The Difference Between Carburettors and Fuel InjectionSeptember 25th, 2011 | Paul Sayer | Car Service

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In the last couple of decades, fuel injection systems have completely replaced carburettors as a means of delivering fuel into an engine in modern vehicles. In this article, we’ll take a look at how fuel injectors work and why they’ve become the industry standard. We’ll explain things as plainly as possible — remember, you don’t need to be a mechanic in order to gain a basic understanding of your vehicle’s inner workings!How does the carburettor work?Basically, the aim of the carburettor is to mix the appropriate amount of air and fuel in order to allow the engine to run properly. The carburettor is essentially a tube with an adjustable plate (known as the throttle plate) running across it. When the throttle plate runs parallel to the length of the tube, the maximum amount of air is flowing through the carburettors — this is known as full throttle. When the engine is idling, the throttle plate is just about closed, allowing minimal air to flow through.

The reason the carburettor went out of fashion was because it was an inefficient fuel delivery system. While these were fine on basic, old-fashioned automobiles (indeed, carburettors are still used on less complex machines such as chainsaws and lawnmowers even today), as cars evolved and became more complicated the carburettor was no longer efficient. Additionally, concern about fuel emissions in the atmosphere meant higher standards needed to be met by car manufacturers, and the fuel injector, which could more accurately deliver fuel to the engine, was the answer. The last carburettors were created in the late 1980s.

How does fuel injection work?Electronic fuel injection (EFI) is a computerised system that works by spraying fuel into the combustion chambers at regular intervals. When you put your foot on the accelerator, a throttle valve opens, allowing more air to enter the engine. The harder you push the accelerator, the more air gets in.

The engine control unit (ECU), which is the name for the computer that oversees the electronic parts of your engine, pays attention to how far the throttle valve has opened and allows more fuel to enter based on the amount of air that has made its way into the engine. Sensors will also work to monitor the mass of air in the engine, and also the levels of oxygen in the exhaust. By taking all this information into account, the ECU can create optimum air-to-fuel ratio. This is why EFI has become so important in modern car design.

What are the most common fuel injection problems?One of the most common fuel injection problems is a dirty injector. If these become clogged, this can lead to an engine misfiring. Some of the symptoms of clogged injectors include hesitation or stumbling during acceleration and general poor vehicle performance. Additionally, fuel injectors may leak fuel, resulting in higher fuel consumption. Using quality fuel ensures your fuel injectors don’t become clogged. If you do feel there may be a problem with your fuel injectors, it’s a good idea to get a professional car service to ensure that this is in fact the problems, as sometimes the symptoms could also be a result of something else being wrong with your vehicle.

How a Fuel Injection ECU (Engine Control Unit) System WorksJanuary 27, 2012

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 Email   A fuel injection ECU system is an important part of a fuel injected engine because it serves several functions aside from regulating and maintaining the amount of fuel and air that the engine needs to increase horsepower.

Electronic Fuel Injection SystemThe Electronic Control Unit is an integral part of the EFI or the Electronic Fuel Injection, which is a type of fuel injection system that is now commonly used among cars. EFI can be divided into 3 sub-systems: air induction system, fuel delivery system and the electronic control system.

The electronic control system of an EFI is where you will find the ECU. Aside from the ECU, this is also where you will find various sensors, fuel injector assemblies and any related fuel injection wiring.

Functions of a Fuel Injection ECU SystemA fuel injection ECU system has several functions. Probably one of the most important function of the ECU is it controls the fuel mixture used by the engine. The Engine Control Unit or ECU determines the amount of fuel that should be injected into engine. This computer program receives several data and computes them to come up with the appropriate amount. The ECU of an Electronic Fuel Injection also determines when is the right time to deliver the air and fuel ratio to the engine. This process is called injection duration or injection pulse width.

Most cars also have a built in control system in their ECU for idle speed. Idle speed is controlled through the programmable throttle stop. Aside from idle speed, an ECU controls the ignition timing of an engine. This is done by adjusting the time when the spark ignition plug should be sparked, resulting in better power.

The ECU system also controls the variable valve timing. This simply means that it controls when the valves will open. This is done to increase performance and power of the car since the flow of air into the cylinder is maximized.

Based on the data gathered by the ECU sensors, it can basically control the engine's speed, coolant temperature, throttle angle and exhaust oxygen content. 

System Operation of a Fuel Injection ECU System

A fuel injection ECU works by pulsing or controlling the fuel injectors in the engine. This is done by switching the injector ground circuit on or off depending on what is required by the engine. If the injector ground circuit is turned on the fuel is sprayed at the back of the intake valve.

When the fuel is sprayed, it mixes with the air. Due to the low pressures in the intake manifold, the fuel and air mixture then vaporizes. This is where the fuel injection ECU sensor works. It gives a signal to the ECU to provide the right air and fuel ratio. The ratio of air and fuel mixture is determined by the volume of air taken in by the engine and the engine's rpm. The sensors also provide the ECU with several other data including workload, exhaust gas composition as well as engine and ambient temperatures. All of these data gathered by the ECU sensor determines the amount of fuel needed to be injected and mixed with the incoming air.

Control of fuel injection: ECU will determine the quantity of fuel to inject based on a number of parameters. If the throttle pedal is pressed further down, this will open the throttle body and allow more air to be pulled into the engine. The ECU will inject more fuel according to how much air is passing into the engine. If the engine has not warmed up yet, more fuel will be injected .

Control of ignition timing : A spark ignition engine requires a spark to initiate combustion in the combustion chamber. An ECU can adjust the exact timing of the spark (called ignition timing) to provide better power and economy.

Control of idle speed : Most engine systems have idle speed control built into the ECU. The engine RPM is monitored by the crankshaft position sensor which plays a primary role in the engine timing functions for fuel injection, spark events, and valve timing. Idle speed is controlled by a programmable throttle stop or an idle air bypass control stepper motor.