Technical Service Training
Diesel Injection and Engine
Management Systems
Common Rail Systems
CG 8258/S en 01/2008 TC304 3 060H
To the best of our knowledge, the illustrations, technical information, data and descriptions in this issue were correct at the time of going to print. The right to change prices, specifications, equipment and maintenance instructions at any time without notice is reserved as part of FORD policy of continuous development and improvement for the benefit of our customers.
No part of this publication may be reproduced, stored in a data processing system or transmitted in any form, electronic, mechanical, photocopy, recording, translation or by any other means without prior permission of Ford-Werke GmbH. No liability can be accepted for any inaccuracies in this publication, although every possible care has been taken to make it as complete and accurate as possible.
Copyright ©2008
Ford-Werke GmbH
More stringent exhaust and noise emission standards and calls for lower fuel consumption continue to place new demands on the fuel injection and engine management systems of diesel engines.
In order to satisfy these requirements, the injection system must inject the fuel at high pressure into the combustion chamber to provide good mixture preparation and, at the same time, meter the injected fuel quantity with the highest possible accuracy. The common rail system offers good potential for development, which is of particular significance both now and in the future. By separating the pressure generation process from the injection process, the optimum injection pressure is always available for the injection process, regardless of engine speed.
Modern engine management systems ensure that the fuel injection timing and injected fuel quantity are exactly calculated and delivered to the engine cylinders by the fuel injectors.
The following common rail systems are currently installed in Ford vehicles: – Bosch common rail system,
– Siemens common rail system, – Denso common rail system.
Another big step towards achieving cleanliness in diesel engines is the newly developed diesel particulate filter system. This system helps reduce micro-fine diesel particulates by up to 99%.
Completion of the eLearning program "Diesel Fuel Injection and Engine Management Systems" is a prerequisite for the study of this Student Information.
This Student Information is divided into lessons. At the end of each lesson there is a set of test questions that are designed to monitor the student's progress. The solutions to these test questions can be found at the end of the Student Information.
Please remember that our training literature has been prepared for FORD TRAINING PURPOSES only. Repairs and adjustments MUST always be carried out according to the instructions and specifications in the workshop literature. Please make full use of the training offered by Ford Technical Training Courses to gain extensive knowledge of both theory and practice.
PAGE
1
Preface...
Lesson 1 – General Information
6 Overview of the systems...
10 Introduction... 11 Injection characteristics... 13 Torque... 13 Emission Standard IV with or without DPF...
13 Cleanliness when working on the common rail system...
14 Test questions...
Lesson 2 – Fuel System
15 Overview... 20 Low-pressure system... 20 General... 21 Bosch common rail system...
21 Fuel filter...
25 Overview of the high-pressure system...
27 Fuel pump...
33 Fuel rail (common rail)...
33 High-pressure fuel lines...
33 Fuel injectors (general)...
34 Solenoid valve-controlled fuel injectors...
37 Piezo-controlled fuel injectors...
42 Siemens common rail system...
42 Fuel filter...
43 Overview of the high-pressure system...
44 Fuel pump...
47 Fuel rail and high-pressure fuel lines...
48 Fuel injectors...
53 Denso common rail system...
53 Fuel filter...
54 Overview of the high-pressure system...
55 Fuel pump...
58 Fuel rail and high-pressure fuel lines...
60 Fuel injectors...
62 Test questions...
Lesson 3 – Powertrain Control Module (PCM)
63 General... 63 Input signals... 63 Output signals... 64 Diagnosis... 65 PCM and peripherals... 65 Bosch common rail system...69 Siemens common rail system...
73 Denso common rail system...
75 Strategies...
75 Idle speed control...
75 Fuel metering calculations...
77 Smooth-running control (cylinder balancing)...
77 External intervention into the injected fuel quantity...
78 Controlling fuel injection...
79 Controlling the fuel pressure...
81 EGR system...
83 Boost pressure control...
86 EOBD...
86 General...
87 Fault logging and storing...
88 Test questions...
Lesson 4 – Sensors
89 Introduction... 89 CKP sensor... 91 CMP sensor... 92 MAP sensor... 93 IAT sensor... 93 MAPT sensor... 94 BARO sensor... 94 ECT sensor... 96 CHT sensor (Kent and Puma diesel engines only)...98 Combined IAT sensor and MAF sensor...
99 HO2S...
100 Turbocharger position sensor (certain versions only)...
101 Vehicle speed signal...
102 APP sensor...
103 Fuel temperature sensor...
104 Fuel pressure sensor...
105 Engine oil level sensor (2.4L/3.2L Duratorq-TDCi (Puma) diesel engine)...
107 Engine oil level sensor (2.2L Duratorq-TDCi (DW) diesel engine)...
109 Oil pressure switch...
109 Stoplamp switch/BPP switch...
110 CPP switch... 111 Test questions...
Lesson 5 – Actuators
112 Fuel metering valve...114 Fuel pressure regulator...
116 Fuel injectors (solenoid valve-controlled)...
118 Fuel injectors (piezo-controlled)...
119 EGR valve...
121 Wastegate control valve (vacuum-controlled systems)...
122 Intake manifold flap and intake manifold flap solenoid valve (vacuum-controlled systems)...
123 Intake manifold flap actuator motor (1.6L Duratorq-TDCi (DV) diesel engine, Emission Standard IV)...
125 Turbocharger variable vane electrical actuator...
128 Electric fuel pump (2.2L Duratorq-TDCi (DW) diesel engine only)...
129 Test questions...
Lesson 6 – Engine Emission Control
130 Introduction...
130 Pollutant emissions reduction...
130 DPF (general)...
131 Regeneration of the DPF (general)...
133 DPF with fuel additive system...
133 Component overview...
135 DPF...
136 Charge air cooler bypass...
138 Fuel additive system – general...
139 Components of the fuel additive system...
141 Component overview – system control...
143 PCM...
143 Fuel additive control unit...
144 Fuel additive pump unit...
145 Tank flap switch...
146 Exhaust gas temperature sensor(s)...
147 DPF differential pressure sensor ...
148 Intake manifold flap actuator motors (Bosch system only)...
148 Charge air cooler bypass flap actuator motor (Bosch system only)...
150 Intake manifold flap and charge air cooler bypass flap solenoid valves (Siemens system)...
151 Coated diesel particulate filter (DPF)...
151 Overview of the DPF... 151 Passive regeneration... 152 Active regeneration... 152 Notes on the oil change interval...
153 DPF regeneration indicator (2006.5 Transit only)...
153 Intake manifold flap...
154 Components of the engine emission control system...
155 Exhaust gas temperature sensor(s)...
155 DPF differential pressure sensor ...
156 Intake manifold flap position sensor (vacuum-controlled systems)...
157 Intake manifold flap unit...
158 Fuel vaporiser system...
158 General...
159 Fuel vaporiser system fuel pump...
160 Fuel vaporiser...
161 Test questions...
162
Answers to the test questions...
163
List of Abbreviations...
