Diesel Engines: Fuel System Diagnosis and Repair (16)
Some electronic unit injectors require the setting of the EUI plunger height. How is this done?
1. A mechanical adjustment is performed by adjusting an adjustable screw on the rocker arm. 2. Since plunger height affects timing, this should be accurately adjusted. 3. Adjustment methods vary according to engine design; methods include torque wrench, dial indicator, and height adjustment gauges. 4. Manufacturers' procedures must be followed for each design.
What does the fuel subsystem used with EUI fueling consists of?
1. A suction and charge circuit with fuel movement provided by a positive displacement gear-type pump.
What do actuator tests allow you to do?
1. Allows you to command the various actuators and 1. observe their operation. 2. An example of this is the injector solenoid tests performed with the key on and the engine of (KOEO). 3. When you select this test, the ECM actuates each injector solenoid in sequence, and their operation may be verified because they are heard. 4. This is referred to by one manufacturer as a buzz test. 5. Another example is performed with the key on and the engine running. (KOER) and is referred to as a cylinder cutout test. 6. Either one or multiple cylinders are cut out, and their effect on idle speed and their relative contribution to engine power output is calculated. 7. Similar testing of actuators is available - not only the engine but other systems, such as anti-lock brake systems (ABS), AS WELL. 8. You can make a multitude of tests using a single attachment to the self-diagnostic terminal.
What are some of the tests that can be performed with a voltmeter
1. Are available voltage at the battery and source voltage at virtually and any electrical component. 2. The voltmeter can also be used to indicate resistance when performing voltage drop testing.
What are engine protection systems designed to do?
1. Are designed to lower horsepower and torque when the ECM recognizes that the engine is overheating, overspeeding, or has low oil pressure. 2. These systems use the sensors already installed on the engine to determine these operating conditions. 3. The manufacturers may flash a light on the dash or send a message to the driver information display to alert the operator that the engine is operating at reduced power output.
What are automatic stop/restart systems designed to do?
1. Are designed to reduce idling times. 2. They are generally set to maintain the cab temperature to a comfortable level while the driver is sleeping in the bunk. 3. These systems typically have a switch on the hood to send an "open hood" signal to the ECM. 4.This signal prevents system operation for safety.
What should you do before making a connector repair?
1. Be certain of the type of connector. 2. Weather-pack and pull-seal connectors look similar but are serviced differently.
There is no appropriate way to mechanically short out an EUI, so when a cylinder misfire is being diagnosed, how does the ECM electronics perform this task?
1. By electronically cutting out the EUI in sequence and analyzing the performance effect.
How can you located restricted fuel filters?
1. Can be located by performing a pressure-drop test across the filter. 2. The normal maximum filter restriction is 5 psi. 3. Low power and low boost pressure are the most common fuel filter restriction concerns.
What does insufficient fuel flow result in?
1. Can result in low power and fuel starvation. Fuel starvation has been associated with many fuel pump failures on diesel engines.
How must care be taken during installation of fuel filters?
1. Care must be taken to prohibit unintentional dirt ingestion. 2. Most OEMs now recommend installing the filter dry and using the fuel system to prime the filter. 3. This prevents unfiltered fuel from entering the system.
Why are open circuits often difficult to locate by sight during diagnosis?
1. Due to oxidation or because the terminal alignments is hidden by the connectors. 2. Merely wiggling a connector on a sensor in the wiring harness may correct in open-circuit condition. 3. This should always be considered when an open circuit or failed sensor is indicated. 4. Intermittent problems may also be caused by oxidized or loose connections.
Where are ECM cooling plates mounted and what are they used for?
1. ECM cooling plates are mounted under the ECM and have fuel flowing through them. 2. The fuel is used to cool the ECM. 3. They can also become restricted and result in low-power.
What the ECM harness do electrically?
