Isuzu 2008MY N Series Workshop Manual page 391

1A-388 Engine Control System (4HK1)
3) Injection end
The TWV lowers to close the outlet orifice, when the
ECM shuts off a current supply to the solenoid. As a
result, the fuel cannot leak from the control chamber,
and thus the fuel pressure in the control chamber rises
abruptly and then the nozzle is pushed down by the
command piston to close the nozzle injection holes,
resulting in the end of fuel injection.
Fuel Supply Pump
Injector
Fuel tank
The fuel supply pump is the heart of the common rail
type electronic fuel injection system. The fuel supply
pump is installed at the same location as the
conventional injection type pump, which spins at a 1 to
1 ratio of fuel supply pump to crankshaft speed. A fuel
rail pressure (FRP) regulator and fuel temperature
sensor are part of the fuel supply pump assembly.
Fuel is drawn from the fuel tank via the fuel supply
pump by the use of an internal feed pump (trochoid
type). This feed pump pumps fuel into a 2-plunger
chamber also internal to the fuel supply pump. Fuel into
this chamber is regulated by the FRP regulator solely
controlled by current supplied from the ECM. No
current to the solenoid results in maximum fuel flow
whereas full current to the solenoid produces no fuel
flow. As the engine spins, these two plungers produce
high pressure in the fuel rail. Since the ECM controls
the flow of fuel into this 2-plunger chamber, it therefore
controls the quantity and pressure of the fuel supply to
the fuel rail. This optimizes performance, improves
Delivery valve
Fuel rail
Return
Fuel overflow
Driveshaft
Suction valve
Plunger
Return spring
Priming pump
economy and reduces NOx emissions.
Suction pressure
Feed pressure
High pressure
Return pressure
FRP regulator
Regulation valve
Feed pump
Fuel inlet
Suction
Fuel filter
LNW81AMF000601