JAC HFC4DA1-2C engine. Instruction — part 6

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

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2) Working Principle

This sensor is composed of two sensors, namely airflow sensor and intake temperature sensor, and is installed on the
intake hose after the air cleaner. This type of sensor requires that there shall be free of air leakage from the sensor to
the engine combustion chamber, or it will lead to unstable idling of engine or even engine flameout.

The airflow sensor integrates some micro-electronic units on a ceramic substrate. When the engine is working, the
diaphragm will be heated. The intake airflow passing through the diaphragm will take away the heat and the
Wheatstone bridge integrated on the diaphragm will increase the current to supplement the heat loss, which leads to
the variation of electric signal. This signal is transmitted to the engine control unit ECU, based on which the ECU can
obtain the load variation of the engine and thus control the fuel injection pulse width.

The intake temperature sensing unit is one negative temperature coefficient (NTC) thermistor. The sensor installs two
same sensing units on two sides of the thermal diaphragm. When the intake airflow flows through the diaphragm, the
temperature of the temperature sensing unit on the front of diaphragm is slightly lower than that of temperature
sensing unit on the rear. Based on this characteristic, the ECU can judge the direction of airflow.

3) Measurement analysis

Wiring terminals: 1. +12V power supply; 2. Grounding; 3. Air temperature signal; 4. Airflow rate signal.

4) Malfunction Mode

The subsequent electronic device of the air flowmeter in the ECU can judge the malfunctions such as open-circuit or
short-circuit of internal circuit and connecting circuit of air flowmeter and the damage of sensor. Upon the detection
that the output signal of the sensor is out of its output characteristic curve, the ECU will judge as malfunction of
sensor.

5) Troubleshooting

When the airflow sensor is failed, the engine cooling fan will run at high speed for one period after the ignition key is
turned to Off. For instance: When the airflow rate is higher than the upper limit of airflow or less than the lower limit
of airflow, the ECU will judge as malfunction of sensor (Though the intake airflow rate is less than lower limit
(closing to zero) at the start of the vehicle, the ECU can judge the start condition) and at the same time light up the
engine malfunction lamp and work under malfunction mode.

Air flowmeter

Voltage output V

Common rail

pressure

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5. Rail pressure sensor

1) Overview

The resistance of the metal film installed on the diaphragm will change accordingly following the change of shape.
This change of shape generated by the established system pressure (approximate 1mm under 1,500bar pressure) will
change the resistance and lead to the change of voltage between two sides of 5V bridge composed of resistor units.
This voltage change range is 0~70mv (depending on the applied pressure) and is amplified to 0.5~4.5V by the
evaluation circuit.
The accurate measurement of rail pressure is of great importance to the effective working of the system. This is one of
the causes for very strict tolerance over the rail pressure sensor during the pressure measurement. Under the scope of
main working conditions, the measurement accuracy is approximately ±2% of the full scale reading.

Wiring terminals: 1. Grounding; 2. Rail pressure sensor signal; 3. +5V power supply.

2) Working Principle

It transmits one voltage signal to the ECU, depending on the fuel pressure. The rail pressure sensor must measure the
instant pressure in the fuel rail and embody sufficient accuracy and rapid response capability. The rail pressure sensor
is composed of following parts:
cIntegrated sensing unit welded onto the pressure device
d Printed circuit board (PCB) with electric evaluation circuit
sensor housing with electric connector. The fuel flows into the rail pressure sensor via one hole on the common rail
and the end of this hole is sealed by one sensor diaphragm. The fuel under high pressure reaches the sensor diaphragm
via one blind hole. One sensing unit (semiconductor unit) is arranged on this diaphragm and converts the pressure into
electric signal. This signal generated is transmitted via wire to evaluation circuit, which will amplify this signal and
transmit to the ECU.

3) Test analysis

Wiring terminals: 1 - Grounding; 2 - Rail pressure sensor signal; 3 - +5V power supply.

4) Malfunction Mode

The malfunction indicator lamp lights up if the voltage is higher or less than this limit. If the voltage is out of the
normal working voltage range, but is not out of the limit, the malfunction indicator lamp will not light up.

