LV24 diesel fuel systems (2)

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kap all phase & 6/11/03 11:36 am Page 17 Student Workbook LV24 Diesel Fuel Systems (2) LV24/SWB Student Workbook for Technical Certificates in Light Vehicle Maintenance and Repair MODULE LV24 DIESEL FUEL SYSTEMS (2) Contents Page Safety Precautions: Foreword 3 Routine Maintenance: Filter replacement Filter construction Filter replacement notes – applicable to all types Filter replacement – paper type element Filter replacement – cartridge type Filter replacement – sandwich type Water contamination Draining water Additional fuel filters Fuel System Bleeding: Low pressure system – vacuum type Low pressure system – pressure type Bleed points High pressure system Bleeding the system Bleeding procedure – vacuum type systems Bleeding procedure – high pressure system Progress check Page Control Cable Adjustment: Pre-checks- throttle cable Cable adjustment Drive belt adjustment Adjustment mechanisms Timing errors Drive belt tension adjustment 22 23 24 25 26 27 28 Injector Maintenance/Cleaning: Fuel additives Chemical cleaners Ultrasonic cleaning Stripping and cleaning Injector testing Nozzle opening/break-off pressure Injector noise Spray patterns Nozzle leakage Leak-back 30 30 31 31 32 32 33 33 34 34 35 Compression Testing: Manual method Electronic method 36 36 37 10 11 12 13 14 15 15 16 17 17 18 19 20 21 -1Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Page Servicing/Maintenance Checks: Pipelines Checking pipelines Return pipe/hoses Progress check 38 39 39 40 41 Glow Plug and Circuit Testing 42 Fuel Injection Faults: Failure to start Engine starts then stops Difficulty starting Erratic running/surging Bluish/white exhaust Black exhaust smoke Diesel knock 44 44 45 45 46 47 47 48 Diesel Fuel and Emissions: Boiling point range Cetane number Flash point Cold flow properties and filtration Other additives 49 49 49 50 50 50 Page Environmental Issues: EU emissions standards for passenger cars Carbon monoxide (CO) Nitrogen oxide (NOx) Carbon dioxide (CO2) Particulate matter (PM) Hydrocarbons (HC) Principles of combustion Ignition delay Flame spread Direct burning After burn Progress check -2Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue 51 51 52 52 52 52 53 53 53 54 54 55 56 Safety Precautions Foreword Diesel fuel systems operate at both low and extremely high pressures Some components have fluid connections to both low and high-pressure sections and it is sometimes easy to confuse the two, especially in adverse working conditions A leak in the low pressure system can produce an intense spray of fuel and it is therefore advisable to apply the same precautions to all parts of the fuel supply system Routine Maintenance Routine maintenance of diesel engines is an important factor in the reliability and longevity of diesel engines With proper maintenance these engines will run for many thousands of miles, often under harsh driving and environmental conditions If they are not looked after however, small faults can lead to serious engine damage in a very short time Many diesel engines are fitted to small commercial vehicles (mainly light vans), which may be driven by a number of people who not actually own the vehicle or have an interest in its running This can lead to longer than normal service intervals and missed maintenance Routine maintenance is much more than simply following a list of “things to do” A skilled technician will spot potential problems early, allowing prompt action to prevent more complicated faults developing -3Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Filter replacement Fuel filters prevent potentially damaging particles getting into the sensitive components of the diesel injection system and as such are a vital part of the diesel fuel system, and they need to be replaced at regular intervals Just by doing the job they were designed to do, that of preventing anything other than clean fuel proceeding further along the fuel system towards the engine, they retain these particles and will eventually become clogged Filters will naturally retain almost any foreign bodies entering the fuel system including particles of dirt, fluff from rags and paint flakes from the inside of tanks and cans In some cases, when the temperature is very cold, typically below –15°C, the filter may also retain crystal deposits formed from natural waxy elements within the fuel itself Over time the flow of fuel through the filter will be reduced by the particles retained within the element, and when this flow reduction reaches a critical point the lack of fuel flowing to the injection system will eventually promote engine misfiring, stalling and even non-starting This is the point at which the filter is often described as being “blocked” In many fuel injection systems the fuel serves as a lubricant and damage can be caused to vital components if the fuel flow is sufficiently reduced by blocked filters Service intervals are designed to help ensure that the filter is replaced before the build-up of dirt etc within the filter becomes excessive Water is often present in diesel fuel, normally caused by condensation in the vehicle fuel tank and in tanks where the fuel is stored prior to reaching the vehicle Most filter assemblies incorporate a drainage system to allow water to be removed at regular intervals and to drain the assembly when replacing the filter Water collecting in the system is damaging to injection system components and may cause engine running/starting problems -4Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Filter construction Diesel fuel filter construction varies between manufacturers and three main types are in use today Paper element type – disposable