Isuzu 2008MY N Series Workshop Manual page 392

Fuel Rail (Common Rail)
Legend
1. Pressure limiter valve
2. Fuel rail pressure (FRP) sensor
Along with the employment of a common rail type
electronic control fuel injection system, the fuel rail is
provided to store high pressure fuel between supply
pump and injectors. A pressure sensor and a pressure
limiter are installed on the fuel rail. The pressure sensor
detects the fuel pressure inside the fuel rail and sends
its signal to the ECM. Based on this signal, the ECM
controls the fuel pressure inside the fuel rail via the fuel
rail pressure (FRP) regulator of the supply pump. The
pressure limiter opens the valve mechanically to relieve
the pressure when the fuel pressure inside the fuel rail
is excessive.
Fuel Rail Pressure Sensor
The FRP sensor is installed to the fuel rail and it
detects the fuel pressure in the fuel rail, converts the
pressure into a voltage signal, and sends the signal to
the ECM. The ECM monitors the FRP sensor signal
voltage. Higher fuel rail pressure provides higher signal
voltage while lower pressure provides lower signal
voltage. The ECM calculates actual fuel rail pressure
(fuel pressure) from the voltage signal and uses the
result in fuel injection control and other control tasks.
Pressure Limiter Valve
469%$-50
Legend
The pressure limiter relieves pressure by opening the
valve if abnormally high pressure is generated. The
valve
approximately 220 MPa (32,000 psi), and closes when
pressure falls to approximately 50 MPa (7,250 psi).
Fuel leakage through the pressure limiter re-turns to
the fuel tank.
Fuel Rail Pressure (FRP) Regulator
Engine Control System (4HK1)
1 2 3
6
1. Valve
2. Valve body
3. Valve guide
4. Spring
5. Housing
6. Fuel rail
7. Fuel return pipe
opens when pressure
1
2
1A-389
4 5
7
LNW41ASH001301
in rail reaches
LNW76ESH001901