Introduction to Harley-Davidson® Electronic Sequential Port Fuel Injection (ESPFI)
By Dave Bickford "Ultraboy"

In this segment, we'll attempt to explain the components and operation of the ESPFI systems offered on 2001 and later Softail®, 2002 and later Touring, 2004-2005 Dyna®, and 2002 and later V-Rod motorcycles. Ready? OK, let's start out with some terms.
The Harley-Davidson ESPFI system is known as a Speed/Density, Open Loop, Sequential Port Fuel Injection system, that controls both fuel flow, and spark timing. Let's further explain those three terms.

Speed/Density - An Electronic Control Module (ECM) monitors manifold air pressure, air temperature, throttle position and engine rpm to manage fuel delivery.

Open Loop - 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 - Injector nozzles are positioned in the manifold near the intake valve and are precisely timed to deliver fuel to each cylinder.

Still with me? OK, let's dig into the components that make up the system, what they do, where they are, and what they are commonly called.

SYSTEM COMPONENTS

ECM - Electronic Control Module - Sometimes called an ECU, or Electronic Control Unit, is a small microprocessorcontrolled box, or "the brains" of the system that collects all of the input signals from the sensors, and makes decisions based on those sensor inputs, and then sends output signals to deliver fuel and spark to the engine. On Softails®, it's located under the seat, on Baggers it's under the side panel.

CKP - Crank Position Sensor - This sensor provides input signals to the ECM that indicate engine rpm. 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. It's located on the front of the motor. It's that thing that's in the way when you change your oil filter.

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. It's located in the intake manifold on top, just behind the throttle body.
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 contains less oxygen than cool air. The ECM uses the inputs from this sensor to help calculate how much oxygen exists in a quantity of air. It's located in the throttle body.
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 still warming up. It's that probe in the front Cylinder head, on the left side.

TP - Throttle Position - This sensor provides input signals to the ECM as it reacts to throttle shaft rotation, telling the ECM where the throttle is, as well as if it's opening or closing, and how fast it's opening or closing. It is at the rear end of the throttle blade.

VSS - Vehicle Speed Sensor - 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 degrees. If the ECM gets this signal for more than one second it assumes that the bike fell over and it will immediately shut down both fuel and ignition.

Ion Sensing System - This system uses i