Electronic Fuel Injection and The Power Commander
By Scott Holton, J&P Tech

During the first part of December, I had the privilege of traveling to a seminar given by the good folks at the Dynojet Research Company. They are the developers and producers of one of the finest products in the aftermarket called the Power Commander. Today we will discuss the purpose of this device and how we apply it to a Harley®.

Electronic Fuel Injection (EFI) was introduced by Mother Harley® in the 1995-96 model year on some of the FLT series chassis bikes. It is with us today on FLT series bikes and Softails®. I imagine that in the next few years the Dyna® style chassis will also receive this package. The automotive industry has used EFI since the late 70’s with excellent success in today’s more fuel efficient applications.

Before EFI was developed we used carburetors with good success for a very long time. Carburetors are rather simple devices designed to mix a given amount of air with a given amount of fuel. But carburetors do have some limitations. Namely, it is very difficult to provide perfect air/fuel ratios under all conditions with a carb. When a carb is tuned we select the best compromises to give adequate running for a given set of conditions. In order to understand what we ask a carb or fuel injection to do, we need to discuss what an engine requires to make it run.

Under ideal operating conditions a gasoline engine requires approximately 14 parts of air to 1 part of fuel (by weight) to run properly. This 14 to 1 is the air to fuel ratio. The carburetors job is to meter the proper amount of fuel at all throttle settings at all aptitudes. Further complicating things is the fact that a cubic foot of air has one weight at sea level and this weight decreases as altitude increases. It is important to realize that a carb tuned for one altitude is NOT in tune at another altitude. We ask a carb to a lot of things that it simply cannot do. This is why EFI was developed.

Electronic fuel injection provides very precise fuel metering at all throttle positions under a variety of atmospheric conditions. This provides reduced emissions and results in a cleaner atmosphere. The system uses sensors to provide different inputs to an Electronic Control Unit (ECU) that interprets these signals to turn on the injector nozzles in the intake tract for a specific period of time. High-pressure fuel is behind these nozzles and as they open fuel gets squirted in. Some of the sensors used in today’s Delphi injection used on current Harleys® include throttle position, barometric pressure and cylinder head temperature. Each sensor has an electronic range that adds or subtracts fuel in the ECU’s base programming to give us the proper air to fuel ratio. When the ECU leaves the factory, a specific fuel delivery for each throttle position and RPM is programmed into it. This is called a Fuel Map. Each spot on this map is called a cell. (See above diagram). It is very important to remember that the EFI unit WILL ONLY SUPPLY WHAT IT IS PROGRAMMED TO.

Now that we have covered some of the basics lets talk about why we need a Power Commander. In a perfect world any modification we make to our beloved Harleys® would give us the same amount of airflow through an engine. Unfortunately we don’t live in a perfect world and a change, such as putting on new pipes, alters the way air goes through our engine. EFI has no way to change the amount of fuel it delivers to match. A Power Commander (PC) allows us to tailor the fuel curve to match the differences in airflow. This is done by downloading a fuel map into the PC that matches the modifications made to your bike. An alternative to this is to take your bike to a Dynojet tuning center an allow them to build you a custom map. This sounds complex and expensive, but I was quite amazed at the simplicity required to accomplish this task. The motorcycle gets put on a load-control dyno and an exhaust gas analyzer. Then a couple of full throttle roll-ons are performed, a couple of part throttle runs, a steady state run for good measure and poof, you are mapped. Dynojet has done their homework with this software. I came away very, very impressed with the ease and accuracy of tuning.

For the enthusiast that decides not to custom map, included in the PC package is a CD-ROM disc to allow you to make the changes yourself. Dynojet also has a very impressive website(www.powercommander.com) that you may access to get the most up to date pre-mapped downloads available. Every map that is on their site has had that particular combination installed and placed on the load-controlled dyno. No guesswork for these boys. If the combination is there, it’s been tested. For you fuelie guys there is no other system available that allows the tuning flexibility as a PC. One other feature that makes this a very attractive system to use is the excellent customer service provided by Mike, Karl and the excellent tech service staff there. After this seminar I came away trying to figure out how to install EFI on my bike.

I hope we where able to shed some light on how a Power Commander can help us. Till next issue, keep the rubber side down.