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Electronic fuel injection and engine management 217 Basic principles of EFI 218 Types of EFI systems 218 Block diagrams of an EFI system 220 Operation of a multipoint EFI system 222 Components of an EFI system 224 Engine management 229 Electronic concentrated control system 231 Sequential multipoint fuel injection system 234 Other features of engine control systems 235 Throttlebody injection (TBI) 241 Servicing engine control systems 242 Locating basic faults 244 Fault diagnosis 245 Testing equipment 246 Technical terms 248 Review questions 248
217-250_May 2chap 13 13/9/06 3:48 PM Page 217 217 Chapter 13 Electronic fuel injection and engine management Basic principles of EFI Testing equipment Types of EFI systems Technical terms Block diagrams of an EFI system Review questions Operation of a multipoint EFI system Components of an EFI system Engine management Electronic concentrated control system Sequential multipoint fuel injection system Other features of engine control systems Throttle-body injection (TBI) Servicing engine control systems Locating basic faults Fault diagnosis 217-250_May 2chap 13 13/9/06 3:48 PM Page 218 218 part two fuel and engine management Electronic fuel injection (EFI) is a fuel system for petrol engines which uses electronically controlled injectors to spray fuel into the engine’s intake manifold The system has an electronic control unit (ECU), or computer, to control injection The ECU receives input signals from various sensors, which it processes It then sends output signals which adjust the quantity of fuel being injected and, in some cases, when the fuel is injected The computer can be arranged to monitor almost all engine controls This monitoring and controlling process is usually referred to as engine management The control units of different manufacturers are called by many different names but the generic term ECU (electronic control unit) will be used in this chapter Engine management systems use electronics to not only control fuel injection, but they also control ignition and emissions for improved engine performance Basic principles of EFI The basic operation of an EFI system hinges around two main components: Electrically operated injectors, which spray fuel into the intake manifold (Figure 13.1) An ECU (Figure 13.2), which collects information from various parts of the engine and controls the fuel delivered by the injectors figure 13.2 ECU and wiring harness HOLDEN LTD EFI compared with a carburettor system Apart from the petrol tank, almost all the components of an EFI fuel system are different from those of a carburettor fuel system EFI performs the same overall functions as a carburettor, but there are a number of reasons why EFI is used One of the main reasons is that the air–fuel ratio can be closely controlled throughout the operating range of the engine This is much harder to with a carburettor, where various methods of mixture correction have to be used Types of EFI systems There are two main types of EFI The difference between the systems is the location of the injectors and their mode of injection (Figure 13.3) These two systems are as follows: Multipoint injection A separate injector is used for each cylinder, and the fuel is sprayed into the intake ports This is also called port injection figure 13.1 Fuel injector located in the manifold at the intake valve port FORD The quantity of fuel delivered by the injectors is quickly adjusted by the ECU to meet changes in engine conditions Almost instantaneous changes can be made to the quantity of fuel being delivered to the engine Throttle-body injection One or two injectors are used in a throttle body which is mounted on the intake manifold in a similar manner to a carburettor This is also called single-point injection Very simply, the throttle body and injector form an electronically operated carburettor Both EFI systems use a similar type of electronic control and their injectors operate in a similar way As well as these two systems, there are mechanical injection systems and also systems that are both 217-250_May 2chap 13 13/9/06 3:48 PM Page 219 chapter thirteen electronic fuel injection and engine management air 219 Multipoint EFI system plenum chamber special length tubes Figure 13.4 shows a basic multipoint EFI system The parts are: Air cleaner and ducts to provide clean air Airflow meter to measure the flow of air injectors injectors Throttle valve, which controls the flow of air into the engine Plenum chamber (surge tank or swirl chamber) to dampen the flow of air Fuel tank to store fuel (a) Multipoint injection injector air air intake manifold Electric fuel pump to provide pressure in the system Fuel filter to protect the injectors Fuel rail to supply the injectors with fuel Injectors that spray fuel into the intake ports 10 Pressure regulator to control the pressure in the system (b) Throttle-body injection figure 13.3 Diagrams show the difference between multipoint and throttle-body injection 11 ECU to control injection and other engine requirements Throttle-body injection mechanical and electronic EFI systems are