Isuzu N-Series. Service manual - part 736

6E-366 Engine Control System (4HK1)

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 engine control module (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.

Flow Damper

Legend

1. Orifice
2. Slit
3. Piston
4. Return Spring
5. Housing
6. Fuel Rail
7. Injector

The flow dampers are installed at the outlet of fuel rail
to damp a pulsation of fuel pressure inside the fuel rail
or to cut off the fuel supply when the fuel leaks
downstream of flow damper. The fuel is supplied to the
injectors through an orifice of the piston. The pressure
pulsation occurring in the fuel rail is dampered by a
resistive force of the return spring and a passing
resistance of the orifice, wherein the piston acts as a
damper. Also, the leading end of piston closes the fuel
supply port to cut off the fuel supply, if the fuel leak
occurs in the injection pipe or injectors. Since fuel
pressure on the downstream side of flow damper
supplied through an orifice + resistive force of return
spring do not balance, the fuel pressure applied on the
piston surface prior to the orifice will allow the fuel to be
cut off. The piston will return when the fuel pressure
inside the fuel rail is less than 1.0 MPa (145 psi).

Fuel Rail Pressure Sensor
Refer to Engine Control Component Description.

Pressure Limiter

Legend

1. Valve
2. Valve Body
3. Valve Guide
4. Spring
5. Housing
6. Fuel Rail
7. Fuel Return Pipe

The pressure limiter relieves pressure by opening the
valve if abnormally high pressure is generated. The
valve opens when pressure in rail reaches
approximately 200 MPa (29,000 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.

N6A6500E

N6A6501E

Engine Control System (4HK1) 6E-367

Fuel Rail Pressure (FRP) Regulator

Legend

1. Fuel Temperature (FT) Sensor
2. Fuel Rail Pressure (FRP) Regulator

The engine control module (ECM) controls the duty
ratio of the linear type fuel rail pressure (FRP) regulator
(the length of time that the current is applied to the FRP
regulator), in order to control the quantity of fuel that is
supplied to the high-pressure plungers. Since only the
quantity of fuel that is required for achieving the target
rail pressure is drawn in, the drive load of the supply
pump is decreased.
When current flows to the FRP regulator, variable
electromotive force is created in accordance with the
duty ratio, moving the armature to the left side. The
armature moves the cylinder to the left side, changing
the opening of the fuel passage and thus regulating the
fuel quantity. With the FRP regulator OFF, the return
spring contracts, completely opening the fuel passage
and supplying fuel to the plungers (Full quantity intake
and full quantity discharge). When the FRP regulator is
ON, the force of the return spring moves the cylinder to
the right, closing the fuel passage (normally opened).
By turning the FRP regulator ON/OFF, fuel is supplied
in an amount corresponding to the actuation duty ratio,
and fuel is discharged by the plungers.

Fuel Injection Quantity Control Description

Fuel Injection Quantity Control
This control determines the fuel injection quantity by
adding coolant temperature, fuel temperature, intake
air temperature, barometric pressure, vehicle speed
and some switch inputs information corrections to the
basic injection quantity is calculated by the engine
control module (ECM) based on the engine operating
conditions (engine speed, accelerator pedal pressing
amount and boost pressure sensor). More fuel rate
indicates if the engine load is increased as the
accelerator pedal is stepped on at constant engine
speed.
Combined with high pressure injection of atomized fuel,
this control improves exhaust gas and ensures proper
fuel consumption. Compared with conventional
mechanical governors, an electronic control system
provides higher degree of freedom of fuel injection
quantity control, thereby presenting high accelerator
response (acceleration feeling and pressing feeling).

Starting Injection Quantity Control
At the engine starting (after the key switch is turned to
the START position to start the engine, up to return of
key switch to the ON position), optimum fuel injection
quantity is controlled based on the information on the
engine speed and coolant temperature. At low
temperature, the fuel injection quantity increases.
When the engine started completely, this boosted
quantity mode at the starting is cancelled and normal
running mode is restored.

