How Harley-Davidson's EFI electronic injection works

Electronic injection systems are already part of our life on two wheels. They are more efficient as they produce more power with the same amount of fuel, pollute less and allow the engine to run more accurately.
We will explain in the simplest way possible the basic functioning of these increasingly advanced systems.

Injecting fuel
Electronic Fuel Injection (EFI) replaces the carburettor in its task of powering the engine with the fuel needed for its operation (in principle the engine is still the same and will develop the same raw power, it only changes how to feed it).
In an EFI system, 3 key parts are distinguished: the switchboard, the sensors and the actuators.

The switchboard
Also called ECM or ECU (Electronic Control Unit) is the brain of the system. This is a small computer, which communicates with the other components in an analogue way (by voltage) and also in digital mode, through a kind of "internet" that has the bike (for more details you can read this other article).

The function of the switchboard is to determine how much fuel and at what precise moment it must be injected into each cylinder. To do this it analyzes the information that comes from the different sensors (temperature, RPM, opening of the accelerator ...) and compares it with some tables or maps written in its memory. After calculating the quantity and the exact moment gives orders for the injectors to be opened allowing the passage of the gasoline to the cylinders. It also takes care of deciding when the spark should be emitted by the spark plug, controlling the ignition. All this several hundred times per second.

Sensors or inputs
The sensors are responsible for providing all the information needed by the ECU to know the conditions on which the vehicle is wheel (and its engine). The main ones are:

• CKP (Crankshaft Position) or crankshaft position sensor:

Located on the engine crankcase, the sensor distinguishes machined grooves in the crankshaft and determines the speed of rotation thereof, indicating to the centralite the speed of the engine or RPM.

• CMP (Camshaft Position) or position sensor of the camshaft.

Indicates in which phase the engine is found (admission, compression, explosion, or exhaust) through the reading of some marks in the camshaft.

• MAP (Manifold Air Pressure) or intake vacuum sensor.

It measures the depression in the intake manifold, indicating to the ECM the engine load and the air entering the cylinders.

• ET (Engine Temperature) or engine temperature sensor.

Located on the cylinder head, this sensor reports the grades to which the engine is operating, so the ECM knows whether the engine is cold or operating temperature.

• TPS (Throttle Position Sensor) or accelerator position sensor.

Through this input the switchboard knows how open the driver carries his accelerator fist. It is usually located near the intake butterfly.

• IAT (Intake Air Temperature) or intake air temperature sensor.

Reports the ambient temperature of the outside air through the meter located in the air inlet.

• O2 Sensor or Lambda probe.

Located in the exhaust, this sensor gives information about the quality of the combustion, allowing the ECM to know if the mixture is slightly "rich" or "poor" in real time.

• Knock Sensor or engine "chopped" sensor.

It is a tiny "microphone" attached to the engine block that offers to the centralità the ability to distinguish vibrations generated by a poorly adjusted advance, in real time, avoiding of this motorcycle catastrophic consequences for the internal components.

• Barometric sensor or barometric sensor

It indicates the atmospheric pressure and the variations in height, it is no longer necessary to adjust the carburetor if we move from the sea level to the plateau, or if the atmospheric conditions change.

This sensor tends to disappear in the last few years as the MAP sensor also performs this function, just before the bike is started.

The input cycle
To understand all these devices or inputs together, let us set an example:
We're rolling down a road at 90 KM per hour. The ECM knows we're going to 2060 RPM thanks to the crankshaft sensor signal. It also knows when the piston of each cylinder is in its upper dead point of admission by matching the RPMs with the current signal from the position sensor of the camshaft.
The ECM also knows that we roll "at the tip of the gas" through the throttle position sensor, and that we have a slight slope by checking the data of the MAP sensor, thus knowing the engine load. The engine is at operating temperature, indicating the voltage of the engine temperature probe.
With this data the centralite verifies the atmospheric pressure and the air temperature and compares all the information with the tables of the maps, in order to determine how much gasoline it is necessary to inject the engine at that moment and when to send the spark to the spark plug. Before you calculate it, you take into account the information from the Lambda probe to readjust your calculations.
Remember, all this happens on your bike hundreds of times per second while you feel the soft breeze on your face and decide to speed up a little more ...

System outputs
Once the information of the different sensors is received, the centralite or ECM compares all the data with which it has stored in its tables or maps and after processing the information it issues orders to the different control devices or outputs so that the engine works in the desired way.
These are the main Outputs of the system:

• IAC (Idle Air Control)

It is the "step by step" engine of idling control.

Open or close an air pass in the intake so that the engine is maintained to the programmed RPMs. Therefore, to lower the revolutions to idle you have to reschedule your table.

• Injectors

They provide the exact amount of gasoline to each cylinder at just the right time.

This amount is decided by the ECM and controls it by increasing or decreasing the time that they remain open.

• Ignition coil

The coil produces the spark individually for each cylinder at the exact moment.

In this way we can see that the ECM in addition to controlling the injection is also responsible for the advancement and adjustment of the ignition, automatically, using the information provided by the sensors.

• Active intake and exhaust systems

These valves open and close the air inlet in the filter and the outlet in the exhaust, they are used to be able to comply with the emission regulations.

If they are deactivated, they must be "told" to the ECM, programmatically.

• Throttle Control Actuator (TCA)

The Accelerator Control Engine handles the opening of the intake butterfly in the electronic accelerator systems.

In this case the throttle functions as a "scalextric" knob, sending a signal to the ECM, and it is this that is responsible for opening or closing the butterfly through the control motor.

Full control
Although it may seem complex, the truth is that with the adoption of the new injection control systems you can have access at the same time to ignition handling, emissions, braking and active safety... all without duplicate components and in a totally transparent way when it comes to performing system diagnostics, so its maintenance is simplified.

For example, with the help of ABS braking sensors the ECM (centralite) can detect if slippage occurs when accelerating and decide to activate a traction control system by simply modifying the TCA (accelerator) and Coil outputs (modifying ignition), without the need for additional parts.
Another advantage that can already be enjoyed with some switch units is the adoption of different maps (Economic, Sports, City, Wet...) and change the behavior of the vehicle immediately with the press of a button, resulting in a more manageable, less polluting and more fun bike.

Frank Burguera

#mecanicaharley