Isuzu KB P190. Manual - part 494

ENGINE CONTROL SYSTEM (4JK1/4JJ1)   6E-359

Mass Air Flow (MAF) Sensor

The MAF sensor is an air flow meter that measures the
amount of air that enters the engine. It is fitted between
the air cleaner and turbocharger. A small quantity of air
that enters the engine indicates deceleration or idle
speed. A large quantity of air that enters the engine
indicates acceleration or a high load condition. The
MAF sensor assembly consists of a MAF sensor
element and an intake air temperature (IAT) sensor that
are both exposed to the air flow to be measured. The
MAF sensor element measures the partial air mass
through a measurement duct on the sensor housing.

Fuel System Description

The common rail system uses a type of accumulator
chamber called the fuel rail to store pressurized fuel,
and injectors that contain electronically controlled
solenoid valves to spray the pressurized fuel in the
combustion chambers. The injection system (injection
pressure, injection rate, and injection timing) is
controlled by the ECM, and therefore the common rail
system can be controlled independently, free from the

influence of engine speed and load. This ensures a
stable injection pressure at all time, particularly in the
low engine speed range, so that black smoke specific
to diesel engines generated during vehicle starting or
acceleration can be reduced dramatically. As a result,
exhaust gas emissions are clear and reduced, and
higher output is achieved.

AAW46ESH001401

RTW76EMF000401

Supply pump

One-way valve

Fuel tank

Fuel filter

Camshaft

position

sensor

Crankshaft

position

sensor

Various sensors

(accelerator position sensor, coolant temperature,

mass air flow, etc.)

Injectors

Pressure sensor

Fuel rail

Pressure

limiter valve

ECM

6E-360   ENGINE CONTROL SYSTEM (4JK1/4JJ1)

1. High Pressure Control

• Enables high pressure injection from low engine

speed range.

• Optimizes control to minimize particulate matter

and NOx emissions.

2. Injection Timing Control

• Enables finely tuned optimized control in

accordance with running conditions.

3. Injection Rate Control

• Pilot injection control that performs a small amount

of injection before main injection.

The fuel rail system consists primarily of a fuel supply
pump, fuel rail, injectors, and ECM.

Fuel System Component Description

Injector

Legend

1. Fuel injector ID code
2. Leak off pipe
3. Two dimensional barcode
4. Port for mounting the injection pipe
5. O-ring

 

Electronic control type injectors controlled by the ECM
are used. Compared with conventional injection
nozzles, a command piston, solenoid valve, etc. are
added.
ID codes displaying various injector characteristic are
laser marked on the connector housing, and ID codes

showing these in numeric form (24 alphanumeric
figures). This system uses fuel injector flow rate
information (ID codes) to optimize injection quantity
control. When an injector is newly installed in a vehicle,
it is necessary to input the ID codes in the ECM.
QR (Quick Response) codes or fuel injector flow rate
(ID codes) have been adopted to enhance the injection
quantity precision of the injectors. The adoption of
codes enables injection quantity dispersion control
throughout all pressure ranges, contributing to
improvement in combustion efficiency and reduction in
exhaust gas emissions.

RTW56EMH000101

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ENGINE CONTROL SYSTEM (4JK1/4JJ1)   6E-361

1) Non-injection state

The two way valve (TWV) closes the outlet orifice by
means of a spring force, when no current is supplied
from the ECM to the solenoid. At this time, the fuel
pressure applied to the nozzle leading end is equal to
the fuel pressure applied to the control chamber
through the inlet orifice. As for the force competition in
this state, the pressure on the command piston upper
surface + nozzle spring force defeat the pressure on
the nozzle leading end, and consequently the nozzle is
pushed downward to close the injection holes.

2) Injection start

The TWV is pulled up to open the outlet orifice, and
thus the fuel leaks toward the return port, when the
current is supplied from the ECM to the solenoid. As a
result, the nozzle is pushed up together with the
command piston by the fuel pressure applied to the
nozzle leading end, and then the nozzle injection holes
open to inject the fuel.

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.

RTW76EMF000601

No injection

Injection rate

Pressure in

control chamber

Pressure in

control chamber

Pressure in

control chamber

Driving current

Driving current

Driving current

Injection rate

Injection

Injection end

Solenoid

Outlet orifice

Inlet orifice

Command piston

Nozzle

From fuel rail

TWV

Return port

Control chamber

6E-362   ENGINE CONTROL SYSTEM (4JK1/4JJ1)

Fuel Supply Pump

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
economy and reduces NOx emissions.

Fuel Rail (Common Rail)

Legend

1. Pressure limiter valve
2. Fuel rail pressure (FRP) sensor

 

RTW76EMF000201

Suction pressure
Feed pressure

Return pressure

High pressure

Fuel rail

Injector

Delivery valve

Cuction valve

Plunger

Fuel inlet

Regulation valve

Driveshaft

Fuel overflow

Feed pump

Return spring

Fuel tank

Fuel filter

Return

Suction

FRP regulator

RTW76ESH002001

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