the most commonly used; other systems will not be covered here ■ Throttle body injection is sometimes called centrepoint or central injection Figure 13.5 is a basic throttle-body, or single-point, EFI system This has the same type of supply system as a multipoint system, but it has a throttle body with an injector In both systems, the ECU is used to control the quantity of fuel delivered by the injectors electronic control unit (ECU) figure 13.4 Basic multipoint EFI system 217-250_May 2chap 13 13/9/06 3:48 PM Page 220 220 part two fuel and engine management electronic control unit (ECU) figure 13.5 Basic throttle-body injection (TBI) system EFI subsystems An EFI system has three subsystems: an air-intake system a fuel system a control system These provide the mixture of air and fuel, and control a number of other functions The basic EFI systems (Figures 13.4 and 13.5) have these three subsystems, and the parts of each can be identified on the simple diagrams All EFI systems, whether simple or complex, will have the three subsystems This is the way in which a system should be looked at, as it is easier to understand if the subsystems are examined separately Block diagrams of an EFI system An easy way to identify the components of an EFI system is by using block diagrams Figures 13.6 to 13.9 show block diagrams for the air, fuel and control subsystems of a multipoint system Airflow sensor This measures the quantity of air flowing into the system so that the correct amount of fuel can be provided for the optimum air–fuel ratio Throttle body The throttle body has a throttle valve that is operated by the accelerator pedal This controls the amount of air that enters the engine Plenum chamber This acts as a surge tank and distributes the air to the branches of the intake manifold Intake manifold The branches or pipes of the manifold carry air to the cylinders and also provide a mounting for the injectors air air cleaner airflow sensor throttle body engine intake manifold plenum chamber figure 13.6 Air-intake system In the block diagram of an air system shown in Figure 13.6, the air enters at the air cleaner and flows through the system to the engine The parts and their functions are as follows: Air cleaner This has a cellulose fibre element which provides clean air for the system Block diagram of the air system for multipoint EFI Fuel system The main parts of a return-to-tank fuel system are shown in the block diagram in Figure 13.7 Fuel tank This performs the normal function of holding fuel It has a fuel supply line and a return 217-250_May 2chap 13 13/9/06 3:48 PM Page 221 chapter thirteen electronic fuel injection and engine management 221 fuel tank assembly fuel filter fuel pump figure 13.7 pressure regulator Block diagram of a fuel system for multipoint EFI (return-to-tank system) engine line In some installations, a submerged fuel pump is fitted Fuel pump An electric pump is used This has the electric motor and pump in a common housing and operates whenever the engine is running If the fuel pump is fitted above the level of the fuel tank, an additional low-pressure pump is sometimes located inside the fuel tank to prime the main pump Fuel filter A paper filter is fitted in the fuel line so that all the fuel is filtered before it reaches the injectors Fuel rail The fuel rail, or distributor pipe, receives fuel from the filter and supplies it to the injectors All the injectors are connected in parallel with the common fuel rail Injectors These spray atomised fuel into the intake ports of the engine For each rotation of the crankshaft, each injector valve opens once, regardless of whether the inlet valve is open or not If the valve is closed, the fuel is stored in and around the inlet port until the next time the valve opens The fuel will then be drawn into the combustion chamber With this arrangement, only half the fuel requirements are injected each time injection occurs Pressure regulator The pressure regulator is fitted at the end of the fuel rail It maintains the pressure in the system high enough for injection The pressure regulator also maintains a constant pressure differential across the injector ■ This arrangement is referred to as a return-to-tank system because it has a return fuel line from the pressure regulator in the engine compartment Returnless fuel system The main parts of a returnless fuel system are shown in the block diagram in Figure 13.8 This system has figure 13.8 injectors fuel rail Block diagram of a returnless fuel system for multipoint EFI been developed in order to overcome the evaporative emission problems associated with returning hot fuel from the fuel rail back to the fuel tank The main features that are different from a return-to-tank system are: Fuel tank In this system the fuel tank also houses the fuel pump, fuel filter, and pressure regulator assembly There is no return line from the fuel rail Fuel pump The pump assembly contains the fuel filter, the pressure regulator valve and the fuel gauge sender unit (see Figure 13.33) Fuel filter The filter, as part of the pump assembly, is mounted in the fuel tank Pressure regulator The pressure regulator