Overview of the systems
Bosch common rail system with "solenoid valve-controlled" fuel injectors
E51104
Bosch common rail system with "piezo-controlled" fuel injectors
E96077
Siemens common rail system
E53583
Denso common rail system
E69955
Assignment of the common rail systems to the engines
Denso Siemens Bosch Engine X 1.4L Duratorq-TDCi (DV) diesel X 1.6L Duratorq-TDCi (DV) diesel X* 1.8L Duratorq-TDCi (Kent) diesel
Denso Siemens Bosch Engine X 2.0L Duratorq-TDCi (DW) diesel X 2.2L Duratorq-TDCi (DW) diesel X* 2.2L Duratorq-TDCi (Puma) diesel X* 2.4L Duratorq-TDCi (Puma) diesel X 3.2L Duratorq-TDCi (Puma) diesel
* Older versions are equipped with the Delphi common rail system. The Delphi common rail system is not part of this Student Information.
Introduction
Increasingly higher demands are being placed on modern diesel engines. The focus today is not only on exhaust emissions but also on increasing environmental awareness and the demand for increasingly better economy and enhanced driving comfort.
This requires the use of complex injection systems, high injection pressures and accurate fuel metering by fully electronically-controlled systems.
The high injection pressures convert the fuel, via the injector nozzle, into tiny droplets, which, again due to the high pressure, can then be optimally distributed in the combustion chamber. This results in less unburned HC (Hydrocarbon), less CO (Carbon Monoxide) and fewer diesel exhaust particulates being produced in the subsequent combustion stage.
In addition, the optimised mixture formation reduces fuel consumption.
Diesel knock caused by the combustion process of an engine with direct injection is significantly reduced by means of additional pilot injection. NOX (Oxides Of Nitrogen) emissions can also be reduced by using this method.
In particular, the demands placed upon the injection system and its regulation are as follows for modern diesel engines:
• high injection pressures,
• shaping of injection timing characteristics, • multiple injections,
• values for injected fuel quantity, start of injection
and boost pressure adapted to every operating condition,
• load-independent idle speed control,
• closed-loop EGR (Exhaust Gas Recirculation), • low injection timing and injected fuel quantity
tolerances and high degree of precision over the entire service life,
• possibility of interaction with other systems such as
stability assist, PATS (Passive Anti-Theft System),
• comprehensive diagnostic facilities, • substitute strategies in the event of faults.
The common rail injection system has a large range of features to meet these demands.
In common rail injection systems, pressure generation is separate from the injection process. The injection pressure is generated independently of engine speed and injected fuel quantity.
The common rail injection system consists of a high-pressure pump and a fuel rail (fuel
accumulator/rail). This fuel rail offers constant pressure for distributing fuel to the electrically-controlled fuel injectors.
With this type of diesel injection or engine management, the driver has no direct influence on the injected fuel quantity. For example, there is no mechanical connection
between the accelerator pedal and the injection pump. The injected fuel quantity is determined by various parameters. These include:
• driver demand (accelerator pedal position), • operating condition,
• engine temperature,
• effects on exhaust emissions,
• prevention of engine and transmission damage, • faults in the system.
Using these parameters, the injected fuel quantity is calculated in the PCM (Powertrain Control Module) and fuel injection timing and injection pressure can be varied.
The fuel is metered fully electronically by the PCM. The fully electronic diesel engine management system features a comprehensive fail-safe concept (integrated in the PCM software). It detects any deviations and malfunctions and initiates corresponding actions depending on the resulting effects (e.g. limiting the power output by reducing the quantity of fuel).
Injection characteristics
As already mentioned at the beginning of the lesson, the exhaust emissions and fuel consumption of an engine are of great significance. These factors can only be minimised through precise operation of the injection system and comprehensive engine management strategies.
Consequently, the following requirements must be met by the common rail system:
• The injection timing must be exact. Even small
variations have a significant effect on fuel consumption, exhaust emissions and combustion noise.
• The fuel injection pressure is independently adapted
to all operating conditions.
• Injection must be reliably terminated. Calculation
of the injected fuel quantity and the injection timing is precisely adapted to the mechanical components of the injection system. Uncontrolled fuel dribble (e.g. caused by a defective fuel injector) results in increased exhaust emissions and increased fuel consumption.
Simple main injection
Needle lift of the fuel injector nozzle and pressure curve in a cylinder without pilot injection
E64973 1 2 3 4 5
Combustion pressure in the cylinder 1
Needle lift 2
TDC (Top Dead Center) 3
Needle lift with simple main injection 4
Crankshaft angle 5
In the case of diesel engines with a distributor-type
fuel injection pump (e.g. in the Transit 2000.5), fuel
injection takes place via simple main injection. The fuel is then injected mechanically into the combustion chamber by the injector nozzles in two seamlessly integrated stages (two-spring nozzle carrier principle).
In the pressure curve, the combustion pressure increases only slightly in the phase before TDC corresponding to compression, but increases very sharply at the start of combustion.
The sharp pressure rise intensifies the combustion noise.
Pilot injection
Needle lift of the fuel injector nozzle and pressure curve in a cylinder with pilot injection
E64974 1 2 3 4 5 6
Combustion pressure in the cylinder 1
Needle lift 2
TDC 3
Needle lift with pilot injection 4
Needle lift with main injection 5
Crankshaft angle 6
In the case of vehicles with a common rail injection
system, electrically-controlled pilot injection occurs
after a set time prior to the main injection event. Pilot injection means that a small amount of fuel is injected into the cylinder prior to the main injection. The small pilot-injection fuel quantity is ignited, heats up the upper part of the cylinder and thereby brings it into an optimum temperature range (preconditioning of the combustion chamber).
This means that the main injection mixture ignites more quickly and the rise in temperature and combustion pressure is less abrupt as a result.
Advantage:
• Continuous build-up of combustion pressure,
resulting in reduced combustion noise.
• Reduction of oxides of nitrogen in the exhaust gas.
Note: As pressure generation and injection are separate
in common rail systems, it is possible to considerably enhance the range for pilot injection. This has led to a significant improvement in the running smoothness of the engine.
With modern fuel injectors, it is also possible to work with multiple pilot injections. The greater the number of pilot injections, the lower the noise emissions.
Post-injection (vehicles with DPF (Diesel
Particulate Filter) system)
Needle lift of the injector nozzle with pilot and post-injection E51105 1 2 4 5 6 3 Needle lift 1 Pilot injection 2 Crankshaft angle 3 Main injection 4 Advanced post-injection 5 Retarded post-injection 6
For vehicles with a DPF (Diesel Particulate Filter) system, two post-injections are employed during the regeneration process, in addition to the pilot and main injections, depending on the requirements.
Advanced post-injection is initiated in certain
load/speed ranges immediately after main injection. Fuel is then injected during the on-going combustion. The main purpose of this advanced post-injection is to raise the exhaust gas temperature during the regeneration process of the DPF. In addition, some of the diesel particulates produced during regeneration are after-burned.
Retarded post-injection only occurs shortly before
BDC (Bottom Dead Center) and also serves to raise the exhaust gas temperature.
In contrast to advanced post-injection, during retarded post-injection the fuel is not burned, but vaporises due to the residual heat in the exhaust gas. This exhaust/fuel mixture is delivered to the exhaust system by the exhaust stroke.