5) Troubleshooting

The light-up of the engine malfunction indicator lamp indicates the presence of malfunction in the engine system and
it’s necessary to diagnose with diagnosis instrument. Use JAC special diagnosis instrument to communicate with ECU
of electronic injection system and read out the malfunction data in the ECU.

6. Engine coolant temperature sensor

1) Overview

z The sensor is installed on the cylinder head, closing to the water outlet. The body is made of brass to protect the

resistor unit fabricated from negative temperature coefficient (NTC) resistor;

Rail

pressure

sensor

5V power supply

Rail sensor signal

Grounding

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z The temperature resistor of the temperature sensor is one part of the 5V

voltage division circuit. Two terminals of the temperature sensor is
connected with the voltage charged circuit. When the temperature
resistor of the temperature sensor changes along with the temperature,
the voltage of the voltage charged circuit changes accordingly, which
will be inputted to the analog/digital conversion circuit of ECU
interface circuit. The relationship characteristic curve between voltage
and temperature is stored in the ECU of engine management system;

z Sunray is equipped with 3-wire water temperature sensor to save the

cost and guarantee the system unity.

2) Working Principle

The coolant temperature sensor is used to measure the working temperature of the engine. The ECU will provide the
engine with best control scheme, depending on different temperatures.

This sensor is one negative temperature coefficient (NTC) thermistor, of which the resistance reduces following the
increasing of coolant temperature in a non-linear mode. The negative temperature coefficient thermistor is installed
within one copper heat conducting sleeve. By means of one voltage division circuit, the ECU converts the resistance
change of thermistor to one varying voltage and provides to the ECU and thus monitors the change of water
temperature (internal structure of ECU).

3) Measurement analysis

Wiring terminals: 1 – Temperature signal; 2 – Grounding

Reference values: -10℃ 8.642---10.152 kΩ

20℃2.351---2.649 kΩ

80℃0.313---0.332 kΩ

4) Malfunction Mode

Upon the detection that the water temperature signal is higher or less than the limit range, the ECU will light up the
malfunction indicator lamp.

5) Troubleshooting

Sunray is fitted with one independent coolant temperature sensor to transmit the water temperature signal to the
instrument for display of instrument water temperature alarm. If the water temperature alarm indicator lamp lights up,
stop for cooling immediately. If the water temperature alarm indicator lamp lights up frequently, drive to the
authorized service station of JAC Multifunctional Commercial Vehicle Company for service.

7. Water level sensor

1) Overview

z The fuel-water separator position sensor is functioned to measure the water content in the fuel filter;

z When the water content reaches a predefined level, the ECU will control the working of the engine. This sensor

is installed on the bottom of the fuel filter;

Characteristic curve of temperature sensor

Resi

st

an

ce

Temperature

Water

temperature

sensor

To water temperature gauge

Signal terminal

Grounding

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z The fuel-water separator position sensor is installed on the bottom of the fuel filter;

z Wiring terminals: 1. Water level sensor; 2. Water level signal; 3. +12V power supply.

2) Working Principle

The grain substances are high-accuracy filtered by means of the interception and absorption of the filter medium and
the water concentrated on the filter medium is
separated by gravity force. The water separated
is deposited in the water chamber at the lower
portion of filter housing.

The water level sensor is installed at the lower
portion of water chamber. When the water level
reaches the sensing point of the sensor, the
internal circuit of sensor is actuated to output
signal to the ECU. At the same time, the signal is
transmitted to the instrument to light up the
water level alarm lamp.

3) Measurement analysis

Wiring terminals: 1 - Water level sensor; 2 - Water level signal; 3 - +12V power supply.

4) Malfunction Mode

z Short-circuit or open-circuit of sensor;

z Unstable sensor signal;

z Sensor signal is out of range.

1) Troubleshooting

Use Sunray special diagnosis instrument to check the trouble code and determine the malfunction position. Mainly
check the circuit of sensor and determine whether there is short-circuit or open-circuit between circuit and the
grounding wire, whether there is short-circuit or open-circuit to power supply, and whether the circuit is consistent
with the given pin definition.

8. Accelerator pedal position sensor

1) Overview

The accelerator pedal position sensor is mounted on
the accelerator pedal.

