How Harley-Davidson's EFI Works

Electronic fuel injection systems are now a common part of our lives on two wheels. They are more efficient, producing more power with the same amount of fuel, polluting less, and allowing the engine to operate more precisely.
We are going to explain in the simplest possible way the basic operation of these increasingly advanced systems.

Injecting fuel
Electronic fuel injection (EFI) replaces the carburetor in its role of supplying the engine with the fuel necessary for its operation (in principle the engine remains the same and will develop the same gross power, only the way it is supplied changes).
In an EFI system, there are three fundamental parts: the control unit, the sensors, and the actuators.

The switchboard
Also called the ECM or ECU (Electronic Control Unit), it's the brain of the system. It's a small computer that communicates with the other components both analogously (via voltage) and digitally, via a kind of "internet" within the motorcycle (for more details, you can read this other article ).

The function of the ECU is to determine how much fuel should be injected into each cylinder and at what precise moment. To do this, it analyzes the information received from various sensors (temperature, RPM, throttle opening, etc.) and compares it with tables or maps stored in its memory. After calculating the quantity and the exact moment, it commands the injectors to open, allowing gasoline to flow into the cylinders. It also decides when the spark plugs should ignite, controlling the ignition. All of this occurs several hundred times per second.

Sensors or inputs
The sensors are responsible for providing all the information the ECU needs to know the operating conditions of the vehicle (and its engine). The main ones are:

• CKP (Crankshaft Position) or crankshaft position sensor:

Located in the engine crankcase, the sensor detects grooves machined into the crankshaft and determines its rotation speed, indicating the engine speed or RPM to the control unit.

• CMP (Camshaft Position) or camshaft position sensor.

It indicates the engine's current phase (intake, compression, combustion, or exhaust) by reading marks on 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 in the cylinder head, this sensor reports the engine's operating temperature, allowing the ECM to know whether the engine is cold or at operating temperature.

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

Through this input, the ECU knows how far the driver has their throttle grip open. It's usually located near the throttle valve.

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

It reports the ambient temperature of the outside air through the meter located at the air inlet.

• O2 Sensor or Lambda Probe.

Located in the exhaust, this sensor provides information on combustion quality, allowing the ECM to know whether the mixture is slightly “rich” or “lean” in real time.

• Knock Sensor or engine “knock” sensor.

It's a tiny "microphone" attached to the engine block that allows the ECU to detect vibrations generated by improperly adjusted timing in real time, thus preventing catastrophic consequences for internal components.

• Baro sensor or barometric sensor

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

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

The input cycle
To understand all these devices or inputs together, let's give an example:
We're traveling down a highway at 90 km/h. The ECM knows we're traveling at 2060 RPM thanks to the signal from the crankshaft sensor. It also knows when each cylinder's piston is at its top dead center by comparing the RPM with the signal from the camshaft position sensor.
The ECM also detects that we're driving "full throttle" via the throttle position sensor and that we're climbing a slight hill by checking the MAP sensor data, thereby determining the engine load. The engine is at operating temperature, as indicated by the voltage from the engine temperature sensor.
Using this data, the ECU checks atmospheric pressure and air temperature and compares all the information with the mapping tables to determine how much fuel needs to be injected into the engine at that moment and when to deliver the spark to the spark plug. Before calculating this, it takes into account the information from the Lambda probe to readjust its calculations.
Remember, all of this happens on your bike hundreds of times per second while you feel the gentle breeze on your face and decide to accelerate a little more...

System outputs
Once the information from the different sensors is received, the control unit or ECM compares all this data with what it has stored in its tables or maps and, after processing the information, issues orders to the different control devices or outputs so that the engine operates as desired.
These are the main outputs of the system:

• IAC (Idle Air Control)

It is the idle control “stepper” motor.

It opens or closes an air passage in the intake to maintain the engine's programmed RPM. Therefore, to lower idle speeds, you must reprogram your engine speed control.

• Injectors

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

This amount is decided by the ECM and controlled 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, also automatically controls the timing and adjustment of the ignition, using the information provided by the sensors.

• Active intake and exhaust systems

These valves open and close the air inlet to the filter and the outlet to the exhaust, and are used to comply with emissions regulations.

If they are deactivated, the ECM must be “told” through programming.

• TCA (Throttle Control Actuator)

The Throttle Control Motor is responsible for opening the intake throttle valve in systems with electronic throttle.

In this case, the accelerator works like a "scalextric" control, sending a signal to the ECM, which is responsible for opening or closing the throttle valve through the control motor.

Total control
Although it may seem complex, the truth is that with the adoption of new fuel injection control systems, you can simultaneously access ignition management, emissions, active braking and safety... all without duplicating components and with a completely transparent system diagnostic process, thus simplifying maintenance.

For example, with the help of ABS braking sensors, the ECM (control unit) can detect if slippage occurs when accelerating and decide 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 parts.
Another advantage that can already be enjoyed with some control units is the adoption of different maps (Economy, Sport, City, Wet...) and changing the vehicle's behavior immediately with the push of a button, resulting in a more manageable, less polluting, and more fun motorcycle.

Frank Burguera

#harleymechanics