1. Electrically connects the ECM to other modules in the vehicle engine and passenger compartments. Wire harnesses should be replaced with proper part number harnesses. 2. When signal wires are spliced into a harness, use wire with high temperature insulation only. 3. With the low current and voltage levels found in the system, it is important that the best possible bond at all wire splices be made by soldering the splices.
When the ECM commands an engine to run a specific RPM, how is an injector cut-out test performed.?
1. First the average duty cycle of the EUI in milliseconds is displayed. 2. If the engine RPM is to be maintained during the test (normally run at idle or 1,000 rpm), as each EUI is cut out electronically by the ECM, the pulse width (PW) of the remaining injectors will have to lengthened if engine RPM is held at the test value. 3. This would be true until a defective EUI was cut out. 4. In this case, there would be no increase in the average PW of the operating EUI.
How should you check for the presence of water in fuel tanks?
1. First, allow them to settle, and then insert a probe (a clean aluminum welding rod) lightly coated with water-detection past through the fill neck until it bottoms in the base of the tank. 2. Withdraw the rod and examine the water detection paste for a change in color. 3. This test will give some idea of the quantity of water in the tank by indicating the height on the probe the colr has changed to. 4. Trace quantities (just the tip of the probe changes) in fuel tanks are not unusual and will not necessarily present any problems.
What are the advantages that voltage drop testing to measure resistance over using an ohmeter.
1. First, it is very accurate. You can find very small resistances where voltage is lost (dropped) passing through connections, relays, switches, fuses, wiring, and other voltage conveying components in the circuit. 2. Another advantage is that it is a dynamic test, performed with the circuit live and under load. 3. It is not necessary to isolate the component being tested from the circuit by disconnecting or removing it. 4. simply connect the voltmeter in parallel with the portion of the circuit being tested, being careful to observe polarity.
What should stop/restart systems be inspected for?
1. For loose wiring, connection and mounts. 2. The systems can be tested using the scan tool. 3. Components are replaced, not required.
What should you routinely inspect fuel tank vents for?
1. For restrictions and protected from ice buildup. 2. A plugged fuel tank vent will rapidly shut down an engine, creating a suction-side inlet restriction value that the transfer pump will not be able to overcome.
What are fuel heaters?
1. Fuel heaters are electrical resistance heaters and can be checked with an ohmmeter or ammeter. 2. The ECM typically controls these based upon temperature. 3. if the heaters fail to operate, fuel gelling can occur in cold weather. If these heaters fail to shut off, they can lead to low-power concerns because of overheated fuel.
How much of the fuel pumped is cycled through the fuel system and returned to the tank and what is the excess fuel used to do?
1. Generally, 1/2 to 2/3 of the fuel 2. Is used to lubricate and cool high pressure injection components, especially those exposed directly to the extreme temperatures of engine cylinders.
Why is it recommended that a high-impedance digital voltmeter be used whenever working with trucks that have electronic modules or computer management systems?
1. High impedance meters will have very high resistance, typically 10,000,000 ohms internal resistance, compared to analog meters, which generally have only 10,000 ohms internal resistance. 2. This is important to prevent unintended damage to the system being tested.
What can excess pressure or flow in the drain system be an indication of?
1. Is an indication of a failed injector, pressure relief valve, or a restricted drain line. 2. On some of these systems, a drain test is performed individually on each item to determine the failed component.
How is the fuel sending unit and integral assembly flange fitted to the tank?
1. It consists of a float and arm connected to a variable resistor. 2. As the float arm is moved through its stroke, the resistance changes, producing a reading at the dash gauge that correlates with fuel quantity.
When codes are present, what is it usually useful to do?
1. It is usually useful to record the codes, clear them, and retest to see whether they reappear. 2. Codes that reappear indicate an active code that should be repaired before proceeding . 3. Most self-diagnostics will provide a data stream that enables you to observe the input values from each of the related sensors and switches. 4. Any values suspected to be in error should be verified using a DMM.
When a vehicle runs out of fuel and it is determined that the fuel subsystem requires priming, remove the filters and fill with filtered fuel? What is the recommended priming procedure?
