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09-01-2011, 06:04 PM


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The fuel injection system supplies the engine with a combustible air-fuel mixture. Modern cars have a digital engine control system. It controls the ignition and the fuel injection systems.
Technological developments in the automobile field resulted in the digital fuel injection system. The digital Fuel injection system is a solution to all the problems of carburetor. The controller in a Digital Fuel injection system is an electronic control module or the ignition and Fuel Injection System. Various components of the engine and fuel system send electrical signals to the ECM and ECM continuously calculates how much fuel to inject. It then opens thee fuel injectors so proper amount of fuel sprays out to produce the desired air- fuel ratio.
The seminar and presentation aimed at discussing the various parts of the digital fuel injection system.

.rar   digital fuel injection system.rar (Size: 2.85 MB / Downloads: 438)
passwordConfusedeminar and presentationproject and implimentations

All the combustion engines are design on the principle that they use some fuel as the intake and convert this into energy, to produce work. A mixture of fuel and air is a must for any combusting engine to function. Over a period Technologies have changed and evolved methods to “Feed” this mixture to the engine.
The fuel injection system supplies the engine with a combustible air-fuel mixture. Old petrol Engine cars used to the conventional carburetors for supplying air-fuel mixture to the combustion Chamber. The Carburetor technology was found insufficient to cater to the needs of the challenging environment and has many this advantages like low fuel economy, High pollution rate, delayed starting, etc.
Technological development in the automobile field resulted in the digital fuel injection system. The digital fuel injection system is a solution to all the problems of carburetor. The controller in a Digital Fuel Injection System is an electronic control module (ECM) or electronic control unit (ECU) the ECM controls the ignitions and fuel injection systems. Various Components of the engine and fuel system send electrical signals to the ECM and ECM continuously calculates how much to eject. It then opens the fuel injectors so the Proper amount of fuel sprays out to produce the desired air-fuel ratio.
The Digital fuel Injection System lacks a carburetor. It incorporates an injector similar to that in a diesel system, through which petrol is sprayed into the intake manifold. The ECM acts as the command centre and the decision is made based on the data supplied by seven sensors provided at deferent locations on the chassis.
In the Digital Fuel Injection System the mixture of fuel and air reaches the piston head in predetermined ratio. This mixture is then fed in to the combustion chamber. Once inside the combusting chamber it ignites with the help of a spark from the spark plug. As the ignition is turned on, The sensors are activated and the fuel is sent through injectors directly to the combustion chamber where it is sprayed on top of the piston heads. The air is taken separately through a set of valves. The fuel and air are mixed just before entering the combustion chamber. In the Digital Fuel Injection System the injectors are controlled by an Electronic sensor which is turned to the throttle.


Figure: 1-2

The mane important components of the Digital Fuel Injection System are:-
1) Electronic Control Module (ECM)
2) Electronic Engine Controls (EEC)
3) Sensors

The nerve centre of the Digital Fuel Injection System is the Electronic Control Module (ESM) and all the data collected from the various sensors are directed towards ECM. It serves as the processor or decision maker in an Electronic Control System.
The mane parts of an ECM are the IC Chips that contain the microprocessor and the memory. The microprocessor is the Central Processing Unit (CPU). It is the solid-state devise that control information flow in a computer. By following a set of instructions called program, The micro processor does the calculation and make the decisions solve. The microprocessor chip is sealed in a protective package or career. The signals from the sensors are received and sent through connections or terminals in the ECM. The information needed by the microprocessor is stored in an electronic storage device called a memory.
The Random Access Memory may be volatile or non-volatile. A volatile memory stores information’s temporarily, as long as battery power is available. The information stored in a non-volatile memory is not lost by disconnecting the battery. The Look up Tables of ECM is an non-volatile type memory.

The Electronic Engine Control (EEC) usually controls the fuel and injection systems. The input devices are sensors and the output devices are actuators. The EEC allows the engine to operate as fuel efficient as possible.

A sensor is a device that receives and reacts to a signal. This may be a change in pressure, Temperature or voltage. The ECM then calculate for how long to open the injectors.

The various sensors that report to the ECM includes

1) Engine speed sensor
2) Oxygen sensor
3) Manifold absolute pressure (MAP) sensor
4) Engine coolant temperature sensor
5) Intake air temperature (IAT) sensor
6) Camshaft position (CP) sensor
7) Throttle position sensor (TPS)

The ECM continuously receives all this data and checks this data with other data stored in look-up tables in the memory then the ECM decides to open the injectors and for how long.


