MPFI

CONTENTS

INTRODUCTION 3

MAIN COMPONENTS OF MPFI4

AIR INTAKE SYSTEM 5 FUEL DELIVERY SYSTEM

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ELECTRONIC CONTROL SYSTEM8

WORKING OF MPFI11

SENSORS USED IN MPFI12

ADVANTAGES OF MPFI14

CONCLUSION 15

REFRENCES15

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MPFI

1. INTRODUCTION

Petrol vehicles uses device called carburetor for supplying the air

fuel mixture in correct ratio to cylinders in all rpm ranges. due to

construction of the carburetor is relatively simple, it has been used almost

exclusively on gasoline engines in the past. However in response to recent

demands for cleaner exhaust emission, more economical fuel consumption,

improved drivability, etc., the carburetor now must be equipped with

various compensating devices, making it more complex system.

So In place of the carburetor, therefore, the MPFI

(multi point fuel injection) system is used, assuring proper air fuel ratio to

the engine by electrically injecting fuel in accordance with various driving

conditions.

MPFI system injects fuel into individual cylinders, based on

commands from the ‘on board engine management system computer’ –

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popularly known as the Engine Control Unit/ECU. These techniques result

not only in better ‘power balance’ amongst the cylinders but also in higher

output from each one of them, along with faster throttle response. The

electronic fuel injection system supplies the combustion chambers with

air/fuel mixture of optimized ratio under widely varying driving

conditions.

2. MAIN COMPONENTS OF MPFI SYSTEM

This system has four major components they are:

a) Air intake system

b) Fuel delivery system

c) Electronic control system

2.1. Air intake system

. The air (corresponding to the throttle valve opening) is filtered by the air

cleaner, passes through the throttle body, and is distributed by the intake

manifold and finally drawn into each combustion chamber. When the lAC

valve is opened according to the signal from ECM, the air bypasses

the1hrottle valve through bypass passage and is finally drawn into the

intake manifold .

a. Throttle body

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. The throttle body consists of the main bore, air bypass passage and the

following parts. Throttle valve, which is interlocked with the accelerator

pedal and controls the amount of the intake air. TP sensor which detects

the throttle valve opening and sends a signal to ECM. lAC valve, which

supplies the bypass, air depending on Engine condition.

b. Idle air control valve

The lAC valve controls opening of the bypass air passage. The air bypasses

the throttle valve through bypass passage and is finally drawn into the

intake manifold. Opening and closing of the valve itself is determined by

operation of the magnet, which is connected to it. The magnet operates

according to electric current from ECM.

2.2. Fuel delivery system

The fuel in the fuel tank is pumped up by the fuel pump, filtered by fuel

filter and fed under pressure to each injector through the delivery 'pipe. As

the fuel pressure applied to the injector is always kept a certain amount

higher than the pressure in the intake manifold by the fuel pressure

regulator, the fuel is injected into the intake port of the cylinder head when

the injector opens according to the injection signal form ECM. The fuel

relieved by the fuel pressure regulator return through the fuel return to the

fuel tank.

a. Fuel pump

The electrical fuel pump located on the fuel tank consists of armature,

magnet, impeller, brush, check valve etc.The ECM controls its operation.

When the power is supplied to the fuel pump, the motor in the pump runs

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and so does the impeller. This causes a pressure difference to occur

between both sides of the impeller, as there are many grooves around it.

Then the fuel is drawn through the inlet port, and with its pressure

increases,

It is discharged through the outlet port, The fuel pump also has a check

valve to keep some pressure in the fuel feed line even when the fuel pump

is stopped.

b. Pressure regulator system

The fuel pressure regulator is diaphragm operated relief valve consisting of

diaphragm, spring and valve. It keeps the fuel pressure applied to the

injector 2.9Kglcm^2 higher than intake manifold at all times, The pressure

applied to the upper chamber of the fuel pressure regulator intake manifold

pressure and that to the lower chamber is fuel pressure. When the fuel

pressure rises more than 2,9Kg/cm2 higher than the intake manifold

pressure, the fuel pushes the valve in the regulator open and excess fuel

return to the fuel tank through return line.

c. Injector

Each cylinder has one injector. Which is installed between the intake

manifold delivery pipe. It is an electromagnetic type injection nozzle,

which injects fuel into the intake port of the cylinder head according to the

signal from ECM. When the solenoid coil of the injector is energised by

ECM, it becomes an Electro magnet and attracts the plunger. At the same

time, the ball valve which is incorporated with the plunger opens and the

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injector which is under the fuel pressure injects fuel. As the lift stroke of

the ball valve of the injector is set constant, the amount of fuel injected at

one time is determined by the length of the time during which the solenoid

is energized

2.3. Electronic control system

The electronic control system consist of various sensors which detect

the state of engine and driving conditions, ECM which controls various

devices according to the signals from the sensors and Various controlled

devices. The systems are

Fuel injection control system

Idle speed control system

Fuel pump control system,

Ignition control system,

Radiator fan control system,

Fuel injection control system

The electronic fuel injection system supplies the combustion chambers

with air/fuel mixture of optimized ratio under widely varying driving

conditions. It uses the sequential multi-port fuel injection system, which

injects fuel into each intake port of the cylinder head. In this system ECM

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controls the time and timing of the fuel injection from the fuel injector into

the cylinder head intake port according to the signals from the various

sensors so that suitable air/fuel mixture is supplied to the engine in each

driving condition. The factors to determine the injection time are the basic

injection time which is calculated on the basis of the engine speed and the

intake manifold pressure and various compensation which are determined

according to the signals from various sensors that detect the state of the

engine and driving conditions.