paper element enclosed within a sealed filter housing or bowl The housing may be screwed directly to the filter head or secured by a bolt between the housing and the filter head Cartridge type – disposable, metal cased cartridge screwed directly to the filter head Sandwich type – disposable, metal cased cartridge with exposed ends, clamped between the filter head and sediment bowl by a long bolt -5Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Rubber sealing rings are normally fitted between the filter or filter bowl and the filter head Filter elements may have rubber seals attached to them and sealing rings are also normally installed where bolts pass through the filter It is normally recommended that these seals are replaced at the same time as the filter and in some cases they may be included as part of a replacement filter kit Filter replacement notes – applicable to all types Before any dismantling is attempted remove the fuel filler cap – during normal running a small amount of pressure may build up in the tank and fuel lines This pressure may force fuel out of the system when components are removed with an associated risk of injury Removing the filler cap first will ensure that this pressure is released before any dismantling takes place Disconnect any electrical cables which may be attached to switches/sensors on any part of the filter assembly which is turned or unscrewed when the filter is removed – some filters require many turns to unscrew them fully and wiring or components may be damaged if they are twisted during filter removal Additionally, disconnect any wiring attached to components in the area if there is a risk that they may be damaged in the filter changing process -6Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Place a suitable container beneath the filter bowl to catch any fluid drained In some cases it may not be possible to catch the fluid directly beneath the filter due to lack of space In these cases it will difficult to prevent fluid splashing onto other mechanical and electrical components and/or paintwork Where spillage is unavoidable the use of rags in the area may be necessary to reduce splashing and a drip tray should be used to prevent fluid reaching the floor Clean any spillage from vehicle components and the working area Take careful note of the position and orientation of any clips, springs and washers during dismantling so that the assembly can be re-built correctly – it is possible that incorrect assembly can cause blockages, air leaks or even a total lack of filtering Before disposing of the old filter element and seals, use them as patterns to check that the replacements are of the same size and type Dispose of the old filters according to local regulations and procedures -7Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Filter replacement – paper element type See the filter replacement notes above Some filter bowls incorporate a drain plug or tap and in certain cases a drain hose may also be fitted Where possible, drain the fluid from the filter into a suitable container by partly unscrewing the plug/tap Tighten the plug/tap when all the fluid is drained in order to prevent spillage of any remaining fluid when the filter is finally removed Tightening the plug/tap at this stage has the added advantage of reducing the chance of forgetting to tighten it later Remove any drain hoses at this stage if there is a chance they may be twisted during filter removal Where the filter bowl is screwed directly to the filter head, unscrew the entire bowl and remove it to a drip tray If the bowl is too tight to remove by hand, use a strap wrench Alternatively, the filter bowl may be held in place by a bolt, fitted either downwards through the filter head into the filter bowl or upward from the bottom of the filter bowl into the head Remove this bolt, noting the position of the filter and that of any seals or washers and place the filter bowl in a drip tray In some cases, the filter element is held in place by the filter bowl itself and removing the bowl will normally allow the element to be removed at the same time Sometimes however, the filter element will remain attached to the filter head by a bolt, threaded sleeve or nut after the bowl is removed Where applicable remove the fixing and filter element, noting its position and avoiding any fuel spillage Note the position of any seals or washers during removal -8Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Clean the filter bowl, seal recesses and fixings with a lint-free rag and replace any damaged seals or gaskets Some seals are normally replaced as a matter of course even if they appear undamaged, particularly the seal between the edge of the bowl and filter head Before disposing of the old filter element and seals, use them as a pattern to ensure that replacements are of the same size and type Fitting the new filter is the reverse of removal Apply a smear of clean diesel fuel to the seal between the filter bowl and the filter head to help the bowl seat itself properly To save time and effort when priming the system later, partly fill the filter bowl with clean diesel fuel at this stage, allowing for displacement of fuel by the filter itself This may not be possible, especially when the bolt securing the filter bowl passes all the way through the bowl Carefully fit the filter and bowl, ensuring they seal together properly without over-tightening Make sure the filter is fitted the correct way up – some filters will be marked Use the manufacturers’ recommended torque settings when finally tightening any securing nuts or bolts If the whole filter bowl is screwed on, use hand effort only -9Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Glow Plug