Yahoo Autos How Electronic Fuel Injection Works
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New cars are confusing — intimidating even. With all the computers, sensors, and gadgets, and now, even hybrid technology, it may seem like there’s some sort of magical witchcraft taking place under the hood. We’re here to lessen the mystery and show you how modern automotive computer control systems work. Today, we’re talking electronic fuel injection.
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How Does Variable Valve Timing Work?
Back in the day, a good ol’ carburetor was responsible for sending the appropriate amount of fuel into the cylinders. Today, that job belongs to the Engine Control Unit (ECU). But how does that computer get the information and fuel to the engine the same way a mechanical carburetor would?
For a lot of you this is review, but if we want a new generation of car enthusiasts to care about cars, it can’t hurt to explain how they actually work.
The Basics of Electronic Fuel Injection
If the heart of a car is its engine, then its brain must be the ECU. Also known as a Powertrain Control Module (PCM), the ECU optimizes engine performance by using sensors to decide how to control certain actuators in an engine.
A car’s ECU is primarily responsible for four tasks. First, the ECU controls the fuel mixture. Second, the ECU controls idle speed. Third, the ECU is responsible for ignition timing. And lastly, in some applications, the ECU controls valve timing.
Before we talk about how the ECU accomplishes its tasks, let’s follow the path of a gasoline droplet that enters your gas tank. Times have changed since the Down the Gasoline Trail video, so it’s time for an update.
Initially, after a gas droplet enters your gas tank (which is now made of plastic), it gets sucked up by an electric fuel pump. The electric fuel pump usually comes in an in-tank module that consists of a pump, a filter, and a sending unit. The sending unit uses a voltage divider to tell your gas gauge how much fuel you have left in your tank. The pump sends the gasoline through a fuel filter, through hard fuel lines, and into a fuel rail.
How Electronic Throttle Control Works
A vacuum-powered fuel pressure regulator at the end of the fuel rail ensures that the fuel pressure in the rail remains constant relative to the intake pressure. For a gasoline engine, fuel pressure is usually on the order of 35-50 psi. Fuel injectors connect to the rail, but their valves remain closed until the ECU decides to send fuel into the cylinders.
Usually, the injectors have two pins. One pin is connected to the battery through the ignition relay and the other pin goes to the ECU. The ECU sends a pulsing ground to the injector, which closes the circuit, providing the injector’s solenoid with current. The magnet on top of the plunger is attracted to the solenoid’s magnetic field, opening the valve. Since there is high pressure in the rail, opening the valve sends fuel at a high velocity through the injector’s spray tip. The duration that the valve is open and consequently the amount of fuel sent into the cylinder depends on the pulse width (i.e. how long the ECU sends the ground signal to the injector.)
When the plunger rises, it opens a valve and the injector sends fuel through the spray tip and into either the intake manifold, just upstream of the intake valve, or directly into the cylinder. The former system is called multiport fuel injection and the latter is direct injection.
Controlling Fuel Mixture
We’ve already looked at how electronic throttle control works. We showed you that, when a driver pushes his or her gas pedal, an accelerator pedal position sensor (APP) sends a signal to the ECU, which then commands the throttle to open. The ECU takes information from the throttle position sensor and APP until the throttle has reached the desired position set by the driver. But what happens next?