Idle Speed Control
A control is made so as to achieve stable idling speed
at all time regardless of engine secular changes or
engine condition variations. The ECM sets target idling
speed and controls the fuel injection quantity according
to the engine conditions (actual engine speed, coolant
temperature and engine load) to follow actual engine
speed to the target idling speed so as to ensure stable
idling speed.

Idle Vibration Control
A control is made so as to reduce the engine vibration
caused by torque variations between cylinders due to
variations in fuel injection quantity of each cylinder or
injector performance. The ECM corrects the injection
quantity between cylinders based on the revolution
signals from the crankshaft position (CKP) sensor.
Normal range of correction quantity between cylinders
is within

± 5 mm

N6A6492E

6E-368 Engine Control System (4HK1)

Fuel Injection Timing Control Description

The injection timing suitable for the vehicle conditions is
controlled based on the inputs from respective sensors.
The injection timing is determined by comparing
actually measured values of pulse signals from the
CKP sensor with the target injection timing stored in the
map of the ECM.

Coolant Temperature Compensation
At the engine starting when the engine coolant
temperature is low, the coolant temperature is detected
to advance the injection timing for reduction of white
smoke emission.

High Altitude Compensation
During running at a highland where air density is low,
the atmospheric pressure is detected to advance the
injection timing for reduction of white smoke emission.

Exhaust Gas Recirculation (EGR) System
Description

Legend

1. EGR Cooler
2. ECM
3. EGR Valve

The EGR system recirculates a part of exhaust gas
back into the intake manifold, which results in reducing
nitrogen oxide (NOx) emissions. The EGR control
system uses an electronic control system to ensure
both driveability and low emission. The control current
from the engine control module (ECM) operates the
motor to control the lift amount of EGR valve. Also, an
EGR position sensor is provided at the rear of the
motor to feed actual valve lift amount back to the ECM
for more precision control of the EGR amount.

The EGR control starts when the conditions for engine
speed, engine coolant temperature and barometric
pressure are satisfied. Then, the valve opening is
calculated according to the engine speed, and target
fuel injection quantity. Based on this valve opening, the
drive duty of the motor is determined and the motor is
driven accordingly.
A potentiometer type EGR valve position sensor is
employed and installed on the EGR valve body. The
EGR valve position sensor is supplied with reference
voltage (5V) and ground at all times from the ECM. The
ECM reads the EGR position sensor voltage input and
determines the EGR lift position.

Turbocharger Description

Legend

1. Exhaust Gas
2. Clean Air
3. Turbine Wheel
4. Compressor Wheel
5. Air Cleaner
6. Charge Air Cooler (Intercooler)
7. Wastegate Valve

The turbocharger is used to increase the amount of air
that enters the engine cylinders. This allows a
proportional increase of fuel to be injected into the
cylinders, resulting in increased power output, more
complete combustion of fuel, and increased cooling of
the cylinder heads, pistons, valves, and exhaust gas.
This cooling effect helps extend engine life.
Heat energy and pressures in the engine exhaust gas
are utilized to drive the turbine. Exhaust gas is directed
to the turbine housing. The turbine housing acts as a
nozzle to direct the shaft wheel assembly. Since the
compressor wheel is attached directly to the shaft, the
compressor wheel rotates at the same speed as the
turbine wheel. Clean air from the air cleaner is drawn
into the compressor housing and wheel. The air is
compressed and delivered through a crossover pipe to

N6A6502E

N6A6503E

Engine Control System (4HK1) 6E-369

the engine air intake manifold, then into the cylinders.
The amount of air pressure rise and air volume
delivered to the engine from the compressor outlet is
regulated by a waste gate valve in the exhaust housing.
The position of the waste gate valve is controlled by the
amount of pressure built up on the intake side of the
turbocharger. The diaphragm on the inside of the waste
gate is pressure sensitive, and controls the position of
the valve inside the turbocharger. The position of the
valve will increase or decrease the amount of boost to
the turbocharger.
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 heat 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.

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