1. Locate a bleed point in the system (on an in-line injection pump system, this will usually be at the exit of the charging gallery) and crack open the coupling. 2. Next, if the system is equipped with a hand-primer pump, actuate it until air bubbles cease to exit from the cracked open coupling. If the system is not equipped with a hand-primer pump, fit one upstream from the secondary filter and actuate until air bubbles cease to exit from the cracked-open coupling. 3. Retorque the coupling. Crank the engine for 30-second segments with at least two-minute intervals between crankings until it starts. This will allow for starter motor cool-down. In most diesel engine systems, the high-pressure circuits will self-prime once the subsystem is primed. Because fuel lubricates the fuel system components, some fuel systems are prone to damage from running out of fuel.
How to install high-pressure fuel lines?
1. Make sure that the clamps holding the lines together are tight. High-pressure fuel lines must be installed as a set. It is much easier than installing them individually. 2. Wiggle the high-pressure fuel injection lines into position on the engine; Start from the back and go toward the front of the engine. 3. Install the injection lines onto the injection pump and tighten the brackets holding the high-pressure fuel lines to the intake manifold. 4. Connect the high-pressure fuel injection lines to the fuel injectors one at a time, starting with cylinder #1. Do not remove the caps from the fuel lines or components until they are ready to be connected. This will help prevent introducing dirt into the system. 5. tighten the fuel injection line to the injector nuts. Do not overtighten. This may collapse the sealing nipple, reducing flow to the nozzle. 6. Install the low=pressure fuel lines and filter assembly back on the engine. Tighten the nuts to specifications. 7. Run the engine and check for leaks.
What are precautions you should know about priming a fuel system?
1. Most OEMs prefer that the technician avoid pressurizing air tanks to prime a fuel system. 2. Diesel fuel contains volatile fractions. 3. The act of pressurizing a fuel tank with air pressure will vaporize some fuel, while air exiting an air nozzle creates friction. 4. This could potentially start a fire, so this practice should be avoided, especially in extremely hot weather conditions.
What are the different methods to check for air in the fuel?
1. One method involves installing a clear piece of hose or liquid eye in the fuel supply line, running the engine and looking for bubbles in the fuel stream. 2. Another method is to remove the return fuel hose and submerge it in fuel, and look for bubbles. 3. Some manufacturers provide a test port at the fuel filter where this same test can be performed. 4. With all these tests, there should be no bubbles in a properly operating system.
How should you remove high-pressure fuel lines?
1. Remove the low-pressure or leak-off fuel lines if used. 2. Disconnect the fuel injection lines at the injectors. Cap each injection line and injector. 3. Disconnect the fuel lines at the fuel injection pump. Cap each injection line and pumping element as the line is removed to prevent the entry of dirt into the system. Once removed from the engine, individual fuel lines can be removed from the assembly for replacement. When ordering parts, each line is different and cannot be interchanged; therefore order lines individually for the particular cylinder of the line.
Describe the EUI.
1. The EUI is a cam-actuated, integral pumping, metering, and atomizing device that is controlled by the vehicle management computer or ECM. 2. The pumping element of an EUI consists of a plunger and barrel. 3. The barrel is the stationary member of the pumping element. 4. The plunger is the reciprocating member, and it is spring loaded into its retracted position. 5. The plunger is actuated by cam profile. 6. The injector camshaft may be mounted on the cylinder block or overhead. 7. When the injector train is actuated by cam profile, the EUI plunger is driven through its stroke. 8. This means that the actual plunger stroke does not vary regardless of how the engine is being fueled.
How do diesel engines use drive-by-wire technology?
