Harley-Davidson 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 the following EFI-Equipped models: 2001
- later Softail, 2002 - later Touring, 2004 - later Dyna, and 2002 - later V-Rod. That said, it is
assumed that the user of this product has a thorough understanding of internal combustion
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 the following EFI-Equipped models: 2001 -
later Softail, 2002 - later Touring, 2004 - later Dyna, and 2002 - later V-Rod.
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
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.
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 highpressure
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
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
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
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
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
When the engine is running the series of events typically follows the process below:
The ECM monitors the CKP, TP, IAT & MAP sensors telling it engine rpm, throttle
position, intake air temperature and manifold absolute pressure.
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.
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.
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.
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.
When the engine is experiencing a temporary condition such as when the bike is being
started on a cold morning, it uses additional Look-up tables that are also programmed into
the ECM. For example, a cold engine that's being cranked to start rotates at a very low
rpm and needs additional fuel. The ECM reads the ET and CKP sensors, which tell it
the engine is cold, and that it's rotating at cranking speed. The ECM then refers to a
Cranking Fuel look-up table and directs the fuel injectors to remain open longer,
(increasing their pulse width) which delivers a richer air/fuel mixture for starting. It also
directs the IAC to open to its programmed number of steps to allow enough air into the
engine for starting and idling.
When the engine starts to run the ECM sees the higher rpm and then refers to a
Warmup Enrichment look-up table that it uses to add the additional fuel needed while
the engine is still cold. The table is designed to diminish its affect, (referred to as "decay
value") to zero as the engine comes up to operating temperature.
Heat Management System
The ESPFI systems on the following EFI-Equipped models: 2001 - later Softail, 2002 - later
Touring, 2004 - later Dyna, and 2002 - later V-Rod also incorporate a sophisticated heat
management system that operates in three-phases to keep things cool in extreme conditions.
Phase I: If the ECM detects engine temperature above approximately 300° F while moving
or stationary it reduces the idle speed. A lower idle speed produces fewer combustion events
per minute and that reduces engine heat.
Phase II: If the ECM detects an engine temperature that's still drifting higher while moving
or stationary it richens the AFR. An increased amount of fuel in the air/fuel mixture has a
cooling effect on the engine.
Phase III: If the ECM detects an engine temperature that's still drifting higher while moving
or stationary it directs the fuel injectors to skip, (only when the bike is stationary) and not
deliver fuel on every intake stroke. This limits the number of combustion events taking
place, which produces less heat.
The 3-Phases just described function seamlessly, and the rider may not notice the
transition from one phase to the next.