Diagnostic of Diesel Engines

Embed Size (px)

Citation preview

  • 7/30/2019 Diagnostic of Diesel Engines

    1/14Fault Finding Training for Common Rail Diesel Injection 2

  • 7/30/2019 Diagnostic of Diesel Engines

    2/14

    Fault Finding Training for Common Rail Diesel Injection 3

    CONTENTS

    1. INTRODUCTION........................................................... ........................................................... ..................4

    2. DEFINITION OF VARIOUS LOW PRESSURE FUEL SUPPLY PRINCIPLES ................................4

    2.1. ELECTRICAL PUMP .....................................................................................................................4

    2.2. INTEGRATED MECHANICAL PUMP .....................................................................................5

    2.3. FUEL REHEATING ........................................................................................................................6

    2.3.1. Electrical Reheating........................................................... ..............................................................6

    2.3.2. Natural Reheating .............................................................. ..............................................................6

    3. DEFINITION OF VARIOUS HIGH PRESSURE REGULATION PRINCIPLES ...............................7

    3.1. GENERAL INFORMATION ABOUT HIGH PRESSURE .......................................................7

    3.1.1. Injector Control Via Leak Monitoring ............................................................. ................................7

    3.2. HIGH PRESSURE LEAK REGULATION ................................................................................8

    3.2.1. Fuel Cooling Circuit ............................................................ ............................................................9

    3.2.2. Pressure Regulator ............................................................ ..............................................................9

    3.3. REGULATION BY INTAKE FLOW LIMITATION .............................................................10

    3.3.1. Fuel Flow Actuator ............................................................. ...........................................................11

  • 7/30/2019 Diagnostic of Diesel Engines

    3/14

    Fault Finding Training for Common Rail Diesel Injection 4

    1. INTRODUCTION

    Currently, all diesel vehicles are fitted with common rail diesel injection systems.

    These systems provide increased driving pleasure, better fuel consumption andreduced pollutant emissions.However, identifying the faulty component can be difficult when a problem occurs.Given the high cost of replacing a component, correct fault finding is essential.Correct operation of the common rail system mainly depends obtaining conforminghigh pressure in the rail.Achieving high pressure may vary slightly from one system to another. Knowledge ofthese systems makes it easier to find the faulty component in the event of a problem.First, perform preliminary checks before undertaking fault finding on the fuel circuit(conformity of fuel, battery voltage, charge circuit, ignition circuit, etc.).

    2. DEFINITION OF VARIOUS LOW PRESSURE FUEL SUPPLYPRINCIPLES

    Routing of fuel from the fuel tank to the high pressure pump is essential in order toreach the correct high pressure.Components such as:

    Pipes,

    The filter,

    And the low pressure pump

    may affect the high pressure value.Several assemblies are possible on the low pressure section.

    2.1. Electrical Pump

    Some systems use an electrical pump to routefuel to the high pressure pump.

    It may be controlled in one of two ways:

    Continuously with the engine running; acalibrated valve located in the fuel filter unitregulates the low pressure to 2.5 bar.

    Or with the starter engaged in order to primea low pressure mechanical pump. In thiscase, the electrical pump is used to reach apressure of 4 bar in the rail when the ignitionis switched on. This value can be verifiedwith the fault finding tool.

  • 7/30/2019 Diagnostic of Diesel Engines

    4/14

    Fault Finding Training for Common Rail Diesel Injection 5

    2.2. Integrated Mechanical Pump

    Fuel may be supplied by a mechanical pump integrated into the high pressure pump.

    These systems canbe identified by thepresence of amanual priming bulbbefore the filter.

  • 7/30/2019 Diagnostic of Diesel Engines

    5/14

    Fault Finding Training for Common Rail Diesel Injection 6

    2.3. Fuel Reheating

    In subzero temperatures, the fuel must be reheated in order to avoid clogging thefilter. The temperature increase is achieved by either increasing the pressure in therail or by electrical resistance.

    2.3.1. Electrical Reheating

    2.3.2. Natural Reheating

    1: To high pressure pump,2: Control valve,3: Thermostatic valve,4: Reheating circuit output,5: Fuel return input,6: To fuel tank,7: Filter element,

    8: Fuel inlet.

    In order to re-heat the fuel at lowtemperatures, readmitting the fuelcoming from the return circuit isalso possible.It is at a higher temperature sinceit has been pressurised.A thermostatic component locatedin the filter allows for fuelrecirculation.

    An electrical device located onthe filter unit re-heats the fuelbefore it enters the high

    pressure pump.

  • 7/30/2019 Diagnostic of Diesel Engines

    6/14

    Fault Finding Training for Common Rail Diesel Injection 7

    3. DEFINITION OF VARIOUS HIGH PRESSURE REGULATIONPRINCIPLES

    3.1. General information about high pressure

    High pressure is at the centre of the common rail system. It can only be correct if:

    The pump is able to provide the necessary quantity of fuel,

    the high pressure system contains no abnormal pressure loss.

    3.1.1. Injector Control Via Leak Monitoring

    An injector is opened due to differential pressure by creating a leak in the upper

    section of the injector.A controlled solenoid valve releases the higher pressure A of the needle in order toraise it under the effect of lower pressure B.Example: BOSCH injector

  • 7/30/2019 Diagnostic of Diesel Engines

    7/14

    Fault Finding Training for Common Rail Diesel Injection 8

    Example: DELPHI injector valve

    3.2. High Pressure Leak Regulation

    One way to regulate high pressure in the rail is to create a leak at the high pressurepump outlet.The pressure regulator controls the leaked fuel sent to the return in order to maintainpressure in the rail.

