Understanding Harley EFI Systems

How It Works

Before discussing how the Screamin' Eagle EFI Tuner kit works it is important to understand how the Electronic Fuel Injection system functions on 2001 and later Softail and 2002 and later Touring model Harley-Davidson motorcycles. That said, it is assumed that the user of this product has a thorough understanding of internal combustion engine operation.
Harley-Davidson Electronic Sequential Port Fuel Injection System, (ESPFI)
This completely new engine management system was released starting with select 2001 model year Softail motorcycles. This system is a speed/density, open loop, sequential port fuel injection design that also controls spark timing and spark intensity.
Speed/Density System – When the ECM monitors manifold air pressure, air temperature, throttle position and engine rpm to manage fuel delivery.
Open Loop Control – When the ECM monitors sensors positioned on the intake side of the engine and does not monitor the end result of internal combustion at the exhaust.
Sequential Port Fuel Injection – When the injector nozzle is positioned in the manifold near the intake valve and is precisely timed to deliver fuel to each cylinder.
This ESPFI system is the exclusive design used on select 2001 and later Softail models and select 2002 and later Touring models.
Current ESPFI Components
The following is a list of the major components of Harley-Davidson’s current ESPFI system. It is important to have an understanding of what these components do before learning how the ESPFI system functions. Refer to the appropriate Harley-Davidson Service Manual for the vehicle you are working on for additional information on component design and function and for the physical location and testing procedures for each individual component.

ECM – Electronic Control Module – this is the brain of the system that collects input signals from multiple sensors, makes decisions and sends output signals to deliver fuel and spark to the engine.

CKP – Crank Position Sensor – this sensor provides input signals to the ECM that indicate engine rpm, (how fast the engine is running in Revolutions Per Minute). The ECM also uses these inputs to determine what stroke the engine is in so it can deliver the fuel and spark at the desired time.

MAP - Manifold Absolute Pressure – this sensor provides input signals to the ECM and reacts to intake manifold pressure and ambient barometric pressure. Intake manifold pressure reflects changes in engine speed and load. Ambient barometric pressure reflects changes in atmospheric pressure caused by weather conditions or changes in altitude. The ECM uses the inputs from this sensor to help calculate how much air is entering the engine.

IAT – Intake Air Temperature – this sensor provides input signals to the ECM as it reacts to the temperature of the air entering the engine. For example, hot air has less oxygen in it than cool air. The ECM uses the inputs from this sensor to help calculate how much oxygen exists in a quantity of air.

ET – Engine Temperature – this sensor provides input signals to the ECM as it reacts to the engine temperature of the front cylinder head. The ECM uses the signals from this sensor to determine if the engine is at operating temperature, or warming up.

TP – Throttle Position – this sensor provides input signals to the ECM as it reacts to throttle shaft rotation, telling the ECM throttle position, if the throttle is opening or closing, and how fast it’s opening or closing.

VSS – Vehicle Speed – this sensor provides input signals to the ECM to indicate if the bike is moving or sitting still. It is used mostly to assist the control of idle speed.

BAS – Bank Angle Sensor – this sensor is located in the turn signal module and it sends a signal to the ECM if the bike leans over more than 45° from vertical. If the ECM gets this signal for more than one second it assumes the bike fell over and it shuts down both the fuel management and ignition circuits.
Ion Sensing System – this system uses ion-sensing technology to detect detonation or engine misfire in either the front or rear cylinder by monitoring the electrical energy at the spark plug following every timed spark. If an abnormal level of energy is detected across 2 or 3 spark firings the ECM responds by retarding spark timing in the problem cylinder as needed to eliminate it.
Fuel Injectors – the fuel injectors are electric valves that open and close to deliver a high-pressure spray of fuel directly at the intake valve. They are controlled by output signals from the ECM to deliver fuel at a precise moment. If more fuel is needed, the ECM will signal the injector to remain open for a longer period of time. The period of time is known as the injector "pulse width" and is measured in milliseconds. One method of rating fuel injectors is by their flow rate – such as in gm/sec, or grams per second.

Electric Fuel Pump – a 12-volt high-pressure fuel pump, (located in the fuel tank) supplies fuel under pressure to the fuel injectors.

Fuel Pressure Regulator – a mechanical device that controls fuel pressure to 55-62 PSI by returning excess fuel from the fuel pump back to the fuel tank.

IAC – Idle Air Control – an electric valve that’s threaded, (each rotation is a "step") and controlled by output signals from the ECM to open and close as needed to allow enough air into the engine for starting and idle operation. The greater the number of IAC steps, the greater the amount of air enters the engine through the IAC passages.
As mentioned, the ECM is the brain of the ESPFI system. And, like our own brain, it has memories and it makes decisions. The ECM memories are located in Look-up tables, (see example Air Fuel Ratio table below). The ECM uses several different Look-up tables to make decisions on fuel and spark management. The Look-up tables that are in constant use by the ECM are the VE, (Volumetric Efficiency), AFR, (Air Fuel Ratio) and Spark Advance tables.
One type of Look-up table the ECM always uses is for VE, which is a percentage rating of how much air is flowing through the engine while running as compared to its theoretical capacity. For example, an engine with a displacement of 88-cubic inches running at 5600 rpm at full throttle has a theoretical airflow capacity of 100% when it flows about 143-cubic feet of air per minute, (cfm). If the same engine flows 107cfm at 5600 rpm it would have a VE of about 75%. And, if the engine flows about 157cfm at 5600 rpm it would have a VE of about 110%. That’s right, the VE can exceed 100%, especially in high performance engines that have improved airflow through the engine. VE reacts to engine speed and to anything that increases or decreases airflow through the engine. The VE Look-up tables in the Screamin' Eagle calibrations are calculated from data they gather while testing live engines on engine and chassis dynamometers, and with data acquisition equipment in conjunction with track testing.
Overview of How the Harley-Davidson ESPFI Functions
The front and rear cylinder VE Look-up tables, which are programmed into the ECM, tell the ECM how much air, (volume) is flowing into the engine at different engine rpm and throttle positions.

The ECM also monitors the intake air temperature and manifold absolute pressure, which provide it with an indication of air density, or the amount of oxygen contained in a volume of air.
The AFR, (Air Fuel Ratio) table, which is programmed into the ECM, tells the ECM what AFR the engine should require under specific engine loads, (engine load is determined by monitoring manifold absolute pressure and engine rpm) to produce the performance that’s desired.
The front and rear Spark Advance tables, which are programmed into the ECM, tell the ECM the spark advance desired for specific engine loads to produce the performance that’s desired.
When the engine is running the series of events typically follows the process below:

1. ► The ECM monitors the CKP, TP, IAT & MAP sensors telling it engine rpm, throttle position, intake air temperature and manifold absolute pressure.

2. ► The ECM looks at throttle position and engine rpm when it refers to the VE Look-up tables. From this information the ECM knows the volume of air that should be entering each cylinder at this moment, under these present conditions.

3. ► At the same time the ECM looks at intake air temperature and manifold absolute pressure to calculate the density of the air entering the engine. Air density tells the ECM how much oxygen is in the air entering the engine.

4. ► Now the ECM knows exactly how much oxygen is entering each cylinder and it refers to the AFR Look-up table for the AFR that’s desired. It then sends the appropriate output signals to the fuel injectors to achieve the AFR it has been programmed to deliver for the current engine rpm and engine load.

5. ► The ECM also refers to the Spark Advance Look-up tables for the desired spark advance for each cylinder according to the current engine rpm and engine load. The ECM then sends output signals to the front and rear ignition coils to deliver the desired timing of the spark for each cylinder.

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