In the oxidation catalytic converter, the fuel vapour reacts with the residual oxygen (above a certain temperature) and burns. This provides sustained heating of the oxidation catalytic converter, which supports the regeneration of the DPF.
Torque
In general, diesel engines generate a high torque across a wide engine speed range. This is achieved through uniformly good cylinder charging (working without a throttle plate) and high combustion pressure.
Overtorque function
On some vehicle versions, an overtorque function (also called an overboost function) is used. This makes it possible to briefly exceed the maximum specified torque during rapid acceleration (by about 15 to 35 Nm depending on the calibration).
The short-term torque increase is an advantage when overtaking, for example.
The vehicle acceleration is calculated based on the vehicle speed signal and the CKP (Crankshaft Position) sensor. During acceleration, the PCM activates the overtorque function in an engine speed range between 1,700 and 3,500 rpm.
Emission Standard IV with or without
DPF
At the time of going to press, Emission Standard IV applies in Europe.
In the diesel sector, Emission Standard IV is achieved using two different methods.
One method consists of reducing exhaust emissions by
means of internal engine measures to the extent that the prescribed limits are met.
Measures for the reduction of exhaust emissions inside the engine include, for example:
• further optimised exhaust gas recirculation by means
of an electrically-controlled EGR system with intake air restriction,
• optimisation of the combustion chamber design and
the injection characteristics.
In addition to the internal engine measures, the second
method employs a DPF system.
The use of the DPF reduces diesel particulate emissions by up to 99%. This reduction far exceeds the
requirements for the European emission limits of Emission Standard IV.
It can therefore be deduced that the use of the DPF will be of great importance with regard to future emission standards, but is not absolutely necessary for meeting Emission Standard IV.
Cleanliness when working on the
common rail system
NOTE: Because the components of the high-pressure
fuel system are high-precision machined parts, it is essential that scrupulous cleanliness is observed when carrying out any work on the system.
In this regard, refer to the instructions in the current Service Literature.
Tick the correct answer or fill in the gaps.
1. What is the advantage of the common rail system?
a. The high injection pressures reduce combustion temperatures; exhaust gas recirculation is not required. b. Pressure generation and injection are separated.
c. The injection pressure is generated as a function of engine speed.
d. Combustion noise is substantially reduced as a result of indirect injection.
2. What is the effect of pilot injection?
a. Pilot injection results in an abrupt build-up of combustion pressure and therefore reduced combustion noise. b. Pilot injection results in an abrupt build-up of combustion pressure and therefore increased combustion
noise.
c. Pilot injection results in a gradual increase in combustion pressure. d. Pilot injection only results in a reduction of fuel consumption.
3. Where are post-injections utilised?
a. In vehicles with an electric EGR system. b. In vehicles with an NOX catalytic converter.
c. In vehicles without a diesel particulate filter system. d. In vehicles with a diesel particulate filter system.
4. The overtorque function
a. prevents abrupt deceleration when the accelerator pedal is suddenly released at high vehicle speeds. b. makes it possible to briefly exceed the maximum specified torque when starting the vehicle on a gradient. c. makes it possible to briefly exceed the maximum specified torque during rapid acceleration.
d. is activated in response to certain malfunctions in the engine management system.
Lesson 1 – General Information
Test questions
Overview
Bosch common rail system with "solenoid valve-controlled" fuel injectors
E51106 7 6 G A B C D E F 5 1 2 3 4 8 Fuel line A
Run-off line for excess delivered fuel B
High-pressure line C
Fuel injection line D
Fuel return from the fuel pump E
Leak-off pipe F
Fuel return to the fuel tank G
Fuel pump 1
Fuel rail (common rail) 2
Fuel injector 3
Fuel temperature sensor 4
Fuel return collector pipe 5
Fuel filter
6 7 Fuel tank
Fuel pump and sender unit 8
Bosch common rail system with "piezo-controlled" fuel injectors
E96088 1 2 4 5 8 6 B A F E 7 C D 3
Fuel return from the fuel pump A
High-pressure line B
Fuel injection line C
Leak-off pipe D
Fuel return to the fuel tank E Fuel line F Fuel pump 1 Fuel rail 2 Fuel injector 3
Back pressure valve 4
Return gateway 5
Fuel tank 6
Fuel pump and sender unit 7
Fuel filter 8
Siemens common rail system
E53588 7 8 6 4 F A B C D E 1 2 3 5 Fuel line A High-pressure line B
Fuel injection line C
Fuel return from the fuel pump D
Leak-off pipe E
Fuel return to the fuel tank F
Fuel pump 1
Fuel rail (common rail) 2
Fuel injector 3
Fuel return collector pipe 4
Fuel temperature sensor 5 Fuel filter 6 Fuel tank 7
Fuel pump and sender unit 8
Denso common rail system
E69808 1 2 3 4 5 8 6 B A F E 7 C D
Fuel return from the fuel pump A
High-pressure line B
Fuel injection line C
Leak-off pipe D
Fuel return to the fuel tank E
Fuel line F
Fuel pump 1
Fuel rail (common rail) 2
Fuel injector 3
Pressure relief valve 4
T-piece 5
Fuel tank 6
Fuel pump and sender unit 7
Fuel filter 8
General
Function
Fuel is drawn from the fuel tank through the fuel filter by the transfer pump which is integrated in the fuel pump.
The fuel pump compresses the fuel and forces it into the fuel rail.
The fuel pressure required for any given situation is available for the fuel injectors for each injection process. Leak-off fuel from the fuel injectors and/or returning fuel from the fuel pump is fed back into the fuel tank.
Possible causes of faults in fuel lines and the fuel
tank
Fuel lines may be blocked due to foreign bodies or bending.
In addition, blocked parts and lines of the low-pressure system can cause air to get into the low-pressure system on account of the increased vacuum in the system. Air can also enter the low-pressure system through loose or leaking line connections.
Faulty valves or lines in the tank ventilation system can impair the flow of fuel through the low-pressure system.
Effects of faults (low-pressure system contains
air or is blocked)
Poor engine starting when warm or cold. Irregular idling.
Engine will not start.
Engine starts, but cuts out again immediately afterwards. Engine has insufficient power.
Note: At a certain residual fuel amount, the PCM causes
the engine to judder. The intention is to draw the driver's attention to the fact that the vehicle must urgently be refuelled.
Note for vehicles with EOBD: If the PCM causes the
engine to judder because the fuel tank is empty, the EOBD (European On-Board Diagnostics) are deactivated during this phase. This prevents apparent faults from being displayed.
Lesson 2 – Fuel System
Low-pressure system
Fuel filter
System with solenoid valve-controlled fuel
injectors
E43249 1 4 3 2Fuel line to the fuel pump 1
Water drain screw 2
Electric fuel preheater 3
Fuel line connection with fuel tank 4
The fuel filter clipped onto the transaxle end of the cylinder head is equipped with an electric fuel heater. There is a water drain screw in the top section of the filter housing for draining the filter.
The fuel filter must be drained of water regularly in accordance with the service intervals.