Figure: 1-4


Figure: 1-3

The engine speed sensor is actually a crank shaft position sensor that tells the ECM how fast the engine crank shaft is turning. The ECM uses this data to control fuel metering, ignition spark advance, and the shifting of electronic automatic transmissions and transaxles.
Crankshaft position sensors are either Hall-effect sensors or magnetic sensors. In the case of Hall-effect switch the ECM count the number of crankshaft rotations per second. The crankshaft harmonic balance carries three vanes which pass between a permanent magnet and a transducer and the magnetic field transistor on and off, switching the signal voltage to the ECM. The ECM counts this voltage pulses to determine the crankshaft speed.

The oxygen sensor is installed in the exhaust manifold or exhaust pipe. It measures the amount of oxygen in the exhausted gas. It is used primarily as a means of controlling exhaust a emissions by keeping the air-fuel ratio close to 14.7:1.
The oxygen sensor is about the size of as spark of plug and produces a small voltage when exposed to oxygen. This varying voltage is sent to the ECM, the voltage varies with the amount of oxygen in the exhaust. Oxygen sensor voltage is between 1.3V and 1.5V and when the voltage is close to 0.45V, the air-fuel ratio is close to ideal 14.7:1. If the voltage is higher then 0.45V, the oxygen content is low i.e. the air-fuel ratio is rich and if the voltage is less then 0.45V the oxygen content is high and the air fuel ratio is lean.
The varying voltages tell the ECM whether the air-fuel mixture is rich or lean. The ECM then adjusts the duty cycle of the fuel injectors. It then turns them on for a longer or shorter time, each time they open. This enriches or leans out the air fuel mixture. The oxygen sensor will not work unless it is hot. It must be between 200o and 800o. While the engine is warming up, the electronic engine- control system is in open loop mode.
As soon as the engine and the oxygen sensor reach operating temperature, the oxygen sensor voltage signal is sent to the ECM. The ECM switches to closed loop mode and begins using oxygen sensor to compute injector duty cycle.

MAP sensor is a semi conductor that senses change of pressure in the intake manifold and relays it to the ECM as digital signal. The ECM gets an accurate value as to the volume of air in the intake manifold and pressures.

Intake manifold is measured in two ways:-
1) With a vacuum gauge
2) With a manifold absolute pressure gauge.

The two gauges are basically the same. Both have a flexible diaphragm that separates the two champers in the gauge. The difference is that one chamber of the vacuum gauge is open to the atmosphere. One chamber of absolute pressure gauge contains a vacuum.
The vacuum gauge compares atmospheric pressure with intake manifold pressure. The manifold absolute pressure gauges Computer the actual pressure in the intake manifold with the vacuum. This is more accurate.

The coolant temperature sensor is a thermistor that continuously reports engine coolant temperature to the ECM. This is a varying voltage signal that the ECM uses in deferent ways. If the coolant temperature is low, the ECM signals the fuel metering system to supply additional fuel for cold engine operation. The ECM also alters the ignition time to suit the engine temperature.
Most transverse engine uses an engine cooling fan. When the engine is cold, no cooling is added. The fan does not run when the engine gets hot. The signal from the coolant temperature sensor may cause the ECM to turn on the fan.

Changing air temperature, changes the density of air. Hot air at low atmospheric pressure is less dense and contains less oxygen than as equal volume of cooler air under high atmospheric pressure.
The intake air temperature sensor is a thermistor. Its electrical signal decreases as its temperature increases. The IAT sensor is located after the air filter and helps to compute actual density of air at the intake manifold. The IAT sensor sends varying voltage signals to the ECM and so it knows the air temperature.


Figure: 2-6
The air temperature sensor uses a thermistor that loses resistance as it is heated


Figure: 2-8

Rotary throttle position sensor
As the throttle position changes, the wiper blade moves which changes the voltage signal to the ECM.
This varies from about 5 volts at wide-open throttle to a fraction of a volt at closed throttle.

The Camshaft position sensor informs the ECM of the position of the cylinders and the engine speed. This information is often crucial in deciding the direction and the amount of the fuel injected as well as the ignition advance and the control of the knock through ECM in the absence of a knock sensor.