1. The accelerator pedal position (APP) sensor connects to the accelerator pedal and serves as an input, telling the ECM the throttle request by the operator. 2. There is not a throttle cable connecting the accelerator pedal to the fuel system on these engines. 3. The throttle position sensoR (TPS) attaches to the throttle valve (throttle plate) on engines so equipped, and sends a signal to the ECM telling the position of the throttle valve. 4. The electronic throttle valve is opened and closed by an electric motor operated by the ECM. 5. The ECM uses this throttle valve to aid in EGR FLOW. 5. The APP and TPS are traditionally potentiometers. They can have up to three potentiometers and may or may not be coupled with an idle validation switch (IVS). 6. If the APP or TPS is adjusted, it is normally adjusted to approximately 1 volt at idle. 7. If replacement is necessary, the APP and TPS can usually be replaced separately from the accelerator pedal or throttle valve.
Most trucks are equipped with either a six-pin or nine-pin Deutch SAE/ATA Jj1587/J1708/J1939 connector, which is usually just referred to as the ATA connector. Where is this connector located and what does it do?
1. The connector will be located in the engine compartment or in the dash, usually to the left of the steering column. 2. This common connector and the software protocols are established by agreement, which enables proprietary software used by various OEMs to communicated with and at least read the parameters and conditions of their competitor's systems. 3. Most engine-management systems must also communicate with other chassis systems to optimize engine performance.
What does the common rail fuel system consist of?
1. The fuel tank, filter, low-pressure pump, high-pressure pump, high-pressure junction block, high-pressure common-fuel rail or rails, fuel injectors, and fuel cooler. The common rail system typically has a supply pump and a high-pressure pump. 2. The high-pressure pump is of a radial design using two or three pistons. 3. The pump pressurized the fuel in the range of 5,000 psi to 30,000 psi. 4. The high-pressure fuel travels from the pump to the high-pressure rail(s). 5. The fuel pressure in the high-pressure rail(s) is controlled by the ECM. 6. Some models will use both volume and pressure-control valves. 7. When fuel pressure drops in the high-pressure rail(s), the ECM allows more fuel to flow into the high-pressure pump. 8. The junction block has a pressure relief valve that will open in case of fuel system overpressurization (approx 32,000 psi). 9. This overpressurization would only occur in case of a failure of the system and is not a normal operating condition. 10. The fuel rails connect to each individual injector, sometimes through fuel lines; other times, the rail sits directly on top of the injector. 11.The fuel injector is typically a solenoid-operated device that is opened by the ECM to allow fuel to flow into the combustion chamber.
Fuel supply systems have a low-pressure side and a high-pressure side. How would you check the low-pressure side?
1. The low-pressure side will have a restrictor fitting or regulating valve to control the pressure. 2. These valves can leak or stick open or shut. 3. When the valve sticks, the open fuel pressure will be lower than normal and can cause low power. 4. If the valve is stuck shut, the fuel pressure will be higher than normal, which can overheat the fuel and lead to low power and damaged fuel system components.
3. The two test leads are commonly red and black. What do they do?
1. The red lead is attached to the most positive (higher potential) portion of the circuit. 3. The black lead may be connected to a good ground or to a point on the circuit with lower voltage (lower potential) than the red lead, depending on the type of being performed. 4. This places the meter in parallel to the portion of the circuit being tested and is sometimes referred to as a shunt. 5. For the meter to indicate a voltage, the circuit should be turned on and have current flowing. 6. Most modern meters have additional features that make them more useful, like autoranging, touch hold. and min/max, so learn how to use your meter as effectively as possible.
Modern truck electronic systems electronically store customer options. What are they used for?
1. These are used to change the operational characteristics of the chassis electronic system. 2. To access and reprogram this information, connect a diagnostic tool to the data link usually located under the dash on the driver's side. 3. Examples of customer parameters that can be changed using the appropriate software include maximum road speed, tire size, axle ratios, driver reward profiles, idle shut-down time, automatic stop/restart, variable horsepower, torque curve, and progressive shifting.
What is the function of fuel coolers that are used in some systems?
1. These coolers are fuel-to-air; some models are mounted in areas where they are easily contaminated with mud.
How can you access information from the truck electronic control modules?