E51107 1 2 5 6 1 15 30 3 2 4 3 2 1 5 7 6
Battery junction box 1
Fuel preheater relay 2 Fuse (10A) 3 Fuse (15A) 4 Ground 5
Electric fuel preheater in the fuel filter 6
Ground 7
The electric bimetallically-controlled fuel preheater works independently of the PCM.
It is actuated via a fuel preheater relay when the ignition is switched on (ignition ON). However, the activation of the heating element is dependent on the current temperature.
Below a fuel temperature of 0 to –4 °C, the circuit is closed by the bimetal and the heating element thus energised.
The bimetal opens the circuit at a fuel temperature from 1 to 5 °C and ends the heating phase.
Bosch common rail system
Lesson 2 – Fuel System
System with piezo-controlled fuel injectors
1 2 3 4 5 6 7 1 2 3 4 5 6 7 E97401Fuel return (to the fuel tank) 1
Fuel return line (from the fuel pump) 2
Fuel temperature sensor 3
Fuel line (to the fuel pump) 4
Fuel filter water drain screw 5
Water drain line 6
Fuel line (from the fuel tank) 7
The fuel filter is made of plastic. It is installed on the front side of the engine on the intake side. A security shield protects the fuel filter from damage in the event of a frontal impact.
Located on the fuel filter housing is a water drain screw. The fuel filter must be drained via this screw in accordance with the service intervals.
Note:
• Before draining the fuel filter, make sure that the
surrounding components do not come into contact with the fuel that is drained.
There is a thermo valve integrated in the fuel filter for
preheating the fuel.
Lesson 2 – Fuel System
Bosch common rail system
How fuel preheating works 1 2 3 4 5 6 7 A B 1 2 3 4 5 6 7 A B E96134
Fuel return temperature < 10 °C A
Fuel return temperature > 20 °C B
Fuel return line (to the fuel tank) 1
Fuel return outlet 2
Bypass (to the fuel filter) 3
Upper part of the fuel filter 4
Fuel return line (from the fuel pump) 5
Thermostat open 6
Thermostat closed 7
The fuel filter is equipped with a mechanical fuel preheater.
There is a spring-loaded thermo valve integrated in the fuel return in the upper part of the fuel filter. The thermo valve determines the quantity of fuel that is returned to the fuel tank or flows directly back into the fuel filter.
Fuel return temperature < 10 °C:
• The thermo valve is in compressed state.
• The bypass to the fuel filter is wide open in this state.
The cross section of the fuel return outlet is slightly open.
• The majority of the returning fuel flows through the
wide open bypass into the fuel filter. Only a small part of the returning fuel can flow back to the fuel tank via the slightly open cross section of the fuel return outlet.
Bosch common rail system
Lesson 2 – Fuel System
Fuel return temperature > 20 °C:
• The thermo valve expands against the spring force. • The bypass to the fuel filter is only slightly open in
this state. The cross section of the fuel return outlet is now wide open.
• The majority of the returning fuel flows through the
wide open fuel return outlet. Only a small part of the returning fuel can flow through the slightly open bypass to the fuel filter.
Percentage of fuel to the fuel filter Percentage of fuel to the fuel tank
Fuel return temperature
90 - 95 % 5 - 10 % < 10 °C 0 - 5 % 95 - 100 % > 20 °C
Possible causes of faults
Fuel filters may be blocked by dirt. Air may also enter the low-pressure system as a result of leaks in the fuel filter.
Effects of faults
Poor starting when the engine is warm or cold.
Irregular idling. Engine will not start.
Engine starts, but cuts out again immediately afterwards. Engine has insufficient power.
Lesson 2 – Fuel System
Bosch common rail system
Overview of the high-pressure system
System with "solenoid valve-controlled" fuel injectors
E51108 3 4 5 6 7 8 9 1 2 Fuel injector 1
Fuel injection line 2
Leak-off pipe 3
Fuel metering valve 4 Transfer pump 5 High-pressure line 6 Fuel pump 7
Fuel rail (common rail) 8
Fuel pressure sensor 9
Bosch common rail system
Lesson 2 – Fuel System
System with "piezo-controlled" fuel injectors 2 3 4 5 6 7 8 9 10 1 11 2 3 4 5 6 7 8 9 10 1 11 E97421 Fuel injector 1
Fuel pressure sensor 2
Fuel rail (common rail) 3
Fuel injection line 4
High-pressure line 5
Overpressure leakage line 6
Fuel pressure control valve 7 Fuel return 8 Fuel pump 9 Fuel line 10
Set of leak-off pipes with back pressure valve * 11
* There is a back pressure valve in the set of leak-off
pipes. This valve maintains a back pressure of approx. 10 bar in the leak-off pipe while the engine is running. The back pressure valve cannot be renewed separately during servicing.
Lesson 2 – Fuel System
Bosch common rail system
Fuel pump
Overview
CP3.2 fuel pump E51109 1 2 3 4 5 6 Transfer pump 1Fuel metering valve 2 Pump plunger 3 Eccentric 4 Halfshaft 5 Pump housing 6
Bosch common rail system
Lesson 2 – Fuel System
CP1H fuel pump E70770 2 3 4 5 1
Fuel metering valve 1
Fuel return connection 2
Fuel line connection 3
Transfer pump 4
High-pressure connection (to the fuel rail) 5
Two different types of fuel pump are used in the Bosch common rail system:
• CP3.2 fuel pump and • CP1H fuel pump.
With the launch of the Focus C-MAX 2003.75
(06/2003-), initially only the CP3.2 was installed. Over time, the CP3.2 was increasingly replaced by the CP1H and this pump was installed from the outset for new launches.
The following table shows the introduction dates for the CP1H based on the vehicle.
Introduction of CP1H Vehicle October 2004 Fiesta 2002.25 (11/2001-) February 2005 Focus C-MAX 2003.75 (06/2003-)/Focus 2004.75 (07/2004-) with 67 kW (90 PS) May 2005 Focus C-MAX 2003.75 (06/2003-)/Focus 2004.75 (07/2004-) with 82 kW (110 PS)
With the start of produc-tion
Mondeo 2007.5/S-MAX/ Galaxy 2006.5
The function of the CP1H fuel pump is essentially the same as that of the CP3.2.
Lesson 2 – Fuel System
Bosch common rail system
Flow of fuel through the fuel pump
E51111 5 4 2 6 E D C 3 B F A 1 7 8 9 GTo the fuel injectors A
High fuel pressure B
Flow of fuel through the fuel pump C
Return flow to the transfer pump D
Fuel line E
Fuel injector leak-off F Fuel return G Fuel rail 1 High-pressure part 2 Pressure restrictor 3
Fuel metering valve 4
Overflow throttle valve 5 Fuel pump 6 Transfer pump 7 Fuel filter 8 Fuel tank 9
Bosch common rail system
Lesson 2 – Fuel System
Transfer pump
E51110 2 3 1 Intake side 1 Drive gear 2 Delivery side 3The transfer pump is designed as a gear pump and delivers the required fuel to the fuel pump.
Essential components are two counter-rotating, meshed gears that transport the fuel in the tooth gaps from the intake side to the delivery side.
The contact line of the gears forms a seal between the intake side and the delivery side and prevents the fuel from flowing back.