Idle speed control system

This system controls the bypass airflow by means of ECM & lAC valve for

the following purposes. To keep the engine idle speed as specified at all

times. The engine idle speed can vary due to load applied to engine, to

improve starting performance of the engine to compensate air fuel mixture

ratio when -decelerating, to improve drivability while engine is warmed

up. lAC valve operates according to duty signal sent from ECM. ECM

detects the engine condition by using the signals from various signals and

switches and controls the bypass airflow by changing lAC valve opening.

When the vehicle is at a stop, the throttle valve is at the idle position and

the engine is running, the engine speed is kept at a specified idle speed.

Fuel pump control system

ECM controls ON/OFF operation of the fuel pump by turning it ON, the

fuel pump relay under any of the conditions. For two seconds after ignition

switch ON. While cranking engine (while engine start signal is inputted to

ECM). While crankshaft position sensor or camshaft - position sensor

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signal is inputted to ECM.

Ignition control system

This system controls electronically the time of electric current flow to

ignition primary coil as well as ignition timing. ECM judges the engine

and vehicle conditions by using signals from various sensors, selects the

most suitable electric current flow time and ignition timing for that

engine and vehicle conditions from among those Prestored in its memory

and sends an ignition signal to the igniter in ignition coil assembly.

Controls of this system include three different types as follows. Ignition

timing control at engine start, ignition timing control after engine start,

electric current flow time control.

Radiator fan control system

This system controls operation (ON/OFF) of the radiator fan motor.

Radiator fan motor is turned ON and OFF by its relay when ECM controls.

Radiator fan motor turned ON at below 98°C and OFF at below 93°C

a. Engine Control Module (ECM)

ECM is installed to the underside of the instrument panel at the passenger's

seat side. ECM is a precision unit consisting of microcomputer,

analogue/digital converter input/output unit etc. It is an essential part of the

electronic control system for its functions include not only such a major

function as to control fuel injector, lAC valve, fuel pump relay, etc. But,

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also on-board diagnostic system (self-diagnosis function) and fail-safe

function.

WORKING OF MPFI.

b. On-Board diagnostic system

ECM diagnosis troubles which may occur in the area including the

following parts when the ignition switch is ON and the engine is running,

and indicates the result by turning on or flashing malfunction indicator

lamp (CHECK ENGINE LIGHT)

1. Oxygen sensor 2. Engine coolant temp sensor.3.TP sensor 4.

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IATsensor.5.MAP sensor

6.CMP sensor. 7. VS sensor. 8. CKP sensor. (MY 416).9 CPU of ECM.

ECM and malfunction indicator lamp (MIL) operate as follows

Malfunction indicator lamp lights when the ignition switch is turned ON

but engine at stop with the diagnosis switch terminal ungrounded

regardless of the condition of electronic fuel injection system. This is only

to check the malfunction indicator lamp bulb and its circuit.If the above

areas of electronic fuel injection system; is free from any trouble after the

engine start while engine is running. Malfunction indicator lamp turns

OFF. When ECM detects a trouble which has occurred in the above areas,

it makes malfunction indicator lamp turn ON while the engine is running

to warn the driver of such occurrence of trouble and at the same time is

stores the trouble area in ECM back-up memory. The memory is kept as it

is even if the trouble was only temporary and disappeared immediately.

And it is not erased unless the power to ECM is shut off for specified time

60 sec. or longer. ECM also indicates trouble area in memory by means of

flashing of malfunction indicator lamp at the time of inspection.

. Fail- safe function

Even when a trouble has occurred in such area of electronic fuel

injection system that includes the following parts and a failure signal is

sent to ECM. control over the injector, idle air control valve and others is

maintained on the basis of the standard signals and/or CPU. This function

is called failsafe function. Thus with this function a certain level of engine

performance is available even when some failure occurs in such area and

disability in running is avoided.

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4. SENSORS USED IN MPFI.

1 Manifold absolute pressure (MAP) sensor

This sensor senses pressure change in the intake manifold and converts it

into voltage Change. It consists of a semi-conductor type pressure

converting element, which converts a pressure change into an electrical

change and, an electronic circuit which amplifies and corrects the electric

change. The ECM sends a 5-volt reference voltage to the pressure sensor.

As the manifold pressure changes, the electrical resistance of the sensor

also changes By monitoring the sensor output voltage ,ECM knows the

manifold pressure, ECM uses the voltage signal from the pressure sensor

as one of the signals to control fuel injector.