The accelerator pedal position sensor and the
accelerator pedal form one integral part. The
accelerator pedal position sensor internally
incorporates two same potentiometer sensors to
provide the driver’s driving demand signal to the ECU.
This process is completely same with the presently
mechanical pedal in terms of operation, in order to
adapt to the years of driving habit of the driver. Two
same sensors provide the accelerator signal to the
ECU respectively, which guarantees more safety and reliability of the system.

Wiring terminals: 1. +5V; 2. +5V; 3. Grounding of accelerator pedal 1; 4. Signal of accelerator pedal 1; 5. Grounding
of accelerator pedal 2; 6. Signal of accelerator pedal 2.

Signal terminal of

fuel-water separator

position sensor

Water level sensor of

fuel-water separator

Output vo

ltage

Full close

Full open

Open angle of accelerator pedal

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2）Working Principle

The accelerator pedal position sensor internally adopts the damping structure and internally incorporates two same
potentiometer sensors. The signal pointers of the sensors are coaxial with the pedal. When the accelerator pedal is
stepped down, the potentiometer pointer will rotate coaxially with the pedal and, following the sliding of the
potentiometer pointer, the signal terminals output different voltage or resistance signal. Two movable potentiometer
sensors with different resistances within the position sensor output different resistances. However, there is a defined
relationship between the resistances outputted by two sensors. The ECU adopts the voltage signals, instead of the
resistance signals of the sensor, in order to prevent the signal distortion caused by the voltage fluctuation of the
alternator. A comparison circuit is adopted to compare the signal voltage outputted by the sensor with the standard
voltage and the ECU adopts the comparison result to judge the movement amplitude of the pedal. The ECU compares
the signals inputted by the sensor 1 and sensor 2 and considers other sensors (engine speed, load, etc.) to jointly judge
the trueness of the signals outputted by the sensors. If the signal distortion is judged in any of two sensors, the ECU
controls the engine to actuate malfunction mode and adopt restrained driving measures.

The accelerator pedal position sensor provides one signal voltage varying along with the accelerator pedal position.
The engine control unit (ECU) will provide independent 5V reference voltage and low level reference voltage to each
accelerator pedal position sensor. When the accelerator pedal is stepped down, the signal voltage of the accelerator
pedal position sensor 1 is increased, namely from approximate 0.7V at the free position to above 4V at the fully
stepped down position. When the accelerator pedal is stepped down, the signal voltage of the accelerator pedal
position sensor 2 is increased, namely from approximate 0.3V at the free position to above 2V at the fully stepped
down position. Two data monitor mutually via control system.

3) Measurement analysis

Wiring terminals: 1 - +5V; 2 - +5V; 3 - Grounding of accelerator pedal 1; 4 - Signal of accelerator pedal 1; 5 -
Grounding of accelerator pedal 2; 6 - Signal of
accelerator pedal 2.

Working voltage of sensor: 5V

Malfunction Mode

Short-circuit or open-circuit of sensor 1;

Short-circuit or open-circuit of sensor 2;

Unstable sensor signal;

Sensor signal is out of range.

4) Troubleshooting

Use Sunray special diagnosis instrument to check the trouble code and determine the malfunction position. Mainly
check the circuit of sensor and determine whether there is short-circuit or open-circuit between circuit and the
grounding wire, whether there is short-circuit or open-circuit to power supply, and whether the circuit is consistent
with the given pin definition.

Characteristic of sensor internal structure: Two potentiometer sensors within the sensor adopt independent power
supply and independent grounding wire, which can guarantee the system safety. When one sensor is damaged, another
sensor can still work. However, the engine system has already actuated the malfunction mode in such case and the
electronic control system will adopt the restrained driving measures.

9. Vehicle speed sensor

1) Overview

The vehicle speed sensor is located at the rear portion of the transmission and is mainly functioned to provide speed
signal to the engine control unit and instruments.

Accelerator

pedal

module

Power supply of sensor 1

Signal 1

Power supply of sensor 2

Signal 2

Grounding of sensor 2

Grounding of sensor 1

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2）Working Principle

The signal of vehicle speed sensor provides vehicle speed signal to the ECU, based on which the ECU calculates the
vehicle speed. It’s internally composed of one Hall speed sensor. Please refer to the camshaft position sensor for the
working principle.