The delivery quantity is approximately proportional to the engine speed. For this reason, fuel quantity control is required.
There is an overflow throttle valve incorporated in the fuel pump for fuel quantity control purposes.
Overflow throttle valve
E51112 6 6 6 3 3 3 4 4 8 7 7 7 9 5 C B A 5 5 1 2 1 2 1 2 4 8
Low engine speeds A
Increasing engine speeds B
High engine speeds C
Transfer pump pressure 1 Time 2 Compression spring 3 Restrictor 4
To the high-pressure chambers 5
Lesson 2 – Fuel System
Bosch common rail system
Control piston 6
Fuel pump lubrication/cooling/ventilation 7
Fuel pump cooling bypass 8
Return bypass to the transfer pump 9
High-pressure generation (up to 1,800 bar) means high thermal load on the individual components of the fuel pump. The mechanical components of the fuel pump must also be sufficiently lubricated to ensure durability. The overflow throttle valve is designed to ensure optimum lubrication or cooling for all operating conditions.
At low engine speeds (low transfer pump pressure), the control piston is moved only slightly out of its seat. The lubrication/cooling requirement is correspondingly low. A small amount of fuel is released to lubricate/cool the pump via the restrictor at the end of the control piston.
NOTE: The fuel pump features automatic venting. Any
air present in the fuel pump is vented through the restrictor.
With increasing engine speed (increasing transfer pump pressure), the control piston is moved further against the compression spring.
Increasing engine speeds require increased cooling of the fuel pump. Above a certain pressure, the fuel pump cooling bypass is opened and the flow rate through the fuel pump is increased.
At high engine speeds (high transfer pump pressure), the control piston is moved further against the
compression spring. The fuel pump cooling bypass is now fully open (maximum cooling).
Excess fuel is transferred to the intake side of the transfer pump via the return bypass.
In this way, the internal pump pressure is limited to a maximum of 6 bar.
High-pressure generation
E51113 9 8 7 3 2 1 4 6 5Bosch common rail system
Lesson 2 – Fuel System
High pressure to the fuel rail 1 Exhaust valve 2 Spring 3 Fuel line 4 Halfshaft 5 Eccentric cam 6 High-pressure chamber 7 Pump plunger 8 Intake valve 9
The fuel pump is driven via the halfshaft. An eccentric element is fixed to the halfshaft and moves the three plungers up and down according to the shape of the cams on the eccentric element.
Fuel pressure from the transfer pump is applied to the intake valve. If the transfer pressure exceeds the internal pressure of the high-pressure chamber (pump plunger in TDC position), the intake valve opens.
Fuel is now forced into the high-pressure chamber, which moves the pump plunger downwards (intake stroke).
If the BDC position of the pump plunger is exceeded, the intake valve closes due to the increasing pressure in the high-pressure chamber. The fuel in the high-pressure chamber can no longer escape.
As soon as the pressure in the high-pressure chamber exceeds the pressure in the fuel rail, the outlet valve opens and the fuel is forced into the fuel rail via the high-pressure connection (delivery stroke).
The pump plunger delivers fuel until TDC is reached. The pressure then drops so that the outlet valve closes. As the pressure on the remaining fuel is reduced, the pump plunger moves downward.
If the pressure in the high-pressure chamber falls below the transfer pressure, the intake valve reopens and the process starts again.
Zero delivery valve
E51114
2 3
1
4
From the high-pressure chamber annular channel 1
Zero delivery valve 2
Calibrated bore (ø = 0.4 mm) 3
To the transfer pump 4
The zero delivery valve is located between the annular channel that is connected to the intake valves of the high-pressure chambers and the fuel metering valve. Even in the fully closed state, the fuel metering valve (see "Lesson 3 – Engine management system") is not
completely sealed. In other words, a small amount of leakage still gets into the annular channel to the
high-pressure chambers due to the transfer pump pressure. As a result, the intake valves are opened and an undesirable pressure increase may occur in the high-pressure system.
To prevent this, the zero delivery valve features a calibrated bore. In this way, excess fuel is fed back to the intake side of the transfer pump.
Lesson 2 – Fuel System
Bosch common rail system
Fuel rail (common rail)
Structure and purpose
E43248
1
Fuel pressure sensor 1
The fuel rail is made of forged steel.
The fuel rail performs the following functions:
• stores fuel under high pressure and • minimises pressure fluctuations.
Pressure fluctuations are induced in the high-pressure fuel system due to the operating movements in the high-pressure chambers of the fuel pump and the opening and closing of the solenoid valves on the fuel injectors.
Consequently, the fuel rail is designed in such a way that, on the one hand, it possesses sufficient volume to
minimise pressure fluctuations, but, on the other hand,
the volume in the fuel rail is sufficiently low to build up the fuel pressure required for a quick start in the shortest possible time.
Function
The fuel supplied by the fuel pump passes through a high-pressure line to the high-pressure accumulator. The fuel is then sent to the individual fuel injectors via the four fuel injection lines which are all the same length.
When fuel is taken from the fuel rail for an injection process, the pressure in the fuel rail remains almost constant.
Fuel pressure sensor
There is a fuel pressure sensor located on the fuel rail so that the engine management system can precisely determine the injected fuel quantity as a function of the current fuel pressure in the fuel rail (see "Lesson 4 – Sensors").
High-pressure fuel lines
E43246
NOTE: The bending radii are exactly matched to the
system and must not be changed.
NOTE: After disconnecting one or more high-pressure
fuel lines, these must always be renewed. The reason for this is that leaks can occur when retightening due to distortion of the connections of the old lines.
The high-pressure fuel lines connect the fuel pump to the fuel rail and the fuel rail to the individual fuel injectors.
Fuel injectors (general)
Depending on the engine type, different fuel injectors are used:
• solenoid valve-controlled fuel injectors or • piezo-controlled fuel injectors.
Solenoid valve-controlled fuel injectors are installed
in the 1.6L Duratorq-TDCi (DV) diesel engine.
Piezo-controlled fuel injectors are installed in the 2.2L
Duratorq-TDCi (DW) diesel engine.
Start of injection and injected fuel quantity are controlled via the fuel injectors.
Bosch common rail system
Lesson 2 – Fuel System
The injection timing is calculated using the angle/time system in the PCM. The main input variables for this are the signals from the CKP and the CMP (Camshaft Position) sensors.
Solenoid valve-controlled fuel injectors
E43245 3 4 2 5 1 7 6
Leak-off pipe connection 1 Retainer 2 Plastic ring 3 Seal 4
Combustion chamber seal 5
High-pressure fuel line connection 6
Solenoid valve connector 7
NOTE: The combustion chamber seals must not be
reused. The exact procedure for the correct installation of the seals and the plastic rings can be found in the current Service Literature.
The fuel injectors are divided into different function blocks:
• injector nozzle,
• hydraulic servo system, • solenoid valve.