2. Throttle position sensor

The throttle position sensor is connected to the throttle valve shaft on the

throttle body, and detects throttle valve opening, the throttle opening is

detected by the potentiometer. A 5-volt reference Voltage is applied to the

sensor from ECM and as Brush moves over the print resistance according

to the throttle valve opening, the output voltage varies accordingly. By

monitoring sensor output voltage, ECM detects the throttle valve opening.

ECM uses the signal from TP sensor as one of the signals to control

various devices.

3 Intake air temperature sensor

Located on the air cleaner outlet hose, this sensor constantly measures the

Temperature of the air entering there and converts a change in the air

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temperature

Into that in resistance through its thermistor. That is, as is temperature

lowers, resistance increases and as it rises, resistance decreases. As air

density of the intake air varies with Variation in temperature, ECM, by

monitoring the resistance, adjusts the amount of fuel injection according to

the air temperature

4 Engine coolant temperature sensor

Incorporated with coolant temperature. Gauge and installed to

thermostat case, this sensor measures the temperature of the engine coolant

and converts its change into that in resistance through the thermistor like

the air temperature sensor, by monitoring the resistance of the coolant

temperature sensor, ECM detects the engine coolant temperature and that

affects most systems under the control of ECM.

5 Oxygen sensor

The oxygen sensor is installed on the exhaust manifold to detect the

concentration of oxygen in the exhaust gases. in order of engines equipped

with the three- way catalytic converter to achieve their best exhaust

emission purification performance, it is necessary for the air-fuel ratio to

be kept within a narrow range near the theoretical air-fuel ratio The

oxygen sensor senses whether the air-fuel ratio is richer on leaner than the

theoretical air-fuel ratio, The oxygen sensor is located in the exhaust

manifold and consists of an element made of zirconium dioxide (zrO2, a

kind of ceramic material) This element is coated on both inside and outside

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with a thin layer of platinum. Atmospheric air is introduced into the inside

of the sensor, and outside of the sensor is exposed to the exhaust gases. If

the Oxygen concentration on the inside surface of the zirconium element

differs greatly from that on the outside surface at high temperatures, the

zirconium element generate a voltage when the air-fuel mixture is lean

there is lot of oxygen in the exhaust gas, so there is a little difference

between oxygen concentration inside and outside the sensor element. Thus

the voltage generated by the zirconium element is low if the air-fuel

mixture is rich; the oxygen in the exhaust has almost disappears. This

creates a large difference in the oxygen concentrations inside and outside

the sensor and voltage generated by the zirconium element is large. The

ECM uses this signal to increase or reduce the injection volume to keep the

air-fuel ratio at an even value near the stoichiometric air-fuel ratio.

6 Vehicle speed sensor

The vehicle speed sensor, located on the transmission gearbox or

speedometer, Generates a signal in proportion to the vehicle speed.

Receiving this signal, the speedometer uses it for operation of its indicator

and also converts it into to the ON/OFF signal by doubling the cycle. This

signal is sent to ECM where it is used as one of the signals to control

various devices.

7. Camshaft position sensor

The sensor is mounted on the sensor case (distributor less ignition case) on

tile camshaft let side for distributor less ignition vehicle and other vehicles

on the distributor. The signal rotor is press-fitted onto the camshaft

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(distributor less ignition vehicle) and other vehicles on the distributor shaft.

As the sensor has a built-in hall element and a waveform forming circuit, it

converts changes in the magnetic flux caused by rotation of the signal rotor

into electric pulse signals, Using this signal and the signal from the CKP

sensor (if equipped), ECM identifies the cylinder whose piston is in the

compression stroke.

8. Crank shaft position sensor

The sensor consists of magnet and coil. It is mounted on oil pan with

specified air gap between the sensor core end and crankshaft timing belt

pulley tooth. As the crankshaft turns, AC voltage is generated in the

sensor. ECM uses this signal as: Engine speed, Cylinder identification.

5. ADVANTAGES OF MPFI

1) More uniform A/F mixture will be supplied to each cylinder; hence the

difference in power developed in each cylinder is minimum. Vibration

from the engine equipped with this system is less, due to this the life of

engine components is improved.

(2) No need to crank the engine twice or thrice in case of cold starting as

happens in the carburetor system.

(3) Immediate response, in case of sudden acceleration / deceleration.

(4) Since the engine is controlled by ECM* (Engine Control Module),

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more accurate amount of A/F mixture will be supplied and as a result

complete combustion will take place. This leads to effective utilization of

fuel supplied and hence low emission level.

(5) The mileage of the vehicle will be improved.

6. CONCLUSION

Almost all vehicles in India are changing to the mpfi because of law

emissions, improved mileage and drivability since the engine is

controlled by micro computer more accurate amount of a/f mixture will

be supplied and as a result complete combustion will take place. this

leads to effective utilization of fuel supplied and hence low emission

level. it reduces wastage of fuel by the use of sensors and other control

systems

7. REFERENCES

Automotive technology –Jack

erjavec

Automobile engineering – Anil

chhakra

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Automobile engineering-V.Ganesh

www.howstuffworks .com

www.indiacar.com

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