is part of the pump assembly fitted inside the fuel tank as shown in the diagram It maintains the pressure in the system high enough for injection Control system The electronic control system consists of a central ECU and a number of sensors and other electronic controls The sensors are shown in the block diagram in Figure 13.9 By various means, these sense or measure the conditions at their locations and this information is transmitted to the ECU ECU This is an electronic device that processes the information provided by the sensors It then allows the injectors to pulse to earth, which determines their opening period, and therefore the quantity of fuel injected Timing sensor An engine-driven sensor provides a signal which, after being processed by the ECU, is used to time the injectors Each injector could be 217-250_May 2chap 13 13/9/06 3:48 PM Page 222 222 part two fuel and engine management timing airflow air temperature coolant temperature throttle position electronic control unit (ECU) ■ Some engines have a cylinder-head temperature sensor instead of, or in addition to, the coolanttemperature sensor injectors other figure 13.9 Other sensors Other sensing devices are used for particular conditions, such as for cold starting The voltage of the electrical system is also taken into account because the state of the vehicle’s electrical system affects the operation of the injector solenoids Adjustment is made to compensate for changes in voltage Block diagram of a control system for EFI opened once per engine revolution, or once each second engine revolution Airflow sensor Already referred to as part of the air system, the airflow sensor provides a continuous measurement of all the air being taken into the system The ECU directs the injector to provide the right amount of fuel to suit the air ■ The relationship of the following should be noted: the throttle valve, which is controlled by the driver through the accelerator, determines the amount of air flow; the airflow sensor measures the air flow; and the injector provides an appropriate amount of fuel Air-temperature sensor This is installed in the airflow meter or the intake air stream to measure the temperature of the air being drawn into the system The density of air (and the amount of oxygen the air contains) is related to its temperature The ECU adjusts the quantity of fuel to suit the air density Coolant-temperature sensor This is a sensor in the cylinder head that measures the coolant temperature It enables a slightly richer mixture to be provided when the engine is cold Throttle-valve switch This is operated by the throttle-valve shaft and is used to tell the ECU when the engine is idling so that the mixture strength can be slightly adjusted The throttle sensor is also used to indicate various positions of throttle opening Operation of a multipoint EFI system Figure 13.10 shows the arrangement of a Bosch L-Jetronic fuel system This contains the three subsystems (air-intake, fuel and control) which have been previously described The principles of the L-Jetronic system have been applied to many other EFI systems and it has been developed further to include engine-management functions Bosch components, or components of similar design, are used in many other systems The operation of the system will be described, and then the components will be considered in greater detail Air-intake system The air system provides clean air to the engine and also measures air flow It operates as follows: Filtered air from the air cleaner (not shown) passes into the airflow sensor (12) The airflow sensor measures the quantity of air as it flows through This information is sent to the ECU (6) The throttle valve (11) is used by the driver to control the flow of air into the engine and so control the engine’s speed and power The position of the throttle valve is relayed to the ECU by the throttle-valve switch (10) Air passes through the plenum chamber and then into the intake manifold before entering the engine Air enters the engine through the intake valve and is mixed with fuel sprayed from the injector (7) to form a fuel charge The auxiliary-air device (18) allows extra air past the throttle valve when the engine is cold to speed up the engine This has a similar effect to opening the throttle slightly 217-250_May 2chap 13 13/9/06 3:48 PM Page 223 chapter thirteen electronic fuel injection and engine management 223 figure 13.10 Schematic arrangement of the L-Jetronic system fuel tank, electric fuel pump, fuel filter, fuel rail or distributor pipe, pressure regulator, ECU, injector, start valve, idle-speed adjusting screw, 10 throttle-valve switch, 11 throttle valve, 12 airflow sensor, 13 relay, 14 lambda or oxygen sensor, 15 coolant-temperature sensor, 16 thermo time switch, 17 distributor, 18 auxiliary-air device, 19 idle-mixture adjusting screw, 20 battery, 21 ignition starter switch BOSCH Fuel system The fuel system pumps fuel from the fuel tank and sprays it into the intake manifold through the injectors: The fuel is pumped from the fuel tank by an electric pump (2) which maintains a pressure in the system Fuel is filtered as it