Lesson 2 – Fuel System
Bosch common rail system
Function
E51115 B A 11 12 13 9 8 7 6 10 11 1 2 9 8 7 6 5 4 3 10Fuel injector closed A
Fuel injector open B
Solenoid valve coil 1 Feed channel 2 Valve ball 3 Feed restrictor 4
Feed channel to the nozzle prechamber 5
Nozzle needle 6
Nozzle prechamber 7
Nozzle needle spring 8
Valve control piston 9
Valve control chamber 10
Outlet restrictor 11
Bosch common rail system
Lesson 2 – Fuel System
Fuel return
12 13 Solenoid valve connector
The fuel is fed from the high-pressure connection via a feed channel into the nozzle prechamber and via the feed restrictor into the valve control chamber.
The valve control chamber is connected to the fuel return via the outlet restrictor, which can be opened by means of a solenoid valve.
Fuel injector closed
In its closed state (solenoid valve de-energised), the outlet restrictor is closed by the valve ball so that no fuel can escape from the valve control chamber. In this state, the pressures in the nozzle prechamber and in the valve control chamber are the same (pressure balance).
There is, however, also a spring force acting on the nozzle needle spring so that the nozzle needle remains closed (hydraulic pressure and spring force of the nozzle needle spring). No fuel can enter the combustion chamber.
Fuel injector opens
The outlet restrictor is opened via actuation of the solenoid valve. This lowers the pressure in the valve control chamber, as well as the hydraulic force on the valve control piston.
As soon as the hydraulic force in the valve control chamber falls below that of the nozzle prechamber and the nozzle needle spring, the nozzle needle opens. Fuel is now injected into the combustion chamber via the spray holes.
Fuel injector closes
After a period determined by the PCM, the power supply to the solenoid valve is interrupted.
This results in the outlet restrictor being closed again. By closing the outlet restrictor, pressure from the fuel rail builds up in the valve control chamber via the feed restrictor.
This increased pressure exerts an increased force on the valve control piston. This force and the spring force of the nozzle needle spring now exceed the force in the nozzle prechamber and the nozzle needle closes.
Note: The closing speed of the nozzle needle is
determined by the flow rate at the feed restrictor. Injection terminates when the nozzle needle reaches its bottom stop.
Indirect actuation
Indirect actuation of the nozzle needle via a hydraulic booster system is used because the forces required for rapid opening of the nozzle needle cannot be generated directly with the solenoid valve.
The "control quantity" therefore required in addition to the injected fuel quantity enters the fuel return via the restrictors in the control chamber.
Leak-off quantities
In addition to the control quantity, there are leak-off quantities at the nozzle needle and valve control piston guides.
These leak-off quantities are also discharged into the fuel return.
Service instructions (fuel injector correction
factor)
E51116 01 15440 136 080F DDFO 7606 80 38415 015 1724 2809 1 2 Fuel injector 1 Correction factor 2Inside the hydraulic servo system there are various restrictors with extremely small diameters which have specific manufacturing tolerances.
These manufacturing tolerances are given as part of a correction factor which is located on the outside of the fuel injector.
Lesson 2 – Fuel System
Bosch common rail system
To ensure optimum fuel metering, the PCM must be informed when a fuel injector is changed.
Furthermore, after new PCM software has been loaded via the IDS (Integrated Diagnostic System), the fuel injectors must also be configured with this software. This is done by inputting the 8-digit correction factor (divided into two blocks of four on the fuel injector) into the PCM with the help of the IDS and taking into account the corresponding cylinder.
Note: If the correction factors are not entered properly
with the IDS, the following faults can occur:
• increased black smoke formation, • irregular idling,
• increased combustion noise, • engine will not start.
Effects of faulty fuel injector(s) (mechanical
faults)
Increased black smoke production. Fuel injector leaks.
Increased combustion noise as a result of coked nozzle needles.
Irregular idling.
Piezo-controlled fuel injectors
1 2 3 4 6 5 1 2 3 4 6 5 E96132
Fuel injector retaining bolt 1
Retaining clip centring pin 2 Seal 3 Centring ring 4 Fuel injector 5 Retaining clip 6
Bosch common rail system
Lesson 2 – Fuel System
The fuel injectors are mounted on the cylinder head and protrude into the centre of the individual combustion chambers.
The fuel injectors are opened and closed using a piezo element. The piezo element is located inside the fuel injector.
The piezo-controlled fuel injectors switch around four
times faster than solenoid valve-controlled fuel
injectors.
The results in the following advantages:
• Multiple injections with flexible injection timing and
intervals between the individual injections.
• Realisation of very small injected fuel quantities for
the pilot injection(s).
• Low noise emissions (up to 3 dB). • Improved fuel economy (up to 3%). • Lower exhaust emissions (up to 20%). • Increased engine power output (up to 7%). • Improved running smoothness.
Function
Structure of the piezo-controlled fuel injector
E97388
1
2
3
4
5
6
a
b
Fuel return a High-pressure connection b Piezo element 1 Hydraulic coupler 2 Control valve 3Nozzle module with nozzle needle 4
Spray holes 5
Electrical connector 6
In the case of the piezo-controlled fuel injector, the nozzle needle is indirectly controlled via a control valve. 'Indirectly' means that the nozzle needle is opened and closed via a hydraulic circuit.
The hydraulic circuit comprises a low-pressure and a high-pressure part. The control valve provides the interface between the high-pressure and the low-pressure parts.
The required injected fuel quantity is controlled via the opening times of the control valve.
Lesson 2 – Fuel System
Bosch common rail system
Function of the control valve a b c A B C 1 2 4 3 5 6 a b c A B C 1 2 4 3 5 6 E97392 Initial position A
Nozzle needle opens B
Nozzle needle closes C Control valve 1 Outlet restrictor 2 Control chamber 3 Feed restrictor 4 Nozzle needle 5 Bypass 6
Fuel rail pressure a
Leak-off pressure b
Control chamber pressure c
Initial position
• If the piezo element is not activated by the PCM,
then the control valve is in the initial position. This means that the high-pressure part is closed off from the low-pressure part.
• The fuel rail pressure plus the spring force is acting
upon the nozzle needle. The fuel injector nozzle is closed (no injection).
Nozzle needle opens
• When the piezo element is activated, the control
valve opens and closes the bypass.
• The pressure in the control chamber can then escape
into the fuel return.
• The pressure in the control chamber is reduced via
the flow rate ratio of the outlet and feed restrictors.
• The fuel rail pressure on the nozzle needle is now
greater than the pressure in the control chamber and the spring force. The nozzle needle is lifted and injection begins.
Bosch common rail system
Lesson 2 – Fuel System
Nozzle needle closes
• When the piezo element is discharged by the PCM,
the control valve opens the bypass once more.
• The control chamber is then filled again via the feed
and outlet restrictors. The control chamber pressure increases again rapidly via the bypass.
• As soon as the control chamber pressure plus the
spring force are once more greater than the fuel rail pressure on the nozzle needle, the nozzle needle closes and injection ends.
Hydraulic coupler 1 3 2 4 6 5 1 3 2 4 6 5 E97396 Piezo element 1
Back pressure valve 2
Hydraulic coupler back pressure 3
Hydraulic coupler 4
Control valve piston 5
Piezo element piston 6
The hydraulic coupler fulfils the following functions:
• Transmission and amplification of the piezo stroke. • Compensation of any play.