1. This may be accomplished using each manufacturer's specific electronic service tools (EST) or by using PC-based software that is available by license agreements from each manufacturer. 2. Aftermarket generic scan tools are also widely used. 3. Each manufacturer's ESTs and PC-based software by the agreement will access and retrieve information from other manufacturers' products; some information is regarded as proprietary, however, so each usually features self-diagnostics that greatly exceed the minimum requirements.
Most fuel systems now incorporate a priming pump. How are they used?
1. This pump can be either manually or electrically operated. 2. They are used to prime a fuel system and remove the air. 3. A bleeder screw is often included, which enables air to escape when loosened. 4. When fuel without air bubbles exits the screw, the fuel system has been bled, and the screw can be tightened. 5. Primer pumps are usually replaced when defective, but some OEMs offer repair kits.
How would you use an ammeter?
1. To use an ammeter, you must disconnect a wire and connect the meter into the circuit. 2. With the meter in series with the rest of the circuit, all of the current flowing must pass through the meter. 3. If the current exceeds the capacity of the meter, it will be damaged. 4. For this reason, digital meters are usually protected by internal fuses. 5. if current exceeds the fuse rating, it will blow and the meter stops working.
What do some connectors, such as the coolant sensor use?
1. Use terminals called micro connector. 2. They are released by inserting a fine pick tool through the front of the connector to disengage a locking tab on the terminal. 3. To remove, bend the tab toward the terminal and then pull the terminal and wire out of the connector. 4. To install, insert the tool into a new connector and bend the tab away from the terminal. 5. Molded plugs and connectors are factory-fabricated and must be spliced into the harness. 6. Ensure correct splice procedures are used to make a good electrical connection.
What does molded-on connectors usually require?
1. Usually require complete replacement of the connector. 2.This means splicing a new connector assembly into the harness. 3. Use care when probing a connector or replacing terminals in them - it is possible to short between opposite terminals. 4. Use jumper wires between connectors to check circuits. 5. Never probe through the weather pack seals. 6. A connector test adapter kit is used to probe terminals during diagnosis. 7. a fuse remover and test tool should be used when removing a fuse.
What is voltage drop?
1. Voltage drop is the amount of electrical pressure lost or consumed when pushing current through the circuit. 2. Voltage drop occurs when current passes through load components and resistances. 3. Most of the voltage should be dropped across the load and not across the components that convey voltage and control the load.
In a diesel fuel subsystem, there is a clear divide between what two sides and what terms are used to describe each?
1.Between the suction side and the charge side, represented by the fuel transfer pump. 2. The terms "suction circuit" and "charge circuit" are used to describe each.
What do high-pressure lines, fittings and seals need to be inspected for?
1.For leaks. 2. Mounting hardware should be tight, secure and complete. 3. Loose mounting hardware must be repaired or replaced. 4. Failure to do so will result in vibration damage to these components.
What can cause low supply-pump pressure/flow?
> Can be caused by the normal problems of restricted fuel filters, > a worn pump > and insufficient fuel in the tank.
What are high-pressure common rail fuel systems tested for?
> For supply-pump pressure and flow; >high-pressure pump pressure; > and sometimes drain-system pressure and flow.
What do you use to identify low-pressure problems?
A fuel pressure gauge.
Which filters are usually located on which side?
A primary filter is usually located on the suction side of the transfer pump, while the secondary filter is located on its charge side.
What is useful for measuring larger current flow?
An inductive pickup is useful. A big advantage in using one one is that it may be clamped over almost any portion of the circuit without the need to disconnect anything to place the meter in series in the circuit.
What are Hydraulic Electronic Unit Injector (HEUI) fuel systems checked for?
Are checked for supply-system fuel pressure as well as the correct oil pressure in the high-pressure oil rail.
How is fuel used as a cooling medium?
As a cooling medium, the fuel transfer heat from the injection devices to the fuel tank. This provides the fuel tank(s) with a role as heat exchanger.