passes through the filter (3) into the fuel rail or distributor pipe (4) Fuel pressure is held in the fuel rail by the pressure regulator (5) The injectors are connected to the fuel rail They spray fuel into the intake manifold when directed by the ECU A start valve (8) is used for cold conditions This supplies additional fuel for starting Control system The control system receives input signals (information) from a number of sources, processes them, and sends out signals to the injectors When the ignition switch (21) is turned on, the relay (13) is energised and the ECU (6) is activated The ECU can then adjust injection to suit the information that it receives This information comes from a number of sensors: the distributor (17) for engine speed and ignition timing the airflow sensor (12) for the quantity of air (for which the right amount of fuel must be injected) the throttle switch (10) for the throttle-valve opening the temperature sensor (15) for coolant temperature the oxygen sensor (14) in the exhaust manifold, for correct air–fuel mixture the thermo time switch (16) for the length of time that the cold-start valve remains operative 217-250_May 2chap 13 13/9/06 3:48 PM Page 224 224 part two fuel and engine management Components of an EFI system The above covers the general operation of a multipoint EFI system The components will now be considered in more detail Airflow sensor The airflow sensor in Figure 13.11 consists of a flap or vane that is deflected by the flow of air through the sensor The flap is connected to the moving contact of a potentiometer (variable resistance) so that the resistance of the potentiometer is varied according to the position of the flap This provides a voltage signal that is related to air flow The ECU then adjusts the fuel from the injectors to suit the amount of air entering the engine The flap is V-shaped One part of the flap is used as an airflow valve; the other part is a compensating flap This operates in a damping chamber to dampen flap movement ■ This is a basic method of sensing air flow Other sensors are covered later Air-temperature sensor An air-temperature sensor is fitted in the intake side of the airflow sensor This measures the density of the incoming air and signals this information to the ECU The ECU adjusts the fuel to suit air density Fuel pump The fuel pump is a roller-cell electric pump (Figure 13.12) It consists of a pumping element and an electric motor in a common housing An electric pump is used because the system must be full and pressurised before the engine can be started The injectors need pressure to spray starting fuel into the intake manifold The pump has an inlet at one end and an outlet at the other Fuel flows straight through the pump, and this both lubricates and cools the pump motor A permanent-magnet-type motor is used and this drives the roller-cell pump element The roller-cell pump consists of a rotor in a housing (Figure 13.13) Slots in the rotor carry the rollers The rotor is offset in its housing to form a pumping chamber so that fuel is carried around between the rollers as the pump rotates ■ The fuel system must be pressurised before the engine can be started Fuel filter The filter is an in-line filter between the pump and the regulator It has a paper filter element as well as a screen to trap larger particles (Figure 13.14) Fuel pressure regulator figure 13.11 Airflow sensor of the flap or vane type FORD The pressure regulator (Figure 13.15) is used to maintain a regulated pressure in the system, at a nominal 250 kPa The regulator has a metal housing with a spring-loaded diaphragm When pressure builds up, the diaphragm lifts the valve to return surplus fuel back to the tank The pressure is set during manufacture and is determined by the strength of the spring The chamber above the diaphragm is connected to the intake manifold, and so subject to manifold vacuum Changes in manifold pressure will therefore vary the pressure in the fuel system However, with this arrangement, the pressure difference across the injector valves is held constant With the pressure 217-250_May 2chap 13 13/9/06 3:48 PM Page 225 chapter thirteen electronic fuel injection and engine management figure 13.12 Roller-cell electric fuel pump assembly figure 13.13 Roller-cell pump element figure 13.14 Fuel filter for an EFI system 225 FORD FORD figure 13.15 BOSCH constant, the quantity of fuel injected is related only to the time that the injector is open ■ This is a return-to-tank fuel system with the pressure regulator at the end of the fuel rail Fuel injector The location of the injector of a multipoint system was shown in Figure 13.1 It is fitted in the intake manifold so that the fuel is sprayed directly into the intake port Fuel-pressure regulator for an EFI system FORD in the cylinder head The fuel is directed in a finely atomised form with a spray angle of about 25° The atomised fuel is maintained in suspension in the air Wetting the surfaces of the manifold and valve port is avoided because this would leave unmixed fuel This fuel would not be fully burnt in the combustion chamber and would contribute to hydrocarbon emissions