3）Measurement analysis

10. Clutch switch

1) Overview

The clutch switch is located on the upper portion of the clutch pedal and is mainly functioned for cruise control and
engine torque smoothness control.

2) Working Principle

The clutch switch is installed at the clutch pedal and transmits the operation signal of clutch pedal to the engine ECU.
Its inside is one two-pin contact switch. When the clutch pedal is stepped down, the lower central position of the
clutch switch springs out. In such case, two pins of the clutch switch are connected. When the clutch pedal is released,
two pins of the clutch switch are disconnected. Therefore, the engine can learn the operation state of the driver by
measuring the electric level (high or low) of the clutch switch signal wire.

3) Measurement analysis

4) Malfunction Mode

Short-circuit or open-circuit of sensor;

Unstable sensor signal;

Sensor signal is out of range.

5) Troubleshooting

Use Sunray special diagnosis instrument to check the trouble code and determine the malfunction position. Mainly
check the circuit of sensor and determine whether there is short-circuit or open-circuit between circuit and the
grounding wire, whether there is short-circuit or open-circuit to power supply, and whether the circuit is consistent
with the given pin definition.

Input signal

of vehicle

speed sensor

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11.Dual brake switch

1) Overview

The dual brake switch is located on the upper portion of the brake pedal and internally incorporates two independent
switches.

2) Working Principle

The brake switch monitors the action of the brake pedal and transmits the signal measured to the engine ECU. The
brake switch is equipped with two switching mechanisms, which are the main and secondary units of the brake switch.
When the signals from both units are inputted, the engine ECU will judge as normal braking signal. These switching
signals are related to the accelerator pedal and are used to control the fuel amount during the braking. This means that
the operation of accelerator pedal will not lead to malfunction when the brake pedal is stepped down, but the operation
of accelerator pedal will reduce the fuel amount when the brake pedal is stepped down.

3) Measurement analysis

12. A/C switch

1) Overview

The A/C switch is located on the A/C control panel and is mainly functioned to transmit actuation directive of A/C
compressor to the engine control unit.

2). Working Principle

A/C request is the input signal that the driver requests the working of A/C and controls the working of A/C relay as
well as the speed promotion of the engine.

3) Measurement analysis

4) Malfunction Mode:

z Short-circuit or open-circuit of signal circuit;

z Unstable signal;

z The signal is out of range.

Low pressure

High pressure

A/C switch

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5) Troubleshooting

Use Sunray special diagnosis instrument to check the
trouble code and determine the malfunction position.
Mainly check the circuit of sensor and determine whether
there is short-circuit or open-circuit between circuit and the
grounding wire, whether there is short-circuit or
open-circuit to power supply, and whether the circuit is
consistent with the given pin definition.

II. Engine control unit (ECU)

1) Overview

The engine control unit is located on the firewall on the
back of the bottom of the glove box.

2) Working Principle

The ECU has one metal housing and the sensors, actuators, and power supply are connected to the ECU via multi-pole
plug. The power supply parts for direct control of actuators are integrated in the ECU so that their heat can be
effectively expanded to the ECU housing.

Requirements for ECU are as below:

- Surrounding (ambient) temperature: -40ºC~+85ºC

- Resistance to fuel, lubricating oil, etc.

- Resistance to moisture.

- The mechanical load has high requirements of the exposure to electromagnetic compatible (EMC) signal.

The ECU is used to calculate the signal received from the external sensors and control at the allowable voltage level.
Based on these input data and stored characteristic graph, the microprocessor can calculate out the duration and
accurate moment for fuel injection and convert into time-signal curve. The specific accuracy requirement and high
dynamic response of engine require high level calculation capability.
The driver stage is actuated by means of the output signal and supplies proper power to the actuators to control the
common rail pressure and the high pressure pump units. In addition, the actuators can control the engine functions
(such as relays for exhaust gas recirculation actuator, turbocharger pressure actuator, and electronically controlled fuel
pump) and other auxiliary functions (such as fan relay, auxiliary heater relay, and electric heating plug relay, and air
conditioner). The driver stage has the short-circuit protection and the protection against damage due to current
overload. These types of malfunctions and the open-circuit will be reported to the microprocessor. The diagnosis
function of the fuel injector driver stage can identify the error signal curve occurred. In addition, one series of output
signal can be transmitted to other vehicle systems via different interfaces. Within the specific safety concept
framework, the ECU can monitor the entire injection system.
The actuation of fuel injector advances special requirements over the driver stage. Within the fuel injector, the current
from the driver stage generates one magnetic field force in the magnetic coil that applies onto the hydraulic high
pressure system. To ensure the accurate tolerance and high repeatability of the fuel injection amount, this coil must be
actuated in front of a steep current wave. This requires ECU to form high voltage.