• Termination of injection in the event of electrical
disconnection of the fuel injector (e.g. if a cable breaks during the injection process).
The hydraulic coupler is comparable to a hydraulic lash adjuster in terms of its function.
The fuel around the hydraulic coupler has a back pressure of approx. 10 bar. The back pressure valve is located in the leak-off pipe.
Piezo element not actuated:
• In this state, the pressure in the hydraulic coupler is
in balance with its surroundings (around 10 bar).
Piezo element actuated:
• The piezo element piston moves downwards. As a
result, the pressure in the hydraulic coupler rises. A small amount of leakage flows from the hydraulic coupler into the low-pressure circuit of the fuel injector via the piston guide clearances.
• The pressure increase in the hydraulic coupler causes
downward movement of the control valve piston via the hydraulic cushion and injection starts.
Once the injection process is finished, the deficit in the coupler must be refilled. This is done in reverse via the guide clearances of the piston.
The back pressure of around 10 bar is extremely
important for the correct operation of the fuel injectors.
Service instructions (fuel injector correction
factor)
E96133
Inside the hydraulic servo system there are calibrated bores with extremely small diameters. These bores have specific manufacturing tolerances. Tolerances also arise when the mechanical, hydraulic and electrical
components are combined.
At the factory, each fuel injector is tested and then sorted into a specific category. The fuel injector is assigned a correction factor according to the category.
The 10-digit correction factor is engraved on the head of the fuel injector (arrow).
Lesson 2 – Fuel System
Bosch common rail system
To ensure precise fuel metering, the PCM must be informed when an injector is changed.
The correction factor is entered with the help of the IDS. When entering the number, make sure that the fuel injector is assigned to the correct cylinder.
Effects of faults
Fuel injector(s) (mechanical faults):
• increased black smoke production, • fuel injector leaks,
• increased combustion noise as a result of coked
nozzle needles.
Bosch common rail system
Lesson 2 – Fuel System
Fuel filter
Function
Fuel filter of the 1.4L Duratorq-TDCi (DV) diesel engine
E53589 1 2 3 5 4
Fuel line connection (from the fuel tank) 1
Fuel line connection (to the fuel pump) 2
Fuel filter with water separator 3
Water drain screw 4
Electric fuel preheater 5
Different fuel filters are used for the Siemens common rail system depending on the type of engine. Their operating principles and service-relevant characteristics, however, are very similar.
Both fuel filters are equipped with a water separator which must be drained regularly in accordance with the specified service intervals.
Both fuel filters also feature a fuel preheater which is activated at low temperatures.
Fuel filter of the 2.0L Duratorq-TDCi (DW) diesel engine
E43236
1 2
3
4
Fuel line connection (from the fuel tank) 1
Fuel feed connection (to the fuel pump) 2
Electric fuel preheater 3
Water drain screw 4
The fuel preheater is bimetallically-controlled and functions independently of the PCM.
The bimetallically-controlled fuel preheater is activated when the ignition is on (ignition key in position II) regardless of whether the engine is running or not. The bimetal closes the circuit as a function of the ambient temperature and the heating element in the fuel preheater is activated.
• For the 1.4L Duratorq-TDCi, the on/off temperature
for the heating element is approximately 5 °C.
• For the 2.0L Duratorq-TDCi (DW) diesel engine,
the heating element is switched on at –2 °C ± 2 °C and switched off at +3 °C ± 2 °C.
Possible causes of faults
Fuel filters may be blocked by dirt. Air may also enter the low-pressure system as a result of leaks in the fuel filter.
Note: A certain quantity of air is drawn out of the fuel
tank together with the fuel when the transfer pump draws fuel into the fuel pump. The air bubbles are very small, however, and cannot initially be seen with the naked eye.
The small air bubbles are separated out in the fuel filter and clump together to form larger bubbles. These air bubbles occasionally emerge from the filter material
Lesson 2 – Fuel System
Siemens common rail system
and are drawn into the fuel pump. They can be seen through a transparent hose. This form of separation is entirely normal.
The visual inspection for air bubbles in the transparent hose is therefore not counted as a fault diagnosis.
Effects of faults
Poor starting when the engine is warm or cold. Irregular idling.
Engine will not start.
Engine starts, but cuts out again immediately afterwards. Engine has insufficient power.
Overview of the high-pressure system
Illustration shows the high-pressure system of the 2.0L Duratorq-TDCi (DW) diesel engine
E43283 1 2 3 4 5 6 Fuel injector 1
Fuel metering valve 2
Fuel pressure control valve 3
Fuel pump 4
Fuel rail 5
Fuel pressure sensor 6
Siemens common rail system
Lesson 2 – Fuel System
Fuel pump
Overview
Illustration shows the fuel pump with halfshaft for timing belt drive (1.4L Duratorq-TDCi (DV) diesel engine)
E53590 1 5 6 2 3 A B C 4 Fuel return A High-pressure connection B Fuel line C
Fuel metering valve (partial view) 1
High-pressure pump element (displacement unit) 2
Fuel pressure control valve 3 Eccentric 4 Halfshaft 5 Transfer pump 6
NOTE: The fuel metering valve as well as the fuel
pressure control valve are part of the fuel pump and therefore must not be renewed separately during servicing.
Note: Depending on the engine version, the fuel pump
is driven via the timing belt for camshaft drive (1.4L Duratorq-TDCi (DV) diesel engine) or via the exhaust camshaft (2.0L Duratorq-TDCi (DW) diesel engine). The design and function of the fuel pump are essentially similar.
Lesson 2 – Fuel System
Siemens common rail system
High-pressure generation and fuel routing in the fuel pump
E53591 1 10 13 14 11 9 10 10 11 11 12 13 13 4 B D 8 A C 3 2 5 7 6 Fuel line AFuel line (fuel quantity fed to the fuel pump) B
High-pressure connection to the fuel rail C
Fuel return D
Admission-pressure control valve 1
Strainer filter 2
Intake side of the transfer pump 3
Transfer pump 4
Fuel metering valve 5
Fuel pressure control valve 6
Filter 7
Fuel pump 8
Eccentric on the halfshaft 9
Pump element intake valve 10
Siemens common rail system
Lesson 2 – Fuel System
Pump element outlet valve 11
High-pressure ring line 12
High-pressure pump elements 13
Lubrication valve 14
The fuel is drawn from the fuel tank via the fuel filter by means of the transfer pump integrated in the fuel pump.
The transfer pump delivers the fuel on to the fuel metering valve and to the lubrication valve. When the fuel metering valve is closed, the admission pressure control valve opens and routes the excess fuel back to the intake side of the transfer pump.
The lubrication valve is calibrated to always ensure sufficient lubrication and cooling in the interior of the pump.
The fuel quantity fed to the high-pressure chambers (pump elements) is determined via the
electromagnetically-operated fuel metering valve (actuated by the PCM).
The high-pressure chambers are formed by three pump elements (displacement units), each offset by 120 degrees.
The fuel pressure control valve is located in the high-pressure channel, between the high-pressure chambers and the high-pressure outlet port to the fuel rail. This electromagnetically-operated valve which is actuated by the PCM controls the fuel pressure which is fed into the fuel rail via the high-pressure outlet port. The fuel pressure control valve routes the excess fuel into the fuel return line and back to the fuel tank.