How is fuel from the fuel subsystem typically provided to the EUI?
By means of a manifold integral with the cylinder head. Fuel is routed through the EUI for purposes of fueling the engine, with excess fuel used to lubricate and cool.
What can cause low pressure from the high-pressure pump?
Can be caused by low supply-pump pressure or flow > a weak high pressure pump > a faulty fuel-pressure control valve (pressure limiter) > or a faulty pressure-relief valve. 2. The drain system is checked for excess pressure and flow.
What are the types of fuel supply pumps?
Can be electrical and mechanical.
Many manufacturers now use an on/off switch to activate PTO mode. How can this switch also be used?
Can be used to raise or lower the RPM during PTO mode. This is usually a momentary switch The ECM is constantly monitoring these sensors for a faulty signal. If a faulty signal is detected, the ECM will set a DTC and may operate the engine in a limp home mode.
What can air in the fuel system cause?
Can cause low power and surging RPM. Hard starting, especially after the vehicle has been sitting, can be caused by air in the fuel system.
What is the result of restricted fuel coolers?
Can result in overheated fuel and low power.
What functions does the DMM combine?
Combines the functions of the voltmeter, ohmmeter, and ammeter in one housing.
The scan tool and ECM can also be used to perform a cylinder contribution test with the engine running. How is this test performed?
During this test, the ECM turns the injectors off one at a time or in groups in order to determine their level of contribution to engine performance. The scan tool and ECM can also be used to drive the injection actuation oil pressure to preprogrammed levels and observe the injection actuation control valve and injection-actuation pressure sensor for appropriate responses.
What are the most important component for fuel system life?
Fuel filters. 2. The technician needs to be vigilant while servicing the fuel filter to ensure top-quality filters that meet all OEM requirements are installed.
How are fuel pickup tubes position?
Fuel pickup tubes are positioned so that they draw on 1. fuel slightly above the base of the tank and thereby avoid picking up water and sediment. 2. Fuel pickup tubes seldom fail, but when they do, it is usually by metal fatigue crack at the neck. This results in no fuel being drawn out of the tank by the transfer pump whenever the fuel level is below the crack.
How would you perform fuel pressure tests?
Fuel pressure tests are performed using the appropriate fuel pressure gauge and specifications. 2. These tests often require the engine to be operated under full load. 3. If a dynamometer is not available, the vehicle can be road tested while a second technician monitors the pressure on the gauge.
What is used to remove water from the fuel?
Fuel water separators. These filters should be drained at each service interval and as indicated by the WATER IN FUEL (WIF) lamp on the dash. 3. if the WIF lamp comes on during operation, the driver should immediately stop and drain the filter.
Where is fuel stored on commercial vehicles?
In fuel tanks. Many diesel fuel management systems are designed to pump much greater quantities of fuel through the system than is actually required to fuel the engine.
What is low fuel-supply pressure a common cause of?
Low power/low turbocharger boost pressure concerns.
What is the typical limit of most digital meters.
Measuring about 10 amps.
What is the function of the remote (from the tank) fuel transfer pumps on most commercial pumps?
Most commercial truck fuel subsystems use remote (from the tank) fuel transfer pumps and not assemblies that incorporate the sending unit and a transfer pump.
What is measured in ohms or fractions of an ohm?
Resistance. The ohmmeter, which is self-powered, passes a very small current supplied by an internal battery through the circuit being tested.
What do some manufacturers use instead of potentiometers for their APP and TPS and how does it work?
Some manufacturers are using a Hall-effect switch. These sensors send a digital signal instead of an analog signal. Electronic throttle and PTO control devices are typically replaced, not repaired.
What are precautions when inspecting for high pressure leaks on a diesel engine?
Technicians should never use their hands when inspecting for high pressure leaks on a diesel engine. The high-pressure fuel can be injected into the skin and cause sickness or death.
