Engine JAC HFC4DA1-2C. Manual — part 18

Maintenance manual for sunray hfc4da1-2c china-IV diesel engines

71

Section II Working Principle of Low Pressure Fuel Line System

I. Composition of low pressure fuel line:

The low pressure fuel line is functioned to supply sufficient fuel to the
high pressure fuel line and is composed of:

z Fuel tank (including filter screen)

z Fuel filter (including manual fuel delivery pump)

z Low pressure fuel delivery pump

z Other low pressure fuel hoses

II. Fuel tank

The fuel tank shall be fabricated from anti-corrosion material and shall maintain 0.3bar pressure under all working
conditions and be free of fuel leakage under the application of the doubled working pressure. The fuel tank shall also
set up appropriate opening or safety valve or adopt appropriate measures to relieve the excessive pressure whenever
it's needed. When the motor vehicle is subject to slight vibration, makes turns or travels or parks on a slope, the fuel in
the fuel tank shall not leak from the fuel tank cap or the pressure balancing device.

III. Fuel filter (including manual fuel delivery pump)

Sunray long-wheelbase model adopts two-stage diesel filter, including
one primary filter and one fine filter. Compared with traditional diesel
engines, it requires cleaner fuel supply. The impurities contained in
the fuel will damage the fuel system including the high pressure pump,
high pressure common rail, and fuel injector. The fuel filter purifies
the fuel inputting into the high pressure fuel pump, in order to help the
normal functioning of the high pressure pump. The contaminant,
impurity, and particle in the fuel will lead to the damage of pump units,
fuel supply valve, and fuel injector. Therefore, the use of fuel filter
capable of meeting the fuel injector requirements becomes the
premise for normal working of the engine and guarantee of service life.
The water content in the diesel may exist in non-free radical form
(emulsified fuel) or radical form (such as water condensate generated
due to variation of temperature). If entering into the fuel injection
system, this water content will lead to damage of parts due to corrosion.
Similar to other fuel injection systems, common rail system requires
the fuel filter with water collection chamber as well as the automatic
water content alarm. When the alarm lamp lights up, make sure to
drain the water from the water collection chamber.

The fuel filter is composed of fuel temperature sensor, fuel heater,

manual fuel pump, fuel-water separator, and water level sensor.
The fuel leakage during traveling or the air ingress into fuel pipeline
after replacement of fuel filter may lead to start failure or poor
functioning of the engine. Therefore, make sure to bleed the air from
the low pressure fuel pipeline after the installation of manual fuel
delivery pump. Installed on the fuel filter, the manual fuel delivery
pump is the device for supplying fuel to the fuel filter and the device
required to guarantee the first start of the engine. In event of the
following conditions, press the manual fuel delivery pump, till the
manual fuel delivery pump can’t be further pressed, before starting the

Maintenance manual for sunray hfc4da1-2c china-IV diesel engines

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engine.

z After the fuel is used up.

z After the water drainage from the fuel-water separator.

z After the replacement of fuel filter

Replacement of fuel filter

1. Replacement interval of fuel filter: Once every 7,000km;

2. Water separation interval: Once every 5,000Km;

3. It’s prohibited to use any used fuel filter.

IV. Low pressure fuel delivery pump

The low pressure fuel delivery pump is one gear pump and is stalled
at the rear end within the high pressure pump housing. The low
pressure fuel delivery pump continually supplies the required fuel
amount to the high pressure pump from the fuel tank.

The fuel delivery pump is functioned to supply sufficient fuel
supply to the high pressure pump under following conditions:

(1) Under any working condition;

(2) Under necessary pressure;

(3) Throughout the entire service life.

The low pressure fuel delivery pump is one mechanical gear pump and is installed at the rear end of high pressure
pump and driven by the high pressure pump shaft. Its main parts are two gears rotating in opposite direction. While
rotating, two gears engages to vacuumize the fuel into the chamber formed between gears and pump walls and then
conveys to the outlet (pressure end). The closing line of the rotating gears realizes the sealing between vacuumization
end and pressure end of the pump and prevents the fuel backflow.
The fuel supply amount of the gear pump is approximately in proportion to the engine speed. This is why the fuel
supply amount of the gear pump can be reduced by means of the throttle valve at the inlet end or can be restrained by
means of the relief valve at the outlet end.
No maintenance is required for the gear pump. Charge the fuel from the fuel system before the first start. When the
fuel in the fuel tank is used up, operate the manual fuel delivery pump to charge fully the low pressure fuel line.

V. Fuel pipeline

Besides the steel pipe, the low pressure fuel line can also adopt flame-retardant braided and armored fuel hose. The
fuel pipes shall be arranged in such manner to prevent the mechanical damage and that the fuel dripped or evaporated
will not concentrate nor burn.

In event of vehicle distortion, engine displacement, or similar conditions, the functions of the fuel pipeline shall not be
impaired. All fuel delivery pipelines shall have the radiation shield measures.

