Isuzu N-Series. Manual - part 381

6C-2 FUEL SYSTEM

GENERAL DESCRIPTION

Caution

When working on the fuel system, there are several
things to keep in mind:

• Any time the fuel system is being worked on, dis-

connect the negative battery cable except for those
tests where battery voltage is required.

• Always keep a dry chemical (Class B) fire extin-

guisher near the work area.

• Replace all pipes with the same pipe and fittings

that were removed.

• Clean and inspect “O” rings. Replace where re-

quired.

• Always relieve the line pressure before servicing

any fuel system components.

• Do not attempt repairs on the fuel system until you

have read the instructions and checked the pic-
tures relating to that repair.

Description

Fuel Filters
The Purpose of the fuel filters is to clean the fuel of any
dirt particles that can cause wear on the fuel injection
nozzle’s sliding surface; and to separate any water from
the fuel, which is ever-present from the condensation in
the fuel tank. The pre-fuel filter (water separator) is lo-
cated between the fuel tank and the injection pump. The
secondary fuel filter is located between the fuel pump
and the injection pump.
Pre-Fuel Filter
When the condensed water in the pre-fuel filter (water
separator) comes to the warning level indicated on its
plastic body, drain the fluid immediately from the drain
plug located bottom of water separator.
Injection Pump
The fuel injection system includes a fuel tank, fuel hoses
and lines, a fuel/water separator, fuel filters, a fuel
pump, a Bosch-type in-line fuel injection pump with an
internal governor, delivery valves, fuel injection lines
and for fuel injection nozzles.
The fuel pump, injection pump and the nozzle are man-
ufactured by Bosch AS corporation, but serviced by
Bosch.
Remove the injection pump and governor assembly as
a unit to have it services. Do not open or break any seals
on the pump or the warranty is void. The injection pump
has an identification plate attached to the pump body.

FUEL SYSTEM 6C-3

Fuel Flow

Legend

A. Feed

3. Fuel tank

B. Return

4. Fuel filter

1. Nozzle

5. Injection pump

2. Water separator

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6C-4 FUEL SYSTEM

4HF1-2

Aneroid Compensator Function
The bellows in the aneroid compensator is provided with
an initial set force by the aneroid compensator spring
and is compressed by the push rod C. As the atmo-
spheric pressure drops, the bellows begins to expand
against the force of the aneroid compensator spring,
which in turn causes the push rod B, through the push
rod C and the boost compensator lever F, to move to the
left.
Then the push rod B comes into contact with the U-
shaped lever and, as the expanding bellows over come
the force of the cancel spring installed on the U-shaped
lever, causes the U-shaped lever to turn clockwise. Be-
cause the bottom of the sensor lever is in touch with the
torque cam, the torque cam then works as a pivot on
which the top of the sensor lever moves to the right to-
gether with the U-shaped lever. At the same time, the
control rack, which is hooked on the sensor lever,
moves toward the governor to reduce fuel injection.

Legend

1. Engine

4. Injection pump

2. Leak off pipe

5. Fuel filter (sedimeater)

3. Nozzle

6. Fuel tank

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FUEL SYSTEM 6C-5

Brief Explanation of Emission and Electri-
cal Control System

MITICS (Mechanically Integrated Timing and In-
jection Control System)

4HE1-TC
The Mechanically Integrated Timing and Injection rate
Control System (MITICS) utilizes mechanical control, in
comparison with TICS systems, which utilize electronic
control.
MITICS is equipped with the RLD-M type governor,
which contains a pre-stroke control mechanism. With
this, pre-stroke position (i.e, beginning of static injection)
can be varied to control injection timing and injection
rate (i.e., the fuel injection quantity injected from the
nozzle per cam angle degree).
This enables high injection rates1 in the low and medi-
um speed ranges through a short injection interval, thus
contributing to higher engine torque and cleaner ex-
haust.

MITICS was developed in response to the demands of
medium sized diesel engines for low cost, low fuel con-
sumption, high output and cleaner emissions.
High injection rates using a short injection interval.

• The speed at which the injection pump plunger ris-

es slows as engine speed decreases and the pres-
sure inside the injection pipe decreases. Because
of this, the nozzle spray deteriorates and makes it
impossible to obtain the proper fuel - air mixture.
To obtain the proper mixture at low and medium
speeds, it is necessary to increase the pressure in-
side the injection pipes using a short injection inter-
val.

Legend

1. Control rack

7. Full load set screw

2. Sensor lever

8. Boost compensator lever

3. U-shaped lever

9. Aneroid compensator spring

4. Torque cam

10. Bellows

5. Push rod B

11. Return spring

6. Cancel spring

12. Push rod C

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