    1: Fuel tank,2: Low pressure electrical pump,

    3: Fuel filter unit,4: High pressure pump,

    When the injector is not

    controlled, the release valvemust be perfectly airtight up tovery high pressure values. Thisprevents a leak of high pressureA to the return.

  • 7/30/2019 Diagnostic of Diesel Engines

    8/14Fault Finding Training for Common Rail Diesel Injection 9

    5: Pressure regulator,6: Rail,7: Injectors,8: Rail pressure sensor,

    9: Fuel temperature sensor,10: Fuel reheating circuit,11: Fuel return cooling circuit,12: Priming valve.

    3.2.1. Fuel Cooling Circuit

    For some applications, the high pressure leak regulation system requires the use of acooling circuit for fuel returning to the tank. In fact, much of this fuel comes from thehigh pressure system at a temperature of nearly 90C.A thermostatic component closes the passage in the cooler for temperatures below0C.If there is no fuel, a valve located on the filter unit forces passage in the cooler inorder to prime the circuit.

    3.2.2. Pressure Regulator

    The high pressure generated bythe pump (orange) is deviated tothe return (yellow). Electricalsupply of the regulator modifiesthe return passage section.

  • 7/30/2019 Diagnostic of Diesel Engines

    9/14Fault Finding Training for Common Rail Diesel Injection 10

    3.3. Regulation by Intake Flow Limitation

    The other means of regulating high pressure is to only compress the quantity neededto maintain the setting in the rail.This means offers the following advantages:

    decreased pump drive torque providing improved fuel consumption,

    lower fuel return temperature.In this case, the component that regulates rail pressure is called a fuel flow actuator.

  • 7/30/2019 Diagnostic of Diesel Engines

    10/14Fault Finding Training for Common Rail Diesel Injection 11

    3.3.1. Fuel Flow Actuator

    Low pressure coming from the fuel pump arrives on the actuator in A.The computer controls the actuator in order to limit the quantity that enters the highpressure pumping components in B.The larger the quantity admitted, the higher the pressure in the rail.In resting position (or when disconnected), the actuator is in maximum flow position.

  • 7/30/2019 Diagnostic of Diesel Engines

    11/14Fault Finding Training for Common Rail Diesel Injection 12

    Appendix 1: Test Summary

    Regardless of the system involved, fault finding always starts by checking thelow pressure fuel system.

    The first high pressure test consists of verifying the natural potential of the

    high pressure pump. This refers to its ability to pump fuel under pressure.

    Input flow monitoring systemDisconnect the fuel flow actuator andblock engine start (use commandmode or disconnect the injectors). Notethe pressure value when the starterkicks in. (In fact, the actuator is open

    when it is resting. Thus, the pumppumps its full capacity.)The pressure value must be greaterthan 1050 bar for a K9K engine, andgreater than 800 bar for an F9 or G9engine. (Minimum speed with thestarter engaged in compliance withrequirements specified in thedocumentation).

    High pressure leak monitoring systemTo perform the test, engine startingmust be blocked (e.g. by disconnectingthe cylinder reference sensor)With the starter engaged, the pressurein the rail must be greater than 300

    bar.(Minimum speed with the starterengaged in compliance withrequirements specified in thedocumentation).

    Testing the natural potential of the high pressure pump

  • 7/30/2019 Diagnostic of Diesel Engines

    12/14Fault Finding Training for Common Rail Diesel Injection 13

    The next step of the high pressure test is performed to make sure the injectorvalves are sealed. If they are not, this can cause a loss of high pressure and anegative result when testing the natural potential of the high pressure pump.

    To perform this test, measuring cylinders are attached to the return circuit of each

    injector to check that the quantity is correct.

    K9K Engine (DELPHI)

    The test is performed by first letting theengine run at idle speed for 2 minutes.Next, use the fault finding tool to startthe command two times in a row. Theengine performs a series ofacceleration actions and the fuel

    pressure is controlled at high values.After the test, the quantity measuredfor each of the injectors must notexceed the expected value (whichvaries according to the engine; refer tothe appropriate documentation).If the engine does not start, performthe test with the starter engaged asdescribed in the documentation.

    F9 and G9 Engines (BOSCH)

    The test is performed at idle speed orwith the starter engaged. (Enginewarm)A conforming injector delivers anextremely small quantity of fuel duringreturn corresponding to normal

    opening of the valve.But a faulty injector delivers a verylarge quantity of fuel.

  • 7/30/2019 Diagnostic of Diesel Engines

    13/14

  • 7/30/2019 Diagnostic of Diesel Engines

    14/14

    Checking flow correction one injector at a time.The BOSCH injection system balances the flow of each injector.It analyses combustion using the engine speed sensor signal. Thus, if combustion is

    incorrect, the computer corrects the injector flow on the cylinder in question to try tore-establish correct combustion balancing.The flow correction value can be viewed for each cylinder using the fault finding tool.The normal value is on the order of 1 mm

    3/stroke. A correction equal to +/-5

    mm3/stroke indicates a problem.

    A problem in combustion may be due to a problem involving:

    valve clearance,

    compression,

    an injector that is blocked (open or closed),

    incorrect injector positioning, etc.

    HIGH PRESSURE TEST SUMMARY TABLE:(After checking low pressure)

    Natural Pump PotentialTest

    Injector Valve Sealing Test Faulty Component

    OK OK None

    Not OK Not OK Injector

    OK Not OK Injector Not OK OK Pump

    IMPORTANT:

    Following component replacement after fault finding, the tests must be repeated inorder to check the repair.In fact, a second fault may have been masked by the first fault.