Isuzu N 2008 Series Workshop Manual page 374

Engine Control System (4JJ1) 1A-371
The amount of air pressure rise and air volume
delivered to the engine from compressor outlet is
regulated by a turbocharger nozzle control actuator
indirectly. The position of the turbocharger nozzle is
controlled by the ECM. The ECM utilizes a
turbocharger nozzle control solenoid valve and a boost
pressure sensor to control the turbocharger nozzles.
When the engine is not under load, the turbocharger
nozzles are in an open position (A), or no boost
condition (vacuum pressure supply to the actuator is
reduced). When the engine is under load, the ECM
commands the control solenoid valve to close the
turbocharger nozzles (B), thus increasing the boost
(vacuum pressure supply to the actuator is increased).
The ECM will vary the boost dependant upon the load
requirements of the engine. The ECM uses a pulse
width modulation (PWM) on the control circuit to open
and control the solenoid valve. (Euro 4 specification)
The charge air cooler also helps the performance of the
diesel. Intake air is drawn through the air cleaner and
into the turbocharger compressor housing. Pressurized
air from the turbocharger then flows forward through
the charge air cooler located in the front of the radiator.
From the charge air cooler, the air flows back into the
intake manifold.
The charge air cooler is a heat exchanger that uses air
flow to dissipate hear from the intake air. As the
turbocharger increases air pressure, the air
temperature increases. Lowering the intake air
temperature increases the engine efficiency and power
by packing more air molecules into the same space.