Principle of high-pressure generation (intake stroke)
E53592 1 1 5 4 3 2 A B C 2 3 4 5 D Fuel intake A Fuel delivery B
Fuel feed from the fuel metering valve C
Fuel outlet port to the high-pressure ring line D Intake valve 1 Exhaust valve 2 Piston 3 Halfshaft 4 Eccentric 5
The three pump plungers are actuated by the rotary movement of the fuel pump halfshaft and the eccentric
When the fuel metering valve opens the feed to the high-pressure chambers, the fuel pressure from the
Lesson 2 – Fuel System
Siemens common rail system
high-pressure chambers. If the transfer pressure exceeds the internal pressure of the high-pressure chamber (pump plunger in TDC position), the intake valve opens. Fuel is now forced into the high-pressure chamber, which moves the pump plunger downwards (intake stroke).
Principle of high-pressure generation (delivery
stroke)
When the pump plunger passes BDC, the intake valve closes due to the increasing pressure in the high-pressure chamber. The fuel in the high-pressure chamber can no longer escape.
As soon as the pressure in the high-pressure chamber exceeds the pressure in the high-pressure channel, the exhaust valve opens and the fuel is forced into the high-pressure channel (delivery stroke).
The pump plunger delivers fuel until TDC is reached. The pressure then drops and the exhaust valve closes. The pressure on the remaining fuel is reduced. The pump plunger moves downwards.
If the pressure in the high-pressure chamber falls below the transfer pressure, the intake valve reopens and the process starts again.
Service instructions
Specific versions only:
After installing a new fuel pump, the adapted values
of the fuel metering valve must be reset with the help
of the IDS.
Fuel rail and high-pressure fuel lines
Fuel rail
Illustration shows the system in the 2.0L Duratorq-TDCi (DW) diesel engine E53593 2 3 4 1
High pressure fuel lines (to the fuel injectors) 1
High-pressure fuel line (to the fuel pump) 2
Fuel rail 3
Fuel pressure sensor 4
The fuel rail is made of forged steel.
The fuel rail performs the following functions:
• stores fuel under high pressure and • minimises pressure fluctuations.
Pressure fluctuations are induced in the high-pressure fuel system due to the operating movements in the high-pressure chambers of the fuel pump and the opening and closing of the fuel injectors.
The fuel rail is therefore designed in such a way that its volume is sufficient, on the one hand, to minimise
pressure fluctuations. On the other hand, the volume
in the fuel rail is sufficiently low to build up the fuel pressure required for a quick start in the shortest possible time.
The fuel supplied by the fuel pump flows via a high-pressure line to the fuel rail (high-pressure accumulator). The fuel is then sent to the individual fuel injectors via the four fuel injection lines which are all the same length.
Siemens common rail system
Lesson 2 – Fuel System
When fuel is taken from the fuel rail for an injection process, the pressure in the fuel rail remains almost constant.
Fuel pressure sensor
NOTE: The fuel pressure sensor must not be removed
from the fuel rail during servicing. If the fuel pressure sensor is faulty, the fuel rail must be renewed along with the fuel pressure sensor.
There is a fuel pressure sensor located on the fuel rail so that the engine management system can precisely determine the injected fuel quantity as a function of the current fuel pressure in the fuel rail (see also "Lesson 4 - Sensors").
High-pressure fuel lines
NOTE: The bending radii are exactly matched to the
system and must not be changed.
NOTE: After disconnecting one or more high-pressure
fuel lines, these must always be renewed. The reason for this is that leaks can occur when retightening due to distortion of the connections of the old lines.
The high-pressure fuel lines connect the fuel pump to the fuel rail and the fuel rail to the individual fuel injectors.
Fuel injectors
E53594 1 7 6 8 9 10 4 11 6 7 2 3 1 E D C 2 3 4 5 6 A B E D CFuel injector (1.4L Duratorq-TDCi (DV) diesel engine and 1.8L Duratorq-TDCi (Kent) diesel engine)
A
Fuel injector (2.0L Duratorq-TDCi (DW) diesel engine)
B
Fuel injector head C
Hydraulic servo system D
Fuel injector nozzle E
Connector for PCM 1
Piezo actuator 2
High-pressure fuel line connection 3
Combustion chamber seal 4
Lesson 2 – Fuel System
Siemens common rail system
Emission standard coding 5
Fuel return connection 6
Retainer 7
Fuel return adapter 8
O-ring 9
Adapter fastening clip 10
Plastic bush 11
Depending on the engine version, fuel injectors of different designs are used. Their basic construction and function are, however, largely the same.
The start of injection and the injected fuel quantity specified by the PCM are implemented by means of the piezo-electrically-controlled fuel injectors.
Depending on engine speed and engine load, the fuel injectors are actuated by the PCM with an opening voltage of approximately 70 V. The piezo effect causes the voltage within the piezo element to rise to
approximately 140 V.
The fuel injectors inject the appropriate fuel quantity per working cycle for all engine operating conditions into the combustion chambers.
Extremely short switching times of approximately 200 µs permit extremely rapid reaction to changes in the operating conditions. The fuel quantity to be injected can thus be metered very precisely.
The fuel injectors are divided into three assemblies:
• fuel injector head, including the piezo actuator, • hydraulic servo system,
• fuel injector nozzle.
NOTE: The fuel injectors cannot be dismantled during
repair as this results in their destruction.
NOTE: The wiring harness connectors of the fuel
injectors must on no account be unplugged when the engine is running. The piezo actuators remain expanded for a certain period after the power is cut off in the charging phase, i.e. the nozzles remain open. Effect: continuous injection and engine damage.
The combustion chamber seals must be renewed during servicing.
Special features
1.4L Duratorq-TDCi (DV) diesel engine:
• In newer versions, a distinction is made between
Emission Standard III and Emission Standard IV fuel injectors. A code is stamped onto the fuel injector shaft for this purpose:
– E3 = Emission Standard III, – E4 = Emission Standard IV.
2.0L Duratorq-TDCi (DW) diesel engine:
• A guide bushing located in the lower part of the
cylinder head and a plastic bushing on the fuel injector shaft serve to fasten the fuel injector.
Siemens common rail system
Lesson 2 – Fuel System
How fuel injectors work
Fuel injector closed
E53595 4 3 2 1 8 2 6 3 3 5 7 High-pressure feed 1 Control piston 2 Fuel return 3 Piezo actuator 4 Mushroom valve 5 Control chamber 6 Nozzle prechamber 7 Nozzle needle 8
The fuel is fed at high pressure from the fuel rail via the high-pressure feed into the control chamber and the nozzle prechamber.
The piezo actuator is de-energised and the orifice to the fuel return is closed by means of the spring-loaded mushroom valve.
The hydraulic force now exerted on the nozzle needle by the high fuel pressure in the control chamber via the control piston is greater than the hydraulic force acting on the nozzle needle, as the surface of the control piston in the control chamber is greater than the surface of the nozzle needle in the nozzle prechamber.
The nozzle needle of the fuel injector is closed (no injection).