in the engine’s exhaust The injector is fitted into the manifold in special rubber mouldings which protect it from heat and 217-250_May 2chap 13 13/9/06 3:48 PM Page 226 226 part two fuel and engine management vibration It has an electrical connection and a fuel connection A section through an injector is shown in Figure 13.16 Fuel is supplied through the top of the injector and retained in the injector by the needle valve, which is held on its seat by the spring At appropriate times, electrical pulses from the ECU energise the solenoid windings and attract the plunger and needle away from its seat As a result, a spray of fuel is directed into the intake port of the engine ■ The needle has a very small lift When fully open, this is only about 0.1 mm As well as these, there are a number of compensating signals, such as engine temperature and air temperature, for which the air–fuel mixture is modified from that used for normal operation The ECU provides for a basic amount of fuel to be delivered by the injectors, and this is then varied to suit the different operating conditions The distributor is used to signal engine speed and also the crank-angle position for injection timing The pulse signal is passed through a pulse-shaping circuit in the ECU, which changes it from peaks into a rectangular form (Figure 13.17) The pulse is then used to operate the injectors figure 13.17 Pulse signal to the injectors – pulse width can be varied, as shown by (a) and (b), for different engine conditions In the diagram, each rectangular pulse represents the opening of an injector The height represents voltage, and the width represents time The ECU widens the pulse for higher loads and increases the frequency of the pulse for higher engine speeds At low engine loads, the pulse is narrow, so only a small quantity of fuel is delivered by the injectors Figure 13.18 shows the main inputs and outputs of an EFI control system, while the diagram in Figure 13.19 illustrates how the ECU adjusts to suit different operating conditions Engine-temperature sensor figure 13.16 Section through a fuel injector for multipoint EFI TOYOTA Electronic control unit (ECU) The ECU receives two main signals: engine speed the amount of air taken in by the engine A rich air–fuel ratio is needed for cold starting and for warming up, so the ECU needs to know the engine temperature This signal is supplied by the engine coolanttemperature sensor (Figure 13.20) The temperature sensor is screwed into the engine block or cylinder head with its end extending into the water-jacket The end of the sensor is a thermistor with a negative temperature coefficient The resistance of the sensor decreases as its temperature increases This change in resistance is used to measure engine temperature 217-250_May 2chap 13 13/9/06 3:49 PM Page 236 236 part two fuel and engine management ignition switch combination meter power steering oil pressure switch battery check engine warning light circuit opening relay engine ECU VSV (for EVAP) airbag sensor assembly camshaft position sensor throttle position sensor charcoal canister DLC3 fuel pump air conditioner amplifier camshaft timing oil control valve airflow meter air–fuel ratio sensors DIS ISC valve injector air WT air cleaner knock sensor crankshaft position sensor figure 13.31 water temp sensor A schematic diagram of an EFI and the engine management system Modes of injection There are four different modes of injection Continuous Injector sprays continuously and the flow rate is controlled to suit the load and speed of the engine Usually found only on older model vehicles Simultaneous All injectors operate at the same time and inject once for each revolution of the engine Sequential Injectors are arranged to operate in a sequence that follows the firing order of the engine Grouped (banked) Injectors operate in groups that follow the firing order of the engine For example, in a two-bank system for a six-cylinder engine, heated oxygen sensors TOYOTA injectors 1,5,3 are grouped to operate together followed by 6,2,4 Figure 13.36 shows the basic wiring diagrams for simultaneous, sequential and grouped modes The ECU controls the injectors by completing the circuits to earth For Figure 13.36(a), all the injectors will operate at once For Figure 13.36(b), each injector can be operated independently, and for Figure 13.36(c), the injectors can only be operated as groups of three Synchronous and asynchronous injection With synchronous injection, the operation of the injectors is synchronised to the speed of the engine ... 218 part two fuel and engine management Electronic fuel injection (EFI) is a fuel system for petrol engines which uses electronically controlled injectors to spray fuel into the engine? ??s intake... fuel supply line and a return 217-250_May 2chap 13 13/9/06 3:48 PM Page 221 chapter thirteen electronic fuel injection and engine management 221 fuel tank assembly fuel filter fuel pump figure... thirteen electronic fuel injection and engine management 14 Distributor Provides engine- speed signals and crank-angle signals 15 Knock sensor and knock control unit Detects detonation and signals