and Circuit Testing Diesel fuel does not ignite particularly easily in cold conditions The electrical glow system is designed to pre-heat the combustion chamber in order to assist starting, particularly when the engine is cold Simple versions of the system are powered from the vehicle battery and consist of a relay, necessary due to the high current often involved and a number of glow plugs/heating elements with their tips protruding into the engine’s combustion chambers In most systems, sophisticated timer/control units are used to improve the efficiency of the system Testing the glow system consists mainly of checking that power is reaching the various components at the right time, ensuring earth connections are in good condition and all components are operating as expected: • Main relay – normally has a permanent power supply, a switched power supply (when the ignition is on), an earth and a power output to the control unit • Timer/control unit – needs a power supply from the main relay output, an earth connection and controls the power output to the glow plug relay (this relay is often incorporated in the control unit) • Glow plug relay – receives power from the timer/control unit and switches the high current required by the glow plugs This has a power feed from the battery and an earth connection -42Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Testing varies from vehicle to vehicle but is normally carried out using a voltmeter, ammeter and ohmmeter in the following general order: Ensure the battery is in a good state of charge Check for a power supply (voltmeter) at the glow plugs when the glow system is on (only for a few seconds after the ignition is turned on) If power is not available here it will be necessary to check the relay and control unit power supplies and earths Check the total current drawn by all the glow plugs together using an ammeter Most ammeters utilise a clamp which should be fitted around ALL the wires to the glow plugs Disconnect ONE glow plug, leaving the clamp in place If that glow plug is good, the current should drop in proportion to the number of cylinders, i.e 25% on a four-cylinder engine Disconnect a second plug; the current should drop by a further 25% in this case If disconnecting a glow plug produces no current drop, the plug is not working Remember that the ignition should be turned off between each disconnection to allow the system to re-set itself and reduce the chance of accidental short circuits If an ammeter is not available it will be necessary to disconnect all the plugs and check the resistance (ohmmeter) between each plug’s wiring connection and the body of the glow plug or cylinder head Compare the resistance with specification, a faulty plug will normally be open circuit -43Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Fuel Injection Faults Diesel engines have no ignition system, therefore engine combustion problems can be generalised into the areas of: • Too little fuel • Too much fuel • Fuel arrives in the cylinder too early • Fuel arrives in the cylinder too late • Insufficient compression Failure to start • Insufficient fuel in tank - ensure that there is enough fuel in the tank Be careful when the vehicle is not on level ground, if the fuel level is low fuel may not reach the pick-up pipe • Faulty stop control cable/solenoid operation - ensure that the engine stop control operation is functioning, and is in the "running" position • broken fuel injection pump drive - check by removing the fuel injection pump drive cover, turning the engine to check that the pump drive/belt is serviceable See also “Difficult starting” -44Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Engine starts then stops • Insufficient fuel in tank - ensure that the fuel level in the tank is sufficient A low fuel level may allow air to be drawn into the system only occasionally, stopping the engine • Air in fuel system - bleed the fuel system as instructed in the relevant service literature Check low pressure fuel pipes on suction side, for hairline cracks or loose connections allowing air into the system, rectify as necessary • Blocked fuel tank vent - check and rectify as necessary • Blocked fuel filter/s - check and renew as necessary • Restriction in fuel return pipe - ensure that the fuel return pipe from the injection pump to the tank is not damaged or partly blocked, restricting fuel return • Restriction in the induction system - check air cleaner/element, re-new if dirty Ensure that no restriction is present in air induction piping • Sticking injector/s – clean/overhaul/replace See also “Difficult starting” Difficult starting • Air in the fuel system - bleed the system of air • Restricted fuel feed pipe or blocked vent in the fuel tank - trace and rectify restriction or blockage • Blocked fuel filters - renew fuel filter element(s) • Defective fuel lift pump - check lift pump operation, if insufficient fuel is flowing, repair or replace fuel lift pump • Incorrect fuel pump timing - check all aspects of fuel pump timing according to the relevant manual • Defective or incorrect injectors - Replace or service all the injectors • Defective fuel injection pump - remove pump for attention by specialised workshop or fit replacement pump See also “Failure to start” -45Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Erratic running/surging • Defective stop control cable/solenoid operation, sticking throttle or restricted movement - ensure that the operation of these is free, and are not fouling in any way • Restriction in the induction system - check air cleaner element, renew if dirty ensure that no restriction is present in induction piping and manifold • Air in the fuel system - bleed system • High