ELECTRONIC FUEL INJECTION
Introduction
Strict emission standards require precise fuel delivery
Computers used to calculate fuel needs
EFI very precise, reliable & cost effective
EFI provide correct A/F ratio for all loads, speeds, & temp ranges
The Fuel Injector
Electromechanical device
Controlled by PCM
Engine rpm determines when injector opens
How long it stays open determined by:
Engine temp
Engine load
Throttle pos.
O2 sensor voltage
Throttle Body Injection (TBI)
First injection unit used
Housing similar to Carb
One or two injector
One or two of these units mounted to intake manifold
LOW PRESSURE FUEL INJECTOR
13-16 psi operating pressure
Ball style pintle
Easily replaceable
Multi-Port Fuel Injection
One injector per cylinder
Mounts in intake manifold, sprays directly at intake valve
Fired in groups or individually (SFI)
Ram Tuning for denser air charge
Lower A/F temps
Leaner mixture during warm-up
Fuel Pressure Regulator
Located at end of fuel rail
Maintains constant pressure at injectors
Internal chamber contains a diaphragm
Pressurized fuel on one side
Manifold vacuum & spring tension on other
Manifold vacuum pulls up on diaphragm, metering fuel that is returned to tank
Excess fuel pressure can overcome spring tension, allowing fuel to return to tank
Increases in manifold pressure causes spring tension to push diaphragm down, blocking return line, increasing pressure in rail.
Central Port Injection (CPI)
Injector located in center of intake manifold
60 psi system
6 or 8 poppet valves attached to one TBI type injector
Central Multi-Port Injection (CMPI)
Similar to CPI
Individual injectors, with poppet valves

Fuel Injection

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INTRODUCTION:

Fuel Injection is the alternative method of supplying the engine with its working charge of fuel. The pressurization of fuel leads to improved automization which is considered to be good for performance.
Although, the modern carburettor is cheep and reliable, it has number of inherent disadvantages that make the supply of correct A: F mixture at all times difficult. The problem is further accentuated when a single carburettor has to supply the mixture to multicylinder engine. In addition to this, the throat restricts the flow of air to the engine. The maximum power can be increased by using a large throat by this affect the economy of fuel. Multiple carburettors assist the distribution problem but it also increases fuel consumption due to low air velocity at low engine speed and capital cost.
For these reasons, many attempts have been made to design a satisfactory Petrol Injection system. In which, each cylinder is supplied with its correct quantity of petrol for each working cycle under all operating conditions.



ELECTRONIC FUEL INJECTION SYSTEM (EFI) FOR PASSENGIER CARS


In the case of carburettor, the entire working is depends on the throttle position and all the system must be tailored so that proper mixture delivery takes place at every throttle position. The fuel delivered to engine by carburettor cannot easily be adjusted to suit certain important operating conditions of the engine such as water temperature, oil temperature, air temperature etc. to level of precision called for with stringent emission control requirements. In the case of fuel injection, this is achieved by Electronic means. It is possible to make the system recognized and respond to every operating condition of the engine and to deliver the required mixture at all operating conditions.


SYSTEM DISCRIPTION:

There are two types of fuel injection systems, namely Single Point Injection (SPI) and Multi Point Fuel Injection (MPFI) systems. Both systems are low pressure injection systems with pump pressure of 3 to 4 bar. In the SPI system, which is also called throttle body injection system, fuel delivery takes place at one point adjacent to the throttle. The Electronic Control Unit (ECU) senses many engine parameters including measurement of air flow and oxygen content in the exhaust so that the fuel is delivered in the right quantity at all operating points.