Electronic Fuel Injection System

CONSTRUCTION OF GASOLINE FUEL INJECTION SYSTEM.

     There are many different gasoline fuel injection systems now being used on vehicles. Most systems are  of the four major types :

 1. Electronic control throttle body injection (TBI)

2 Electronic control port fuel injection (PFI)

 3 Mechanical control continuous injection systems (CIS)

4, Electronic control continuous injection systems (CIS-E)

   Most electronic fuel injection systems only inject fuel during part of the engine's combustion cycle. The engine fuel needs are measured by intake airflow past a sensor or by intake manifold pressure (vacuum). The airflow or manifold vacuum sensor converts its reading to an electrical signal and sends it to the engine control computer. The computer processes this signal (and others) and calculates the fuel needs of the engine. The computer then sends an electrical signal to the fuel injector or injectors. This signal determines the amount Of time the injector opens  and sprays fuel, This interval is known as the injector pulse width. Most domestic electronic fuel injection systems are either throttle bodys or port injection systems. Throttle body injection systems have a throttle body assembly mounted on  the intake manifold in the position usually occupied  by a carburettor. The throttle  body assembly usually contains one or two injectors.

      On port fuel injection systems, fuel injectors are mounted in the intake manifold runners. One injector is directed at the back of each intake valve, Aside from the differences in injector location  and number of injectors. operation of throttle  body and port systems is quite similar with regard to fuel and air metering, sensors and computer  operation. Continuous injection systems are used on Iow cost or previous Of vehicles. They deliver a ste.ady stream Of pressurized fuel into the intake manifold. In Other words. the injectors do not pulse  on and off as in pan and throttle body  systems. In CIS, the amount of fuel delivered is controlled by the rate of airflow entering the engine. An airflow sensor suspended in the path of the intake air controls movement Of a plunger that alters fuel flow to the injectors. Technically. CIS is a an-hank-ally controlled system. On early  the only electrical component was the high pressure fuel pump. Later CIS systems added oxygen sensor feedback circuits and other electronic controls.

 ELECTRONIC FUEL INJECTION SYSTEMS:

Electronic fuel  injection (EFT) is the most precise. reliable and most effective method of delivering fuel to the combustion chamber of the vehicles. EFT systems must provide the  correct air/fuel ration for all engine loads, speeds and temp.condition  To accomplish this,an EFI system use a fuel delivery  system ,load s, temperature conditions. To accomplish this ,an EFI system uses a fuel delivery system, air induction system, input sensor ,control computer, fuel injectors and an idle speed control.

THROTTLE BODY VERSUS PORT INJECTION :

 Fuel and air mixture within an EFI system depends on Whether a throttle body or ported design is used. However there are fuel system  components common to both  the systems. In a typical EFI fuel delivery system fuel is drawn from the fuel tank by an in-tank chassis-  mounted electric fuel pump. Before it reaches the injectors, the fuel passes through a filter that removes dirt and impurities. A fuel line pressure regulator maintains a constant fuel line pressure that may as high as 7 N/cm²in some systems. This fuel pressure generates the spraying force needed to inject the fuel. Excess fuel not required by the engine passes through the fuel pressure regulator and returns to the fuel tank through a fuel return line.

Throttte Body Fuel Injection.

For many auto manufacturers, throttle body injection (TBD served as a stepping stone from carburettors to more advanced port fuel injection systems. TBI units were used on many engines during the 1980s and are still used on some engines. The throttle body unit is similar in size and shape to a carburettor and like a carburettor. Mount on the intake manifold. Fuel supply and return line service  one or sometimes two fuel injectors. The injectors spray fuel down into a throttle body chamber leading to the intake manifold,

 PORT FUEL INJECTION (PFD)

This systems use one injector at each cylinder. They are mounted in the intake manifold near the cylinder head where they earl inject a fine, atomized fuel mist close as possible to the intake valve. Fuel lines run to each cylinder from a fuel manifold, usually referred to as a fuel rail. The fuel rail assembly on a PFI system of V-6 and V-8 engines usually consists of a left and right hand rail assembly. The two rails can connected either by crossover and return fuel tubes or by a mechanical bracket arrangement. Fuel tubes cross between the two rails and the pressure regulator attached to the back of one of the rails shows a fuel rail on a transverse four-cylinder engine, Since, each cylinder has its own injector, fuel distribution is exactly equal. With little or no fuel to wet the manifold walls, there is no need for manifold heat or an early fuel evaporation system. Fuel dœs not collect in puddles at the base of the manifold. This means that the intake manifold passages can be tuned or designed for &better low speed power availability. The port type systems provide a more accurate and efficient delivery of fuel. The throttle body in a port fuel injection system controls the amount of air that enters the engine as well as the amount of vacuum in the manifold. It also houses and controls the idle air control (LAC) motor and the throttle position sensor (TPS). The TPS enables the ECU to know where the throttle is Positioned  at all times.

       The throttle body is a single case aluminium housing with a single throttle blade attached to the throttle shaft. The TPS and the IAC valve/motor are also attached to the housing. The throttle shaft is Controlled by the accelerator pedal. The throttle shaft extends the full length of the housing. The throttle bore controls the amount of incoming air that enters the air induction system. A small amount Of coolant is also routed through a passage in the throttle body to prevent icing during cold weather. Port systems require an additional control system that throttle body injection units do not require. While throttle body injectors are mounted  above the throttle plates and are not affected by fluctuations in manifold vacuum, port system injectors have their tips located in the manifold where constant changes in vacuum would affect the amount of fuel injected.