Harley-Davidson Electronic Fuel-Injection Tuning Aids

The Dynojet Power Commander is another add-on device that connects in series between the ECM and fuel injectors, but it differs from basic pot-based add-ons because it is a map-based module that allows for the reprogramming of fuel maps. Therefore, it will be covered below under map-based reprogrammers.

Map-Based Reprogrammers

Once your engine gets into the 100-plus cubic-inch range, has big cams installed, or has heavy cylinder-head porting, pot-like devices cannot segment the rpm ranges into small enough portions to satisfy the engine's air/fuel requirements. That is where map-based devices shine. The most capable and generally the most costly EFI tuning aids are map-based modules. Map-based tuning aids contain one or more look-up tables called maps

for controlling fuel, ignition timing, rpm, start-up, and warm-up functions, just to name a few. The tables are finely divided into many small cells for close tuning over a wide range. Each cell represents a number indicating the percentage of fuel change, either plus or minus from a base value, based on various engine data, such as rpm, throttle position, and so on. We'll cover two map-based reprogrammers: the Dynojet Power Commander (hardware- and software-based device) and the Harley-Davidson SE Race Tuner (software-based).

Dynojet's Power Commander is an add-on computer that connects in series between the ECM and fuel injectors. The add-on computer stores maps that can be reprogrammed with a personal computer (PC) for a wide range of modified engine combinations. Separate fuel and ignition tables are available for both front and rear cylinders, and the newest models allow the engine's rev limit to be raised above the stock value. Three buttons are provided on the computer, allowing for manual richer or leaner adjustments in 2,000-rpm-wide bands. Power Commanders include a CD-ROM with current maps for many engine combinations, and new maps can be downloaded from the company's website.

The Harley-Davidson Screamin' Eagle Race Tuner is a software map-based reprogrammer that does not require an add-on module because it has the ability to reprogram the stock ECM. The Race Tuner software program comes on a CD-ROM along with a hardware "key" (adapter) that allows connecting a PC to the stock ECM. Once the Race Tuner uploads a new map into the stock ECM, the PC and hardware key are removed, and no additional parts remain on the bike.

In addition to allowing fuel, ignition, start-up, warm-up, and rev-limit modifications, the Race Tuner also includes a function for setting injector size, which allows for greater tuning flexibility. Several operating modes are available, including basic, advanced, and data monitoring. The Race Tuner and Power Commander are similar in that table cells represent the percentage of change, either plus or minus. One thing that is different, however, is that the Race Tuner will not allow you to download a map from it as the Power Commander will.