The actuation time (fuel injection duration) can be classified by the current control circuit into start current stage and
holding stage. It must work accurately to ensure that the fuel injectors can guarantee the repeatability of fuel injection
under all working conditions. In addition, it must reduce the energy loss in the ECU and the fuel injectors.

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3) Measurement analysis

Interface A

Interface K

Definition for ECU pins of EDC17 control system:

Terminal

No.

Description

Terminal

No.

Description

Interface A

A01

High fuel injector of 3

rd

cylinder

A31

Low fuel injector of 2

nd

cylinder

A02

High fuel injector of 2

nd

cylinder

A32

A03

A33

Low fuel injector of 4

th

cylinder

A04

Power supply of EGR actuator

A34

A05

A35

Earthing of camshaft position sensor

A06

5V power supply of rail pressure sensor

A36

A07

5V power supply of absolute pressure sensor

A37

High coolant temperature signal

Outlet

Outlet

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Terminal

No.

Description

Terminal

No.

Description

A08

5V power supply of camshaft position sensor

A38

A09

A39

A10

A40

Earthing of rail pressure sensor

A11

A41

A12

A42

A13

Signal of crankshaft position sensor

A43

A14

Earthing of crankshaft position sensor

A44

A15

A45

A16

High fuel injector of 1

st

cylinder

A46

Low fuel injector of 3

rd

cylinder

A17

High fuel injector of 4

th

cylinder

A47

Low fuel injector of 1

st

cylinder

A18

A48

A19

Earthing of EGR actuator

A49

A20

A50

Low coolant temperature signal

A21

A51

A22

Air conditioner relay control

A52

Rail pressure sensor signal

A23

A53

Temperature signal of absolute pressure

sensor

A24

A54

Pressure signal of absolute pressure

sensor

A25

A55

A26

A56

Shielding wire of crankshaft position

sensor

A27

A57

Signal of camshaft position sensor

A28

Earthing of absolute pressure sensor

A58

A29

A59

A30

A60

Control of fuel metering unit

Interface K

K01

Positive pole of battery

K48

Vehicle speed sensor output

K02

Negative pole of battery

K49

K03

Positive pole of battery

K50

K04

Negative pole of battery

K51

Cruise control lamp

K05

Positive pole of battery

K52

Cruise control mode

K06

Negative pole of battery

K53

Cruise control mode

K07

K54 Anti-theft

cable

K08

K55 Clutch

switch

control

K09

K56

K10

K57

Preheating feedback signal

K11

K58

Grounding of accelerator pedal sensor 2

K12

Intake temperature signal of air flowmeter

K59

Pressure difference sensor signal

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Terminal

No.

Description

Terminal

No.

