How a Fuel Injection ECU (Engine Control Unit) System Works

January 27, 2012

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 System

The 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 System

A 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.

Related Questions and Answers

What ECU Types are Available for Cars?

There are five main ECU types in use in automobiles these days. The ECU is the Electronic Control Unit, sometimes referred to as the Engine Management System (EMS). This is the brain that controls the engine, telling the injectors how long to stay open, injecting fuel and telling the coil when to send the spark to the plugs to ignite the fuel air mixture. The five basic types are Pre-OBD, OBD-0, OBD-O VTEC, OBD-1 and OBD-2. These different types of control units can be identified by the connector design, and by using the part numbers on the computer case. 

How Often should You Clean Car Fuel Injectors?

Clean car fuel injectors deliver a number of benefits. The most important benefit they deliver these days is more efficient use of the fuel, since the fuel is atomized much better by a clean injector. Allowing it to more completely mix with the incoming air charge. All other benefits can be attributed to this single fact. Clean injectors allow your engine to make better power, requiring less throttle pressure for a given speed. Manufacturers recommend that you clean your injectors on a yearly basis or every 12,000 miles. IF you use a high quality detergent fuel, such as those from Chevron, you can push that to every 18 months, though.

What is the Ideal ECU Idle Speed?

ECU idle speed is the speed that your engine runs at when you have you have your foot completely off the accelerator pedal. This is an important setting for properly tuning a vehicle with an adjustable distributor, since idle speed affects the engine timing greatly. Optimal idle speed will normally depend mostly on what type of transmission your car has. Most cars with an automatic transmission should idle at seven hundred RPM, at operating temperature and the transmission in Park. Cars equipped with a manual transmission should be set to idle slightly higher in neutral, around 800 RPM.