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How the Harley ECM (Electronic Control Module) Works with Dynamic Tuners

The Harley ECM

2006 & Up

How it Relates to Tuners & Dynamic Tuning


Making a bike run stronger, smoother & cooler is something most of us want to do...


Questions about adjusting the tune when adding a high flow air cleaner, or high flow exhaust, or both, are asked many times each day.

Starting with the basics:  There are three main types of HD engines that use EFI-

  1.  Sportster Evolution

  2. Twin Cam

  3. Milwaukee-Eight


The Sportster and the Twin Cam come from the factory tuned too lean. 

This is done by HD to meet EPA standards, but results in the bikes running hot, having hesitation on acceleration, and generally not running as strong or smooth as they could.


The Milwaukee-Eight (M8) is Not too lean from the factory.  A report on that can be seen HERE.


Closed Loop & Open Loop Basics-


Closed Loop is the part of the tune where the ECM keeps the AFR (Air Fuel Ratio) at a predetermined setting during low-mid throttle/cruising.  This is where the majority of riding is done and where the settings are Too Lean on the Sportster and Twin Cam.


Open Loop is the part of the tune where the ECM richens up the tune for high-mid to full throttle acceleration/high load riding.  Relatively little riding is done in this area of the throttle and the AFR is not too lean from the factory.


All Harley ECM’s have what HD calls Adaptive Learning.


There are two ways the Electronic Control Module (ECM) adapts:


First, let's look at what input the ECM receives, so we know what it has to work with to make any "Adaptive" changes-


1. CKP - (Crankshaft Position Sensor): Basically this sensor monitors the crankshaft speed and position. The ECM uses the inputs from the sensor to determine what stroke the engine is in so it can deliver the fuel and spark at the desired time... 


2. MAP - (Manifold Absolute Pressure): The ECM uses the inputs from this sensor to help calculate how much air is entering the engine. 


3. IAT - (Intake Air Temperature): The ECM uses the inputs from this sensor to help calculate how much oxygen exists in a particular volume of air.. 


4. ET - (Engine Temperature): The ECM uses the inputs from this sensor to determine engine temperature... 


5. TP - (Throttle Position): Provides input to the ECM as it reacts to throttle shaft rotation...     These signals indicate throttle position, if the throttle is opening or closing and how fast it is opening and closing... 


6. VSS (Vehicle Speed Sensor): Provides input signals to the ECM to indicate the speed of the motorcycle... 


7. BAS (Bank Angle Sensor): If the motorcycle leans over more than 45 degree's from vertical... If the ECM receives this input for more than one second it assumes the motorcycle has fallen over and shuts down the fuel management and ignition circuit...


8. O2 Sensor: They are switching type sensors (stock HD's are narrow band sensors used in closed loop systems) they provide inputs to the ECM based on the amount of oxygen is being seen in the exhaust system... 


9. ISS (Ion Sensing System on Twin Cam only): It detects detonation or engine misfire in either the front or rear cylinder by monitoring the electrical energy at the spark plug following every time spark...If an abnormal level of energy is detected across two or three spark firings the ECM responds by retarding the spark timing in the affected cylinder as needed to eliminate it... 


All of the above sensors give data to the ECM to allow it to ADAPT to the ever-changing environment. This is one of the ways the ECM ADAPTS.


The second way the ECM ADAPTS is via "Adaptive Fuel Value" or "Adaptive Fuel" (reference the HD brand Tuners to see that this is a feature of the ECM) This is commonly what is referred to as the Adaptive Learning Mode.


Adaptive Fuel is known generally in the EFI world as Long Term Fuel Trim (LTFT).


When in closed loop the ECM uses the information from the above list to calculate airflow, load, temperatures, throttle position, to adapt and maintain the targeted AFR in the closed loop section of the map.


It then uses the o2 sensors to determine what the AFR actually is. If there is a difference, the ECM makes an adjustment real time to the closed loop map, AND stores the difference in an "Adaptive Fuel Value" cell for future use in Open Loop. (again, reference the HD Brand Tuners to verify that there is an Adaptive Fuel Value" that is stored in the ECM and that is constantly changing)


Over time (30-120 minutes of riding) the Adaptive Fuel Value develops a correction profile that is applied to each cell of the map in open loop.


To put it another way, when the ECM sees the closed loop values constantly being richer than expected (like when using an XIED family product), the Long Term Fuel Trim (Adaptive Fuel Value) is increased, resulting in a richening up of the open loop values.


 Click HERE To See a Selection of Tuners for Your Harley