How the EFI electronic injection of Harley-Davidson works

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

Injecting fuel
Electronic injection or EFI (Electronic Fuel Injection) replaces the carburetor in its mission of feeding the engine with the necessary fuel for its operation (in principle the engine remains the same and will develop the same gross power, only change the way to feed it) .
In an EFI system, 3 fundamental 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. It is a small computer, which communicates with the other components in an analog (by voltage) and also digitally, through a kind of “internet” that has the motorcycle (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, analyze the information that comes from the different sensors (temperature, rpm, opening of the accelerator ...) and compares it with tables or maps written in your memory. After calculating the amount and the exact moment it gives orders to open the injectors allowing the passage of gasoline to the cylinders. It is also responsible for deciding when the spark plugs should emit, controlling the ignition. All this several hundred times per second.

Sensors or inputs
The sensors are responsible for facilitating all the information that ECU needs to know the conditions in which the vehicle (and its engine) rolls. The main ones are:

• CKP (crankshaft position) or crankshaft position sensor:

Located in the engine crankcase, the sensor distinguishes some mechanized grooves in the crankshaft and determines the rotation speed of the same, indicating the engine speed or rpm to the switchboard.

• CMP (camshaft position) or camshaft sensor.

Indicates in which phase is the engine (admission, compression, explosion or escape) through the reading of brands in the camshaft.

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

It measures depression in the admission multiple, indicating to the ECM the load of the engine and the air that enters the cylinders.

• ET (Engine Temperature) or engine temperature sensor.

Located in the butt or cylinder, this sensor informs of the degrees to which the engine is working, thus the ECM knows if the engine is cold or at operational temperature.

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

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

• IAT (INTAKE Air Temperature) or Admission Air Temperature Sensor.

Informs the ambient temperature of the outer air through the meter located at the air inlet.

• O2 sensor or Lambda probe.

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

• Knock sensor or motor "chopped" sensor.

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

• Barometric sensor or sensor

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

This sensor tends to disappear in recent years since the MAP sensor also performs this function, just before starting the motorcycle.

The entry cycle
To understand all these devices or inputs together, we will give an example:
We are rolling along a 90 km road per hour. The ECM knows that we are going to 2060 rpm thanks to the crankshaft sensor signal. He also knows when the piston of each cylinder is in its upper dead point of admission, collating the RPM with the signal of the camshaft position sensor.
The ECM also knows that we shot “at a gas tip” through the accelerator position sensor, and that we upload a light slope checking the MAP sensor data, thus knowing the engine load. The engine is at operational temperature, indicates the motor temperature probe voltage.
With these data the switchboard verifies the atmospheric pressure and the air temperature and compares all the information with the maps tables, to determine how much gasoline it is necessary to inject the engine at that same time and when to send the spark to the spark plug. Before calculating it, it takes into account the information of the Lambda probe to readjust its calculations.
Remember, all this happens on your motorcycle hundreds of times per second while you feel the soft breeze on the face and decide to accelerate a little more ...

System outputs
Once the information from the different sensors is received, the switchboard or ECM compares all these data with which you have stored in your tables or maps and after processing the information emits orders to the different control devices or exits so that the engine works in the way desired
These are the main outputs of the system:

• IAC (idle air control)

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

Open or close an air step in the admission so that the engine is kept at programmed RPMs. Therefore, to lower the Revolutions to idle you have to reprogram your table.

• Injectors

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

This amount is decided by the ECM and controls it by increasing or decreasing the time 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 progress and adjustment of the ignition, using the information provided by the sensors.

• Active admission and escape systems

These valves open and close air entry into the filter and exhaust in the exhaust, are used to comply with emission regulations.

If they are deactivated, you have to “tell it” to the ECM, by programming.

• TCA (Throttle Control Actuator)

The accelerator control engine is responsible for opening the admission butterfly in electronic accelerator systems.

In this case, the accelerator works as a “Scalextric” command, sending a signal to the ECM, and it is the one that is responsible for opening or closing the butterfly through the control engine.

Total control
Although it seems complex, the truth is that with the adoption of the new injection control systems, it can be accessed at the same time to the management of the ignition, to the emissions, to the braking and safety active ... everything without duplicity of components and in a totally transparent way when making system diagnoses, so its maintenance is simplified.

For example, with the help of the ABS braking sensors, ECM (switchboard) can detect if sliding when accelerating and deciding to activate a traction control system simply by modifying the outputs of the TCA (accelerator) and the coil (modifying the ignition) , without the need for additional pieces.
Another advantage that can already be enjoyed with some switches is the adoption of different maps (economic, sports, city, wet ...) and change the behavior of the vehicle immediately with the pulsation of a button, which obtains a Most manageable, less polluting and more fun motorcycle.

Frank Burguera

#mecanicaharley