Sylvie Willis
The primary function of electronic fuel injectors is to supply the correct amount of fuel to the engine so that it can combust effectively and power the engine. Electronic fuel injectors have been the primary means of getting gasoline into the engine cylinder since the 1990s. The injector is located in the combustion chamber, inlet manifold, or throttle body. The fuel injector is a valve controlled by springs or an ECU (Electronic Control Unit) and is capable of opening and closing several times per second. The ECU calculates the specific amount of fuel that needs to enter the cylinders and controls the ignition timing and various other engine functions.
| Characteristics | Values |
|---|---|
| Purpose | Supply the correct amount of fuel to the engine so it can combust it in an effective way to power the engine |
| Components | Fuel injectors, fuel pump, engine control unit (ECU), throttle valve, fuel rail, injector valves, injection valves, unit injectors |
| Function | Fuel injectors spray fuel into the engine, controlled by the ECU |
| Control | The ECU calculates the amount of fuel to be injected based on various factors such as air temperature, air intake pressure, engine speed, accelerator position, etc. |
| Types | Continuous injection, timed injection (pulsed injection), mechanical injection, electronic fuel injection (EFI) |
| Advantages | More accurate fuel metering, quicker response, improved fuel economy, better performance, reduced emissions |
| History | First appeared in the 1950s; widely used in European cars since around 1980; now standard in all cars sold in the US |
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What You'll Learn
The role of the engine control unit (ECU)
The engine control unit (ECU) is a device that controls various subsystems of an internal combustion engine. The ECU, also called an engine control module (ECM), plays a crucial role in the operation of electronic fuel injectors.
One of the primary functions of the ECU is to control the injection of fuel into the engine. It determines when the injectors should be activated and how much fuel should be injected. The ECU ensures that the right quantity of the fuel/air mixture is supplied to the engine according to its wide range of demands. This is achieved by monitoring the throttle valve position and adjusting the fuel rate accordingly. When the throttle valve opens, the ECU increases the fuel rate in anticipation of more air entering the engine.
The ECU also controls the timing of the spark to ignite the fuel in petrol engines. It uses a Crankshaft Position Sensor to determine the position of the engine's internals, ensuring that the injectors and ignition system are activated at precisely the right time. This precise control allows for optimal engine performance and efficiency.
In addition to fuel injection and ignition timing, the ECU is responsible for managing various other engine functions. For example, it controls the idle speed and variable valve timing or lift systems. The ECU uses digitally stored equations and numeric lookup tables to make these calculations and adjustments.
The introduction of the ECU has brought significant advancements to fuel injection systems. It has replaced the manual and often inaccurate methods of managing fuel and ignition, such as the choke' on the carburetor, with precise electronic control. This has led to improved engine performance, fuel efficiency, and emissions control.
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Injector location
To locate the fuel injectors in your vehicle, you can start by identifying the intake manifold. It is usually located behind or above the engine and consists of 4-8 pipes leading into the engine. The fuel injectors are the connectors that run from the fuel rail into these pipes. The fuel rail is a pipe that supplies pressurized fuel to all the injectors, ensuring that each cylinder receives an equal amount of fuel.
When replacing or servicing fuel injectors, it is important to refer to the vehicle's manual for specific instructions. The process may involve unlocking the fuel rail using tools like socket wrenches or screwdrivers and gently removing the injectors from their slots. It is recommended to take a reference photo of the injector orientation before making any adjustments. Additionally, dipping the tip of new injectors in gasoline can help lubricate the O-rings and prevent fuel leakage.
The location of the injectors can also vary depending on the type of injection system. In manifold injection systems, the injectors are located at the intake ports or throttle body, while in direct injection systems, the fuel is injected directly into the main combustion chamber of each cylinder. This allows for a more precise mixture of air and fuel, resulting in improved combustion and fuel efficiency.