Description

K13

K60

Accelerator pedal sensor signal 2

K14

K61

K15

K62

K16

K63

Earthing signal of air flowmeter

K17

K64

K18

K65

K19

Vehicle speed signal input

K66

CAN communication

K20

Intake flow signal of air flowmeter

K67

Grounding of accelerator pedal sensor 1

K21

Exhaust brake switch control

K68

K22

Power supply 2 of accelerator pedal sensor

K69

Control signal of turbocharger actuator

K23

5V power supply of EGR

K70

Malfunction indicator lamp

K24

K71 OBD

indicator

lamp

K25

K72

K26

K73

K27

5V power supply of pressure difference sensor

K74

Cruise control mode

K28

Power supply 1 of accelerator pedal sensor

K75

K29

Exhaust brake relay control

K76

K30 Anti-theft

cable

K77 Water

level

signal

K31

Position signal of EGR

K78

Auxiliary brake switch

K32

K79

K33

K80

Earthing of pressure difference sensor

K34

K81

Accelerator pedal sensor signal 1

K35

K82

K36

K83

K37

Air conditioner switch signal

K84

K38 Main

brake

switch

K85

K39

Earthing of EGR position sensor

K86

K40

Cruise control mode

K87

CAN communication

K41

K88

K42

K89

K43

Engine speed signal output

K90

Preheating control signal

K44

Line K diagnosis

K91

Preheating indicator lamp

K45

K92

K46

Ignition switch power switch control

K93

K47

Main relay control

K94

4) Malfunction Mode

Unstable idling, poor acceleration, start failure, high idling, out-of-tolerance of emission, difficult start, failure of air
conditioner, control failure of fuel injector, engine flameout, etc.

Failure arising from the burnout of ECU internal parts due to electric overload of external devices; rusting of circuit

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board due to water ingress of ECU.

5) Troubleshooting

Connect the plug and use engine data diagnosis cable to read the engine malfunction records; disconnect the plug and
check whether the ECU connecting wire is intact. Mainly check whether ECU power supply and grounding circuit are
normal, whether the external sensors are working normally, whether the output signal are reliable, and whether the
circuit is intact.

Check whether the actuators are working normally and whether their circuits are intact. Finally replace the ECU for
test.

III. Actuators

1. Fuel injector

1) Overview

The fuel injectors are located on the engine cylinder head and are mainly functioned to provide accurate fuel injection
for the engine at the correct moment.

2) Working Principle

To realize effective fuel injection start point and accurate injection amount, the common rail system adopts the special
fuel injector with hydraulic servo system and electronic control unit (solenoid valve). At the start of fuel injection
process, the fuel injector needs to adopt a relatively high current to rapidly open the solenoid valve. Till the needle
valve of the fuel injector nozzle reaches the maximum travel and the fuel injector nozzle is fully opened, the control
current is reduced to a relatively low constant current. In
such case, the fuel injection amount depends on the open
moment and the pressure in the common rail. When the
solenoid valve is no longer working and is closed, the fuel
supply process is completed.

The fuel injection start moment and the fuel injection
amount are regulated by the electronically controlled fuel
injector. These fuel injectors substitute the fuel injector
assembly (injector nozzle and fuel injector body). Similar to
the fuel injector assembly of modern direct injection diesel
engine, the holders are used to install the fuel injector on the
cylinder head. In other words, it’s unnecessary to make any
large modification to the cylinder head to install the
common rail fuel injectors onto the modern direct injection
diesel engine.

Design structure

The fuel injector (figure) can be divided into several
functional blocks:

- Injector nozzle

- Hydraulic servo system

- Solenoid valve

As shown in the figure, the fuel enters into nozzle through
high pressure connecting pipe (4) and fuel inlet groove (10)
and enters into the valve control chamber (8) through fuel
inlet (7). The control chamber is connected with fuel return
pipe (1) via fuel drainage hole (6) and the fuel drainage hole

Fuel injector
a. Close of fuel injector (Still state) b. Open of fuel injector (Fuel
injection)
1. Fuel return pipe 2. Electric connector 3. Control unit
(electromagnetic field) 4. Rail fuel inlet (high pressure) 5. Ball
valve 6. Fuel drainage hole 7. Fuel inlet hole 8. Valve control
chamber 9. Valve control plunger 10. Fuel inlet groove to
injector nozzle 11. Injector nozzle needle valve

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is opened by solenoid valve. After the fuel drainage hole is closed, the hydraulic force applied onto the valve
controlled plunger (9) exceeds the pressure on the pressure shoulder of injector nozzle needle valve (11). Therefore,
the needle valve is pushed into the needle valve seat to block the high pressure passage to the combustion chamber.
When the solenoid valve of the fuel injector is actuated, the fuel drainage hole opens. In such case, the pressure in the
control chamber drops and thus the force applied onto the plunger reduces. Once the hydraulic pressure is less than the
force applied onto the pressure shoulder of the needle valve, the injector nozzle needle valve opens and the fuel injects
into the combustion chamber via the injection hole. The cause to indirectly control the injector nozzle needle valve by
hydraulic gain system is that the solenoid valve can’t directly generate the force required to rapidly open the needle
valve. The control amount required to open the injector nozzle needle valve is not included from the actual fuel
injection amount and is conveyed to the fuel return pipe through the fuel drainage hole of the control chamber.
Besides the control amount, the loss control fuel and the leak fuel at the injector nozzle needle valve and the valve
plunger chamber are conveyed to the fuel tank via the fuel return pipe and the fuel collection pipe connecting the
relief valve.
Depending on the working condition of the engine and the pressure generated by the high pressure fuel pump, the fuel
injector can be classified to 4 working conditions:

