Multipoint - EFI System (Part1. FUEL INJECTION)

Fuel injection is a means of metering Fuel into an internal combustion engine. In modern automotive applications, fuel metering is one of several functions performed by an "engine management system". For gasoline engines, carburetors were the predominant method to meter fuel before the widespread use of fuel Injection. However, a wide variety of injection systems have existed since the earliest usage of the internal combustion engine. The primary functional difference between carburetors and fuel injection is that fuel injection atomizes the fuel by forcibly pumping it through a small nozzle under high pressure, while a carburetor relies on the vacuum created by intake air rushing through it to add the fuel to the air stream. The fuel injector is only a nozzle and a valve: the power to inject the fuel comes from further back in the fuel supply, from a pump or a pressure container.

A modern gasoline injection system, using pressure from an electric fuel pump, sprays fuel into the engine intake manifold. See Fig below. Like a carburetor, it pro­vides the correct air-fuel mixture for specific engine operating conditions. However, PRESSURE, not engine vacuum (suction), feeds the fuel into the engine cylinders. This makes gasoline injection very efficient.

Gasoline Injection Advantages

Gasoline injection has several advantages over a car­buretor. The most important of these are:
Improved atomization. Fuel is forced into the intake manifold under pressure. This helps break the fuel into a fine mist.
Better fuel distribution. Flow of fuel vapors to each cylinder is more uniform.
Smoother idle. A leaner fuel mixture can be used without rough idle because of better fuel distribution and low-speed atomization.

Simplified cutaway shows action of most common fuel injection system for a gasoline engine.

1. Improved fuel economy. Efficiency is high because of more precise fuel metering, atomization, and distribution.
2. Lower emissions. Lean, efficient air-fuel mixture reduces exhaust pollution.
3. Better cold weather operation. Injection gives bet­ter control of mixture enrichment than a carburetor choke.
4. More engine power. Precise metering of fuel to each cylinder and increased air flow can produce more horsepower.
5. Simpler. Late-model, electronic fuel injection systems have fewer parts than modern computer controlled carburetor systems.

Gasoline Injection Timing

The timing of a gasoline injection system relates engine valve action to the time when fuel is sprayed into the engine intake manifold. There are three basic classifications of gasoline injection timing: intermit­tent, timed, and continuous. An intermittent gasoline injection system opens and closes the injection valves independently of the engine intake valves. This type of injection system may spray fuel into the engine when the valves are open or when they are closed.
Another name for an intermittent injection system is MODULATED injection system. This is one of the most common types of gasoline injection. A timed injection system squirts fuel into the engine right before or as the intake valves open. It is timed to the opening of the engine intake valves. The best example of timed injection is a diesel injection system.
A continuous gasoline injection system sprays fuel into the intake manifold all of the time. Anytime the engine is running, some fuel is forced out of the injec­tor nozzles and into the engine.
The air-fuel ratio is controlled by increasing or decreasing fuel pressure at the injectors. This increases or decreases fuel flow Out of the injectors. A con­tinuous type injection system is frequently used on several foreign cars and on a few American cars.

Note four subsystems of an electronic gasoline injection system (dashed line boxes). Sensor systems feed data to computer. Computer uses this data to operate fuel delivery system. Parts of air system can a/so be controlled by computer.

Fuel Delivery System

The fuel delivery system cleans and meters the right amount of fuel for varied driving conditions. It is made up of an electric fuel pump, fuel filter, fuel rail, pressure regulator, injectors, and connecting lines and hoses.
The electric pump forces fuel out of the tank, through the lines, and into the pressure regulator. When the com­puter energizes the injectors, fuel sprays into the engine. Extra fuel bleeds out of the pressure regulator and back to the tank.
Note: Many of the parts (fuel pump, filters, lines, etc.)

Air Induction System

An air induction system for Electronic Fuel Injection provides clean air and delivers it to the engine cylinders. This system, typically, consists of an air filter, throttle body, throttle valve, intake manifold, and connecting air ducts.

Design of air induction systems will vary depending upon engine and fuel system design. However, they all have an air filter for removing airborne impurities, a throttle valve for controlling air flow into the engine, and other related parts.

Sensor System

The Electronic Fuel Injection sensor system keeps track of engine operating conditions and passes this information to the computer. See Fig below. A typical Electronic Fuel Injection sensor system includes an oxygen (exhaust gas) sensor, engine coolant tempera­ture sensor, air inlet temperature sensor, throttle posi­tion sensor, intake manifold pressure (vacuum) sensor, and other sensors.
Just as your body can sense a change in its surround­ings, (touching a hot stove for example), the sensor system can sense a change in the operation of many vehicle systems. It enables the modern fuel injection system to CHECK and CORRECT itself.

These diagrams summarize computer control system. A-Computer or ECU inputs. B -ECU (electronic control unit] outputs of various system parts. (Renault)

Computer Control System

The computer control system processes information and controls operation of the Electronic Fuel Injection system and certain other automobile systems.
A computer wiring harness carries current to and from the computer. Sensors from the engine, transmission, air conditioning system, and other systems send elec­trical information to the computer through the harness. Then, the computer can operate the injectors, transmis­sion, ignition system, emission control systems, and other components for maximum efficiency.