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Fuel Management Systems and Mapping

A question we often get is: If I'm only doing slip-ons do I really need to have my bike re-tuned? Simply put if you want your bike to run optimally and avoid the possibility of damaging your engine or other components than you need to make sure your bike is properly tuned. Changing out exhaust systems affects the amount of back pressure to your engine most of which is generated in the muffler section of your exhaust which is what you're replacing when you buy slip-ons. The difference in back pressure affects your bikes Air/Fuel ratio or A/F. Fuel management systems override your factory ECU providing the correct amount of fuel to your engine so that you don't run too rich or too lean causing poor performance and possible damage.

Now that you understand the need for a fuel management system the question is, which should you choose? With a lot of different options on the market it can be a difficult and confusing choice. This article will help you choose the option that is right for you… click here to read the rest of the article.

We will be discussing 4 main options:

  1. Flashing the ECU/ECM
  2. Screamin’ Eagle Race Tuner
  3. Open Loop, or Mapped Fuel Managers
  4. Close Loop, or Auto Tuning Fuel Managers
    • Narrow Band Systems
    • Wide Band Systems

1.) Flashing the ECU / ECM – Your Engine Control Unit (ECU) also referred to as the Engine Control Module (ECM) is the computer that controls key functions related to your engines performance such as your Air / Fuel Ratio (A/F), variable valve timing, etc. This computer contains an Electronically Erasable Programmable Read Only Memory (EEPROM) chip that stores this information without requiring periodic electronic refreshing so that you don’t lose the information if your battery dies or you disconnect it. When you flash your ECU you essentially replace the data on this chip with new data that corresponds to your aftermarket setup and is optimized more for performance than EPA regulations.

As far as we are aware, the only way you can have this done is by an authorized Harley-Davidson dealership. Unfortunately they have a very limited number of options for flashes so generally what you’ll end up with is something pretty generic and it won’t be specific to your bike and setup. To make matters worse we’ve been told that now the only flashes that H-D will do affect valve timing curve only and not fuel so you will most likely be running too lean even if you do have your ECU flashed.

2.) Screamin’ Eagle Race Tuner – Another Harley-Davidson product that you’ll often times hear about is their Screamin’ Eagle Race Tuner. This is Harley’s version of an open loop or mapped unit which we’ll discuss in the next section as well. The SE Race Tuner works by overriding the ECU using a custom map generated by putting your bike on a dyno machine. The advantage is that the map is tuned specifically for your bike and setup. The disadvantage is that if you change your setup or ride at a different elevation, etc. the only way to make an adjustment to the system is to bring it back in and put it back on the dyno which can be expensive.

3.) Open Loop, or Mapped Fuel Managers – Open loop systems work on the same principles as the SE Race Tuner mentioned above. The advantage to going with an aftermarket brand over the Race Tuner is that often times the units will come pre-loaded with or you will have the ability to download a map for your bike and setup, which eliminates the need to put your bike on a dyno saving you a significant amount of money. The other advantage is that often times these open loop systems have the ability to make minor adjustments to the map on the fly by adding or subtracting a % of fuel over a given RPM range without having to install a new map. This way if you do make a minor change or are riding in a slightly different condition you can manually make tuning adjustments to compensate for the changes.

4.) Closed Loop, or Auto Tuning Fuel Managers – Out of the factory your bike will run in an open loop mode most of the time, meaning it will take all its information from the static map loaded on the ECU. In more recent years Harley-Davidson has started fitting their exhaust systems with O2 sensors which take readings from your exhaust and determine if you’re running too rich, too lean or just right. This allows your bike the ability to run in a closed loop mode meaning it can take the data from the O2 sensors combined with the map and constantly make adjustments. Unfortunately as mentioned before even bikes with O2 sensors installed run in an open loop mode the majority of the time and only switch to closed loop mode when you really get on the throttle. Although unconfirmed out best guest for the reason for this is EPA regulations and requirements. The other reason may be that as long as you’re running a factory setup, this system works just fine. Auto tuning fuel managers work on the closed loop principle and although the way they go about it varies from product to product the main idea is still the same. One main difference between some of the auto tuners on today’s market is the type of O2 sensors they use which we will discuss below:

a.) Narrow Band Systems – Your bike comes out of the factory equipped with narrow band O2 sensors which some auto tuners on the market utilize. These types of systems work well if you’re planning on doing relatively minor Stage 1 changes such as changes in exhaust and/or adding a high performance air filter and will save you a lot of money compared to a wide band system. However if you’re planning to do heavier Stage 2 modification such as performance cams you’ll be better off going with a wide band system.

b.) Wide Band Systems – Wide band systems come with wide band O2 sensors that replace your factory narrow band sensors and allow for a higher, more accurate rate of readings. Although more expensive than the narrow band options these systems are a must if you’re going to be doing heavy modifications to your bike.