C
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HP pipe connection – fuel rail to injector (4 off)
1
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Fuel rail
2
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PCV
3
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Fuel rail pressure sensor
The fuel rail is manufactured from forged steel and secured to the cylinder head with 2 fixings. The fuel rail stores
pressurized fuel from the HP pump, and prevents pressure fluctuations in the HP system. A fuel rail pressure sensor and a
PWM PCV are installed into the bore at each end of the fuel rail. The pressure sensor is installed at the accessory drive
end of the fuel rail; the PCV installed at the transmission end of the fuel rail.
High-pressure fuel pipes connect the fuel rail to the HP pump and fuel injectors. A leak-off pipe connects the fuel rail to
the fuel filter return circuit.
The common fuel rail, fuel pressure sensor and PCV form an integral assembly, and must not be separated. If a fault
occurs that requires component renewal, then the complete fuel rail assembly must be renewed.
Fuel Rail Pressure Sensor
The fuel rail pressure sensor is mounted in the end of the fuel rail (accessory drive end) and connected to the ECM via the
engine harness. The pressure sensor is provided with a 5V power supply, ground and signal connections. The fuel rail
pressure sensor is a piezo-resistive type sensor containing an actuating diaphragm. Deflection of the diaphragm provides a
proportional signal (output) voltage to the ECM, dependant on the fuel pressure within the fuel rail.
Pressure Sensor Parameters
Pressure Sensor Output Voltage
Fuel Rail Pressure
0.5V
230 bar (3,336 psi)
4.5V
1,600 bar (23,206 psi)
The ECM compares the sensor signal voltage to stored memory values, in order to calculate the actual fuel pressure
present in the fuel rail. The ECM then uses the fuel rail pressure information to control the operating position of the VCV
and PCV.
For additional information, refer to: Electronic Engine Controls - 2.2L Diesel (303-14 Electronic Engine Controls - 2.2L
Diesel, Description and Operation).
Pressure Control Valve (PCV)
The PCV is mounted in the end of the fuel rail (transmission end) and connected to the ECM via the engine harness. The
PCV is a solenoid-operated valve controlled by a 12V PWM signal. The ECM operates the PCV to adjust the fuel pressure
within the fuel rail. Relieved fuel is directed through the fuel rail leak-off pipe to the fuel filter return circuit. The leak-off
fuel also provides cooling and lubrication for the PCV.
For additional information, refer to: Electronic Engine Controls - 2.2L Diesel (303-14 Electronic Engine Controls - 2.2L
Diesel, Description and Operation).
The PCV is normally open when the solenoid is not energized by the ECM. The resistance value of the PCV solenoid coil is
3.6 ohms at 20°C (68°F).
The PCV is also used by the ECM to provide direct control of the fuel system, in the following situations:
During sudden transient phases in engine speed (suddenly lifting off the accelerator pedal, for example) where VCV
action is not sufficient to affect the supply of fuel to the fuel rail.
To control fuel pressure in the event that the VCV fails.
During the fuel heating period, when supply fuel temperature is less than 40°C (104°F). The VCV is fully opened by
the ECM and the HP pump compresses a maximum quantity of fuel to raise the fuel temperature. The PCV is then
modulated by the ECM to provide leak-off fuel from the fuel rail to the fuel filter return circuit. The fuel is then
recirculated through the fuel filter and back to the HP pump.
When the fuel supply temperature is greater than 70°C (158°F). The PCV is modulated by the ECM to release fuel
rail pressure, subsequently decreasing the fuel temperature to protect the fuel system components. Leak-off fuel
from the fuel rail is directed to the fuel filter return circuit and back to the fuel tank.
During engine shutdown to progressively collapse fuel rail pressure.
FUEL INJECTORS