pressure fuel pipes - ensure that these are of the correct type and are fitted in the correct firing order • Blocked fuel tank vent – rectify • Restricted fuel feed pipe – repair • Blocked fuel filter – replace • Defective fuel lift pump - check lift pump operation, if insufficient fuel flow is evident, remove lift pump and rectify or fit replacement • Incorrect fuel pump timing – check and adjust as necessary • Defective injectors – clean/replace as necessary See also “Difficult starting" -46Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Bluish/white exhaust smoke Incorrect fuel pump or valve timing – typically retarded Check/adjust timing according to appropriate service literature Defective or incorrect injectors – clean/replace as required Water in the fuel – will also cause misfiring Drain water from system Black exhaust smoke • Restriction in the induction manifold - check air cleaner/element condition • Check for dents or kinks in the hoses or pipes and examine the induction manifold for any obstructions • Fuel injection pump fuelling settings incorrect – re-calibrate pump • Incorrect fuel injection pump timing - check all aspects of fuel pump timing according to the service literature • Defective or incorrect injectors – clean/replace as required • Restriction in the exhaust system -47Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Diesel knock • Incorrect fuel pump timing – check/adjust the timing according to appropriate service literature • Defective or incorrect injectors – clean/replace as required • Incorrect type or grade of fuel - check that the fuel being used is the correct specifications See appropriate service literature Some operators still add petrol to diesel fuel in winter to aid starting/running When using modern diesel this is no longer necessary and may lead to injection system damage • Defective (leaking) or incorrect type of injectors – to determine if an injector is responsible, slacken off the high-pressure pipe of each injector in turn to eliminate "knocking" whilst running engine at high idle If the knock ceases when loosening a particular injector fuel pipe then that injector is probably faulty Repair/replace injectors • Incorrect fuel pump timing or incorrect valve timing - check all aspects of fuel pump and valve timing according to the relevant service literature -48Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Diesel Fuel and Emissions Boiling point range Hydrocarbon (HC) based fuels are normally made up of a mixture of different basic hydrocarbon elements Each hydrocarbon element has a different boiling point and in diesel fuels these mixtures usually result in the boiling point ranging from around 180ºC to 380ºC Adjusting the proportion of the hydrocarbons in the fuel to reduce the boiling point improves the fuel’s operating properties in cold conditions but may reduce its lubricating qualities, risking increased wear of the fuel injection system The ignition quality of the fuel is also reduced (see “cetane number”) Conversely, increasing the boiling point of the fuel improves the lubrication quality and ignition quality but usually results in higher soot emissions and carbon contamination of the engine components Cetane number The cetane number is a measure of the ability of a diesel fuel to burn spontaneously and immediately when injected into the hot, compressed air in the combustion chamber (ignition quality) National and international standards apply to the cetane rating, which is determined by testing in a standard test engine For clean, smooth engine operation a cetane number above 50 is necessary for fuel supplied in Europe The cetane number may be as low as 45 when the fuel is used in arctic conditions as the processes used to make the fuel flow in cold conditions usually reduce its ignition quality -49Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Flash point The flash point is the temperature at which vapour emitted to the atmosphere from a liquid fuel can be ignited by a spark This has implications for transport and storage of diesel fuels and they must not have a flash point below 55ºC It used to be commonplace for operators to add petrol to diesel fuel in cold conditions in order to improve the cold starting of some engines Adding just 3% petrol is sufficient to reduce the flash point to around room temperature, making storage and handling of the fuel extremely hazardous Fortunately, modern fuels conforming to legal standards contain chemicals which make adding petrol to diesel fuel unnecessary Cold flow properties and filtration Diesel fuel contains paraffin, which at low temperatures can crystallise and result in blockages in the vehicle’s fuel filtration system This paraffin crystal precipitation is sometimes known as “waxing” Under some conditions waxing can occur at ambient temperatures as low as 0ºC, making the addition of cold flow-improving chemicals necessary even in temperate, European climates These additives are normally added to the fuel at the refinery in the country of use and not actually prevent waxing but they limit the size of the paraffin crystals, allowing them to pass through the filtration system without causing blockages Other additives A number of additives are necessary to improve the performance of diesel fuels in specific conditions These are added as packages depending on the expected operating conditions in the country of use The total concentration of these packages rarely exceeds 0.1% of the fuel and has little effect on the fuel’s physical characteristics, e.g density, viscosity and boiling point range • detergents – used to help keep the intake system and prevent deposits of carbon on the injectors and in the combustion chamber • corrosion