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Injector types
Fuel injectors are electronically controlled valves. They are supplied with pressurised fuel by the fuel pump in a car. When the injector is energised, an electromagnet moves a plunger that opens the valve, allowing the pressurised fuel to squirt out through a tiny nozzle. The nozzle is designed to atomise the fuel, creating a fine mist that can burn easily. The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open, which is called the pulse width.
There are several types of fuel injectors, which can be broadly categorised into four main types:
- Single-point fuel injection: This is the simplest and oldest form of fuel injection. It replaces the carburettor with one or two fuel-injector nozzles in the throttle body, which is the throat of the engine's air intake manifold. This type of injection is also called throttle body injection (TBI).
- Multi-point fuel injection: This type of injection devotes a separate injector nozzle to each cylinder, right outside its intake port. This is why the system is sometimes called port injection. Every injector sprays fuel at the same time, and each cylinder gets a more precise volume of fuel, with less possibility of fuel condensation outside the intake manifold.
- Sequential fuel injection: This type of injection triggers each injector nozzle independently. The injectors spray fuel immediately before or as their intake valve opens. Sequential injection is the most common and effective system currently in use.
- Direct fuel injection: In this system, the injector is placed inside the cylinder to directly inject the fuel, bypassing the intake valve or manifold. Direct injection is more common in diesel engines but is also used in petrol engines, where it is known as GDI (gasoline direct injection).
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Fuel pressure
The role of the fuel injector is to supply the correct amount of fuel to the engine so it can be effectively combusted to power the engine. The engine requires an exact amount of fuel and air for combustion, and too much or too little fuel can cause the engine to choke or not start. The fuel injector is a valve that can open and close several times per second. The amount of time the fuel injector stays open is called the pulse width and is controlled by the ECU. The pulse width is determined by the amount of air entering the engine, which is regulated by the throttle valve.
The ECU calculates the specific amount of fuel that needs to enter the cylinders based on real-time data from sensors that track air temperature, air intake pressure, engine temperature, engine speed, and accelerator position. The fuel is then divided into several cylinders and sprayed into the combustion chamber.
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Fuel metering
The ECU also controls the ignition timing and other engine functions. When the injector is energized, an electromagnet moves a plunger that opens the valve, allowing pressurized fuel to squirt out through a tiny nozzle. The nozzle atomizes the fuel, creating a fine mist that can burn easily. Mechanical systems, which use a spring-loaded injector, have largely been superseded by electronic fuel injection systems due to their increasing reliability and decreasing costs.
The two main types of control for multi-port systems are simultaneous opening of all injectors or sequential multi-port fuel injection, where each injector opens just before the intake valve for its cylinder. Sequential fuel injection offers quicker response times and more precise fuel control, leading to better fuel economy, performance, and emissions. The pulse width for a given operating condition is determined by the ECU using a formula and lookup tables.
The fuel injector is located in the combustion chamber, inlet manifold, or throttle body. Injectors that control the metering are called injection valves, while those that perform all three functions (metering, ignition timing, and other engine functions) are called unit injectors. The fuel is delivered from the metering unit to each injector, which then sprays the fuel into the inlet port in the cylinder head. The injector contains a spring-loaded valve that opens when the fuel is squirted in, and the amount of fuel sprayed is controlled by a mechanical or electrical unit.
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Frequently asked questions
The purpose of an electronic fuel injector is to supply the correct amount of fuel to the engine so that it can be effectively combusted to power the engine.
An electronic fuel injector is a valve that is controlled electronically. The injector is connected to the throttle valve, which regulates how much air enters the engine. When the gas pedal is pressed, the throttle valve opens up, letting in more air. The engine control unit (ECU) then increases the fuel rate to match the amount of air entering the engine. The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open, which is called the pulse width.
Fuel injection has been around since the 1950s, and electronic fuel injectors were widely used on European cars starting around 1980. Initially, electronic fuel injectors used analogue electronics for the control system. Now, all cars sold in the United States have electronic fuel injection systems, and all production EFI systems are fully electronic with computer controls and electronic injectors.
