Isuzu N-Series. Manual - part 382

6C-6 FUEL SYSTEM

• The following figure shows plunger speed and cam

lift in relation to cam angle. It can be seen from the
graph that plunger speed increases together with
cam lift.
MITICS varies the beginning of injection position at
low and medium speeds so that injection occurs
when the plunger speed increases during the latter
half of cam lift (shown by the bold line). At high
speeds, injection is performed when the plunger
speed decreases during the first half of cam lift to
prevent an excessive increase in injection pipe
pressure.
This enables high pressures at low and medium
speeds with a fast plunger speed. Thus, a fine fuel
oil spray is injected into the cylinder from the noz-
zles within a short time to provide the proper mix-
ture for combustion, helping to increase torque and
keep exhaust emissions clean.

Governor (Model RLD-M)

4HE1-TC
The RLD-J type governor can be used with the MI,
MITICS injection pumps, and was designed to have bet-
ter control and endurance than the previous RLD type
governor.
Although the basic construction is identical to that of the
RLD type governor, the RLD-M type is larger to match
the applicable pumps’ larger size.
Features

1. Variable speed control governor with decreased le-

ver reaction force
As with the previous RLD type governor, RLD-M
governor control is accomplished using the speed
control lever to change the fulcrum of the internal
link mechanism.
Consequently, as the reaction force of the gover-
nor spring does not act directly on the speed con-
trol lever, only a very small lever reaction force is
exerted on the accelerator pedal.

Legend

1. Injection pipe pressure
2. PE-AD type injection pump
3. Engine speed

N6A0820E

Legend

A. Plunger speed
B. Cam lift

1. Plunger speed (m/sec)
2. Cam lift (mm)
3. Cam angle (degrees)

N6A0821E

FUEL SYSTEM 6C-7

2. Set torque characteristics through internal torque

cam
At full load, the tip of the sensor lever traces the
face of the torque cam to determine the full load
rack position and control the full load injection
quantity.
Consequently, the torque characteristics demand-
ed by the engine can be freely set by changing the
shape of the torque cam face.

3. Improved control through internal guide plate

When the speed control lever is operated, the 2nd
supporting lever’s pin moves along the guide plate.
The floating lever connected to the pin thus moves
to change the ball joint fulcrum positions. In the in-
termediate to high speed ranges, the guide plate
causes the floating lever to move to increase the
lever ratio continuously from 1.1 (idling) — 6 (full
speed). This increase in the lever ratio in the inter-
mediate to high speed range improves speed
droop.

Injection Nozzle

A Bosch hole type injection nozzle is used. It consists of
the nozzle body and the needle valve assembly.
The injection nozzle assembly sprays pressurized fuel
from the injection pump into the combustion chamber
through the nozzle body injection orifice.

Legend

1. At maximum speed control
2. At idle speed control
3. Speed control lever
4. Governor spring
5. Link mechanism

N6A0822E

N6A0823E

Legend

1. Sensor lever
2. Torque cam
3. Control rack position (mm)
4. Pump speed (r/min)

Legend

1. Ball joint
2. Floating lever
3. 2nd supporting lever pin
4. Speed control lever
5. Guide plate

N6A0824E

6C-8 FUEL SYSTEM

Fuel Filter and Water Separator

A cartridge type fuel filter and a water separator are
used along with the in-line type injection pump.
As the inside of the injection pump is lubricated by the
fuel which it is pumping, the fuel must be perfectly clean.
The fuel filter and the water separator remove water par-
ticles and other foreign material from the fuel before it
reaches the injection pump.
The water separator has an internal float. When the float
reaches the specified level, a warning light comes on to
remind you to drain the water from the separator.

N6A0825E

Legend

1. Body assembly
2. Filter cartridge
3. Case
4. Lever sensor
5. Drain plug

N6A0826E

FUEL SYSTEM 6C-9

FUEL FILTER ASSEMBLY (Except 4HF1-2 model)

Component

Removal

Preparation

• Disconnect battery ground cable.
• Tilt the cab

1. Fuel Pipe
2. Fuel Filter Assembly

Installation

1. Fuel Filter Assembly

Tighten:
Fuel filter bracket to 34 N

⋅m (3.5 kg⋅m / 25 lb⋅ft)

2. Fuel Pipe

Tighten:
Fuel pipe joint bolt to 23 N

⋅m (2.4 kg⋅m / 17 lb⋅ft)

Air Bleeding

• Loosen the priming pump cap (1).
• Loosen the air bleeding plug. (4HG1-T model only)
• Operate the priming pump.

Pump the primer pump until fuel flow is free of air
bubbles. (Except 4HG1-T model)

• Tighten the air bleeding plug. (4HG1-T model only)
• Loosen the bleeding plug.
• Operate the priming pump.

Pump the primer pump until fuel flow is free of air
bubbles.

• Tighten the bleeder plug.
• Operate the priming pump.

Pump the primer pump until fuel flow is free of air
bubbles. (Except 4HE1-TC model)

• Loosen the bleeding plug on the injection pump (2).

(4HE1-TC model only)

• Operate the priming pump.

Pump the primer pump until fuel flow is free of air
bubbles. (4HE1-TC model only)

• Tighten the bleeding plug on the injection pump

(2). (4HE1-TC model only)

• Lock the priming pump cap (1).

Notice:
Check for fuel leakage from around the injection pump
and the fuel filter.

Legend

1. Fuel pipe

2. Fuel filter

N6A0827E