Why should you not attempt to test a live circuit; that is one that has voltage in it from any source other than the meters battery?
Testing a live circuit can damage an ohmmeter.
If a 4 cylinder engine had one dead EUI, what would occur?
The following would occur if an injector cutout test sequence was performed with the engine running at 1,000 rpm. 2. To run the engine at 1,000 rpm, the three functioning EUIs would produce fueling values read in PW milliseconds that would be averaged on the display. 3. When one of the functioning is electronically cut out by the ECM, only two EUIs would be available to run the engine at the test speed of 2,000 rpm, causing the average PW to increase. 4. As each functioning EUI was cut out in sequence, the average PW would have to increase to maintain the test RPM. 5. However, when the defective EUI was cut out, there would be no change in the average PW, because it was based on the engine running on three cylinders.
How is amperage testing different from voltage testing?
The meter must be place in the circuit in series (unless you are using an inductive pickup, which measures current flow by measuring the strength of the magnetic field produced?
What must you remember concerning the values that you are observing?
The values are those that the computer receives. They are subject to the computer's sampling rate and may be influenced by the integrity of the wiring and connectors that convey them.
What is the voltmeter for?
The voltmeter is a high-resistance meter, so it can be placed across various power sources without damage to the meter.
Why should the driver not pour a product in the fuel tank that indicates it will remove water?
These products tend to force the water through the injection system and can damage the system.
Knowing what amount of source voltage is being lost or dropped in a circuit overcoming resistance is often helpful. What is this measured as?
This measured as voltage drop.
The HEUI injectors can be tested electrically using a "click" or "buzz" test. How is this test performed?
This test is performed key on engine off using the scan tool to activate the injector solenoids with the ECM while the technician listens for an appropriate click or buzz.
Why is it important to choose the correct range for accurate testing of a wide range of resistance values?
When a range that is too low is used, the meter may falsely indicate an infinite resistance. Start with the highest range and move to a lower scale if a very low reading is obtained. Autoranging meters will select the correct scale. It is frequently necessary to remove the component being tested or otherwise isolate it from the circuit to get accurate results.
What will a totally failed APP cause?
Will cause the engine to be limited to idle RPM only. Voltage output from the sensors can be measured with a voltmeter to determine if the sensor, wiring or ECM is at fault.
How can fuel sending problems be diagnosed?
With a DMM in resistance mode by moving the float arm through its arc and observing readings.
What are the key components of the common-rail system?
· Are the injectors. · They are fitted with a rapid-action valve (solenoid valve or piezo-triggered actuator) which opens and closes the nozzle. This permits control of the injection process for each cylinder. All the injectors are fed by a common fuel rail, this being the origin of the term "common rail".
In the common-rail fuel-injection system, the functions of pressure generation and fuel injection are separate. How does each of them work?
· The injection pressure is generated independently of the engine speed and the injected fuel quantity. · The electronic diesel control (EDC) controls each of the components · Pressure generation and fuel injection are separated by means of an accumulator volume. Fuel under pressure is supplied to the accumulator volume of the common rail ready for injection.
What main component groups does the common-rail system consists of?
· The low-pressure stage, comprising the fuel-supply system components. · The high-pressure system, comprising components such as the high-pressure pump, fuel rail, injectors, and high-pressure fuel lines. The electronic diesel control (EDC), consisting of system modules, such as sensors, the electronic control unit, and actuators.
What is the main advantage of the common rail system?
· The main advantage of the common[1]rail system is its ability to vary injection pressure and timing over a broad scale. This was achieved by separating pressure generation (in the high-pressure pump) from the fuel-injection system (injectors).
How does the common-rail system adapt fuel injection to the engine?
· This is achieved by: · High injection pressure up to approx. 1,600 bar, in future up to 1,800 bar. · Injection pressure adapted to the operating status (200...1,800 bar). · Variable start of injection. Possibility of several pre-injection events and secondary injection events (even highly retarded secondary injection events)