inhibitors – help prevent corrosion of metallic components caused by moisture entering the system • anti-foaming agents – used to reduce the tendency of diesel fuel to froth or foam when agitated, e.g during re-fuelling -50Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Environmental issues Various countries have promoted the use of more environmentally friendly diesel fuel In these fuels the aromatics and sulphur content is reduced and the boiling point is lowered However, the use of special additives is required to prevent wear and other damage to diesel fuel systems caused by some or all of these changes EU emission standards for passenger cars, g/kg Exhaust gas Year Carbon monoxide(CO) Hydrocarbons+oxides of nitrogen (HC+Nox) Oxides on nitrogen (NOx) Particulates (PM) Units Euro Euro Euro Euro 2DI 1999 2000.01 2005.01 Euro 2IDI Parts/million 1992 1996 (ppm) g/kg 2.72 1.0 1.0 0.64 0.50 g/kg 0.97 0.7 0.9 0.56 0.30 g/kg - - - 0.50 0.25 g/kg 0.14 0.08 0.10 0.05 0.025 -51Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Carbon monoxide (CO) This gas is considered the most deadly of the automobile emissions There is a very good reason for this as it hinders the blood’s ability to carry oxygen throughout the body, and high exposure can lead to death CO is created by the incomplete combustion of fuel CO emissions increase in cold weather due to more fuel being required by the engine, and the catalytic converter and oxygen sensor work less effectively at low temperatures Nitrogen oxide (NOx) NOx is the collective name for the gases containing nitrogen and oxygen These gases tend to be colourless and odourless and are formed when diesel is burnt When these gases are combined with hydrocarbons and are exposed to sunlight, ground level ozone is formed which is the main component of photochemical smog Photochemical smog causes and exacerbates respiratory problems and stings the eyes It also damages plant life, including crops for human consumption Carbon dioxide (CO2) This comes from burning fuel and is a leading contributor to the greenhouse effect that is starting to destabilise our planet The greenhouse effect leads to an increase in the global temperature that amongst other things melts the ice caps and raises sea level Particulate matter (PM) This is the solid matter and liquid droplets found in the air The individual particles are extremely small and can access our lungs, aggravating asthma and other respiratory problems High long-term exposure can result in premature death -52Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Hydrocarbons (HC) Hydrocarbons are blends of hydrogen and oxygen that in many instances are carcinogenic They mix with oxides of nitrogen and in the presence of sunlight form photochemical smog Hydrocarbons along with other exhaust emissions are believed to contribute to acid rain and global warming Principles of combustion There are four phases of combustion that occur within the diesel engine, ignition delay, flame spread, direct burning and after burn They all occur over a very small crankshaft angle and the amount of time in between the following phases would have to be measured in milliseconds Ignition delay Ignition delay is the phase where the diesel has just been injected into the swirl chamber in various sized droplets None of the droplets have ignited yet as they are still in the process of absorbing the heat that has built up inside the swirl chamber The smaller droplets rise in temperature at a quicker rate than the bigger droplets due to their lesser ability to dissipate heat due to their smaller surface area -53Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Flame spread Flame spread is the phase where the smaller droplets of diesel have actually ignited and they are in the process of rapidly increasing the temperature of the swirl and the combustion chamber This is going to warm up the larger droplets to a sufficient temperature where they are just about to ignite Direct burning During this phase all of the fuel in the swirl and combustion chambers has been ignited Any fuel that is injected into the swirl chamber is igniting instantaneously due to the very high temperatures present, typically 500 800°C -54Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue After burn During this phase the diesel has stopped being injected and due to the swirl that is occurring throughout the combustion chamber the flame is travelling around mopping up left over patches of unburnt fuel This burning is occurring as the piston is moving down the cylinder There is a small amount of pressure still acting upon the piston at this point, driving it down before it gets to the exhaust stroke -55Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue Progress check Answer the following questions: Why are glow plugs commonly fitted to light vehicles? What is a cetane number? List three commonly used additives to diesel fuel? Is there any flame within the swirl chamber during the after burn phase of diesel engine combustion? -56Copyright © Automotive Skills Limited 2003 All Rights Reserved LV24: Diesel Fuel Systems (2) Issue ... Reserved LV24: Diesel Fuel Systems (2) Issue Additional fuel filters Many diesel fuel injection systems are fitted with additional filters, normally located in the connection where the fuel feed... Reserved LV24: Diesel Fuel Systems (2) Issue Control Cable Adjustment Most diesel fuel injection systems use a system of cables and linkages to connect the driver’s controls to the high-pressure fuel. .. Rights Reserved LV24: Diesel Fuel Systems (2) Issue Fuel System Bleeding Bleeding becomes necessary when air enters the fuel system This can happen when the vehicle runs out of fuel, during servicing/repair