- Close of fuel injector (due to application of high pressure)

- Open of fuel injector (start of fuel injection)

- Full open of fuel injector

- Close of fuel injector (complete of fuel injection)

These working conditions are generated by means of the pressure distribution applied onto the fuel injector parts.
When the engine is stopped and there is no pressure in the common rail, the injector nozzle spring will close the fuel
injector.

Close of fuel injector (still state):

The solenoid valve is not actuated under still state and thus the fuel injector is closed (a). When the fuel drainage hole
is closed, the valve spring will press the ball vale of armature onto the fuel return orifice. The high pressure of
common rail is formed in the valve control chamber. Afterwards, a similar pressure is formed within the injector
nozzle chamber. The pressure applied onto the end face of control plunger by the rail pressure and the injector nozzle
spring force work together against the open force applied onto the conical pressure bearing face of needle valve by
fuel to maintain the needle valve at close state.

Open of fuel injector (start of fuel injection):

While the injector nozzle is at still state, the solenoid valve is actuated by the start current to ensure rapid open (b).
The force generated by the actuated solenoid valve overcomes the spring force so that the armature opens the fuel
drainage hole. Almost at the same time, the high start current drops to the low holding current required by the electric
magnet. This is possible as the air cap of the magnetic circuit becomes really small. When the ball valve of the fuel
drainage hole opens, the fuel flows from the valve control chamber to the empty chamber above and then returns to
the fuel tank via the fuel return pipe. The fuel drainage hole makes the pressure not completely balanced so that the
pressure in the valve control chamber drops. Therefore, the pressure in the valve control chamber is less than the
pressure of the fuel rail, which is still maintained in the fuel injector chamber, and the pressure drop in the valve
control chamber reduces the force applied onto the control plunger so that the injector nozzle needle valve opens and
the fuel injection starts.

The open speed of the injector nozzle needle valve depends on the flow difference between the fuel drainage hole and
the fuel inlet hole. The control plunger reaches its top dead center and then is held by one film of fuel, which is
formed by the fuel flow between the fuel drainage hole and the fuel inlet hole. In such case, the injector nozzle
completely opens and the fuel is injected into the combustion chamber at a pressure almost equaling to the fuel
pressure in the common rail. The pressure distribution in the injector nozzle is similar to that at the open stage.

Close of fuel injector (complete of fuel injection):

When the solenoid valve is no longer actuated, the valve spring pushes down the armature so that the ball of the valve

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closes the fuel drainage hole. The armature is of two-part design. Though the armature block is guided by the pressure
shoulder during the downward movement, it can bounce back following the return spring and thus will not apply
downward force onto the armature and the ball valve.
The close of fuel drainage hole enables the entry of fuel via fuel inlet hole into the control chamber for pressure
establishment. This pressure is equivalent to the rail pressure and applies additional force onto the end face of the
control plunger. The resultant force from this force and spring force overcomes the pressure in the injector nozzle
chamber to close the injector nozzle needle valve.
The close speed of the injector nozzle needle valve depends on the flow passing through the fuel inlet hole. Once the
injector nozzle needle valve hits its lower seat again, the fuel injection stops.

3) Measurement analysis

4) Matching of fuel injector

The matching of fuel injector must be performed in event of any
of the following conditions:

z Replacement of fuel injector.

z Replacement of ECU

z Confusion of installation serial number before and after the

maintenance.

While performing the matching, input the matching code on the
fuel injector (as shown in the figure) in order into the diagnosis
instrument for matching.