Maintenance manual for sunray hfc4da1-2c china-IV diesel engines

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VI. Common malfunctions and troubleshooting for low pressure fuel line

No. Malfunction

Troubleshooting

Remarks

1

Weak pumping of
fuel

Retighten the connectors (temperature
sensor, plug, and pile connector), in
order to prevent the pumping failure
due to ingress of air. If ineffective,
replace the manual pump.

The tightening torque for connectors is
30-35N.m. Higher torque will lead to
thread failure.

2

Fuel leakage of air
bleeding screw

Check the screw hole of manual pump
for presence of thread failure. If yes,
replace the transitional thread insert
and air bleeding screw and washer.

The tightening torque is 7~9N.m. Higher
torque will lead to thread failure. While
assembling the transitional thread insert,
add an appropriate amount of thread sealant
onto the thread. Prevent the ingress of
sealant into the manual pump.

3 Fuel

leakage

of

manual pump

Replace the manual pump

The knocking or improper use will lead to
fuel leakage of manual pump

4 Slow

acceleration

and difficult start
due to difficult
fuel supply

The filter is blocked. Replace the filter.
If the malfunction still occurs after
replacement of fuel filter, check other
engine parts.

The blockage of fuel filter will increase the
pressure difference.

5

Failure for timely
water drainage

Make sure to drain the water when the
water level sensor indicator lamp lights
up.

If the water is not drained, the water
content in fuel will increase to impair the
engine performance.

6

Light-up failure of
water level sensor
indicator lamp at
engine start

1. Water level sensor is damaged.

2. Indicator lamp is damaged.

3. Circuit malfunction

7

Working failure of
heater

1. The heater is damaged.

2. Circuit malfunction

3. Low battery current

4. The heater is punctured due to high
current

8

Working failure of
temperature
sensor

Damage o temperature sensor

Circuit malfunction

Maintenance manual for sunray hfc4da1-2c china-IV diesel engines

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Section III Working Theory of High Pressure Fuel Line

I. High pressure fuel line parts

The high pressure fuel line generates and accumulates
sufficient fuel pressure required for the fuel injectors.
The parts include: High pressure pump, fuel rail, high
pressure fuel pipe, and fuel injector.

II. High pressure pump

The high pressure pump compresses the fuel to a system
pressure of up to 1,450bar and then the fuel is
transmitted to the tubular high pressure fuel accumulator
(rail) via the high pressure pipe.

The high pressure pump is the interface between low pressure stage and high pressure stage. Under all working
conditions, it can reliably supply sufficient high pressure fuel throughout the entire service life of the vehicle,
including supplying addition fuel required for rapid start and the
rapid establishment of pressure in the common rail. The high
pressure pump continually generates the system pressure required
for the high pressure accumulator (rail). Therefore, it means that,
compared with traditional system, it’s unnecessary to compress the
fuel for each individual injection cycle.

The fuel is compressed by three plunger pumps arranged radially at
spacing of 120º from each other. As each rotation turn can generate
three compression strokes and only generate low peak drive torque,
the drive unit of the pump maintains uniform force application. As
far as 16Nm torque is concerned, this torque is only 1/9 of the
torque required for driving similar distribution pump. This means
that, compared with traditional fuel injection systems, the common rail generates lower load onto the drive unit of the
pump. The raising power of the drive pump is in proportion to the preset pressure of common rail and the speed of the
fuel pump (fuel delivery amount).

Working mode:

Through one water separator, the fuel delivery pump pumps out the fuel from the fuel tank and the fuel enters into the
lubricating and cooling lines of high pressure pump via the fuel inlet. The drive shaft with eccentric wheel drives three
pump plungers for upward and downward movements along with the profile of the cam. The pump plungers move
downward under the application of the fuel delivery pressure (fuel suction stroke). When the plungers overpass the
bottom dead center, the fuel inlet valve is closed so that the fuel in the pump chamber will not leak out. In such case,
the fuel is compressed so that the fuel pressure exceeds the fuel delivery pressure of the fuel delivery pump. In such
case, once the pressure established exceeds the pressure in the common rail, the fuel outlet valve opens so that the fuel
enters into the high pressure line. The pump plungers will continue the fuel supply, till the top dead center is reached
(fuel delivery stroke). Then the pressure drops and the fuel outlet valve closes. The residual fuel is pressure relieved:
The pump plungers move downward. When the pressure in the pump chamber is less than the fuel delivery pressure,
the fuel inlet valve re-opens and the pumping process is started again.

III. Fuel rail (Common rail)

The high pressure accumulator (rail) stores the high pressure fuel and at the same time restrains the pressure variation
generated during the fuel supply and fuel injection of the high pressure pump. The high pressure accumulator is
shared by all cylinders and therefore is referred to as “common rail”. Even when a great amount of fuel is drained, the
common rail can maintain its internal pressure basically unchanged. Therefore it maintains the constant fuel injection
pressure of the fuel injector.

1.

Drive shaft

2.

Eccentric cam

3.

Plunger pump

4.

Fuel suction valve

5.

Fuel outlet valve

6.

Fuel inlet