The throttle body contains the throttle valve. The assembly usually mounts on the intake manifold. The throttle valve connects by linkage to the accelerator pedal. Depressing the accelerator pedal opens the throttle valve.
The ECM must always know the position of the throttle valve. A TPS on the throttle body continuously reports throttle position to the ECM. The position of throttle valve is important in the control of the idle speed and in the sharp patterns of automatic transmission and transaxles. When the throttle valve closes during the deceleration, The ECM shuts of fuel flow. This prevents and over-rich mixture during deceleration.
A rotary throttle position sensor is a variable resistor or potentiometer. It has a coil of resistance in the form of a half circle. One end connect to the ground and other end connect to a 5V source from the ECM. As the throttle valve position changes, the wiper blade moves along the coil. As the wiper slides, the voltage through the coil increases and correspondingly a voltage are sent to the ECM. The voltage tells the ECM the position of the throttle valve.

There are two types of fuel injectors to deliver fuel in to the air entering the engine. They are:-

1) Solenoid operated fuel injector
2) Mechanical fuel injector

The solenoid operated fuel injector is tuned on and off by the ECM. When the ignition key is on, voltage is present at the injector. The solenoid is energized when the ECM provides a ground. Then the injector opens and fuels sprays out. When the solenoid is de-energized, fuel spray stops.
In many engines, the injector delivers fuel in to an intake port that as only one intake valve. A single spray injector delivers a wide spray pattern through a single hole. A duel spray injector has two holes in the tip. The holes are positioned so the spray from each hole delivers fuel to one of the intake valve.


Figure: 3-2

The mechanical fuel injector is used in continuous injection systems. The injector is basically a fixed orifice with a mechanical needle valve operated by fuel pressure. The amount of the fuel injector dependence on the pressure applied to the fuel.


Figure: 3-3

Engines with electronic fuel injection have a cold start valve. It supplies extra fuel to satisfy a cold engine. The valve is similar to a solenoid operated fuel injector.
A thermo time switch limits the time the cold start valve can inject. This prevents the engine from receiving too much fuel or flooding. The thermo-time switch has a thermostatic blade, a pair of contacts and a heating element. When the engine cold, the blade is straight and the contacts are closed. ‘The cold start valve sprays fuel when the engine cranks. As the engine warms up, the thermostatic blade bends and the contacts separate. This opens


Figure: 3-4
The cold start valve is used to supply extra fuel for starting a cold engine.


Figure: 3-5
Thermo-Time switch limits how long the cold start valve can inject fuel

Sensors feed information into the ECM. The ECM then makes decisions and sends commands to various actuators. These are the device that operates automotive and engine components
Actuators are transducers that usually connect electrical signals from the ECM in to mechanical motion. Inputs are usually from sensors and switches. Outputs are usually sent to actuator, which then operates switches, valves and other devices.


The timing of the injection in an electronic port – injection system varies for different engines.
In some four and six cylinder engines, all fuel injectors open at the same time - once each crankshaft revolution. This arrangement is the simultaneous injection system. Each injector opens twice for each time its intake valve opens. The intervals between injection and intake valve opening are short that there are short that there is little loss in efficiency.
Some systems open half of the injections at the same time. This is group injection. Other systems open each injector separately in firing order sequence. This is sequential electronic fuel injection. It provides the most accurate fuel delivery and best engine performance while minimizing exhaust emissions.


Figure: 3-6


The major advantages of Digital Fuel Injection Systems are:-
1) The ECM can control all aspects of the combustion of the air-fuel ratio under all conditions
2) With the Digital Fuel Injection System the engine will be reliable, run smoothly, be more economical and have a longer lifespan.
3) The altitude and ambient temperature compensation ensure optimum performance at all altitudes, temperatures and seasons
4) The extremely accurate and optimal fuel delivery at any rpm and every load translates in to more horse power, better economy and less emission.
5) It don’t need constant tuning or adjustments.
6) The ECM can actually help prevent engine damage by not allowing full power and torque to be generated until or fluids are up to their normal operating temperature.


1) It is very experience and has pushed the prices of the vehicle.
2) It takes time to perform an effective conversion.
3) The local fuel quality is the biggest enemy of fuel injection. Adulteration and excessive gum content can play havoc, causing blockage of the pin hole small injectors.


Researches are going on and developments are made each day in the field of fuel injection systems. The digital fuel injection system has changed the complete concept of fuel injection and resulted in better efficient and powerful vehicles.



Automotive Mechanics : William H Cruise
Osnald L Anglin
Joseph Heitner

Internal Combustion Engines : Paul W Gill
James H Smith
Mathur & Sharma

Automotive Engines : William H Cruise
Donald L Anglin



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