2. EGR valve control system

1) Overview

z The electronically controlled EGR valve controls the

open extent of the valve by means of the positive and
reverse rotation of the DC motor and performs the
close-loop control as per the feedback signal of the
position sensor.

z To guarantee the NOx emission of the engine, the ECU

measures and calculates the EGR percentage as per the
input parameters of the engine (such as speed and intake
pressure) and the calibrated MAPs), issues control
signal to the EGR valve, and performs the close-loop
control via the position sensor.

z The EGR valve is installed on the intake manifold. The constant temperature of the EGR valve inlet emission

Fuel injector 1 “high”

Fuel injector 1 "Low”

Fuel injector 4 “high”

Fuel injector 4 "Low”

Fuel injector 2 "Low”

Fuel injector 3 "Low”

Fuel injector 3 “high”

Fuel injector 2 “high”

Cylinder 1

Cylinder 4

Cylinder 3

Cylinder 2

EGR valve

Intake manifold

assembly

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can't exceed 260ºC, with the peak temperature no more than 300ºC.

2) Measurement analysis

3. Variable nozzle turbocharger (VNT) control

1) Overview

z HFC4DA1-2C adopts variable section turbocharger technology so that the turbocharger and the engine are well

matched under all working conditions to realize best engine performance.

z The blades of the VNT are connected to the control tie rod and the displacement of the control tie rod is

controlled by the vacuum pressure of the vacuum chamber on the VNT. Changing the vacuum pressure of the
vacuum chamber can change the position of VNT blades and control the flow area of the turbine. The vacuum
pressure of the vacuum chamber is controlled by VNT solenoid valve, of which one port is connected to the
vacuum chamber on the VNT, one port is connected to the vacuum pump, and another port is connected to the air.
This connector in the engine is additionally fitted with filter to prevent the ingress of contaminant (such as dust)
into the valve. The open extent of the VNT solenoid valve is regulated by the PWM wave issued by ECU and the
solenoid valve is installed on the crossbeam of the body water tank.

2) Measurement analysis

4. Fuel metering unit

1) Overview

The fuel metering unit is located on the high pressure fuel pump and is functioned to control the fuel amount from the
low pressure pump to the high pressure pump.

2) Working Principle

The fuel metering valve is installed at the high pressure fuel inlet of high pressure fuel pump and is functioned to
regulate the fuel supply amount and fuel pressure, of which the regulation requirement is subject to the control of
ECU. The control coil of the metering valve is closed when not electrified, which cuts off the fuel supply to the
plunger of high pressure fuel pump. The ECU changes the fuel inlet section area of metering unit by means of pulse
signal to increase or reduce the fuel supply amount.

3) Measurement analysis

Wiring terminals: 1 – Signal terminal; 2 – 12V voltage.

EGR power supply

EGR position signal

EGR signal grounding

EGR control signal terminal

EGR control grounding
terminal

EGR passage section

EGR actuator

Turbocharger actuator

Turbocharger control signal

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4) Malfunction Mode

Short-circuit or open-circuit of metering valve; damage of metering valve; contamination of metering valve.

5) Troubleshooting

Use Sunray special diagnosis instrument to check the trouble code and determine the malfunction position. Mainly
check the circuit of metering valve and determine whether there is short-circuit or open-circuit between circuit and the
grounding wire, whether there is short-circuit or open-circuit to power supply, and whether the circuit is consistent
with the given pin definition.

5. Preheating control unit

1) Overview

The preheating control unit is located in the engine compartment and is mainly functioned for the rapid start of engine
under cold state.

2) Working Principle

The preheating control unit is functioned to ensure effective cold start and shorten the warm-up time, which is closely
related to the exhaust emission. The preheating time is a function of coolant temperature. At the start of the engine or
during the actual running, the turn-on duration of the electric heating plug depends on one series of parameters,
including the fuel injection amount and engine speed. The control of the electric heating plug is realized by one power
relay (GCU).

The main part of the electric heating plug is the tubular heating unit. The heating unit is firmly and air-tightly installed
within the electric heating plug housing to guard against corrosion and thermal gas impact. The heating unit is one

Fuel metering unit signal

Fuel metering unit

CP1H and CP4.x metering unit

Fuel amount

Fuel supply to high

pressure pump

Full load fuel amount

Fuel amount characteristic

Idling fuel amount

Ampere