
When the pressure drops to 50MPa, the spring load
forces the pressure limiter to return its normal closed
state to maintain the proper pressure inside the com-
mon rail.
Fuel pressure

Fig. 3-10

Fig. 3-11

Pub. No. PTAE1228 3 - 6