Harley-Davidson Electronic Fuel-Injection Tuning Aids

Conclusions

If you are modifying a Harley EFI (Delphi or Magneti-Marelli) engine with more than a high-flowing air cleaner, chances are you will need to adjust the engine's fuel curve to achieve maximum power and smooth ridability. Although nothing is set in concrete, here are a few things to consider when modifying an engine with a Harley-based EFI system

Harley-Davidson offers a wide selection of ECM recalibration "downloadable maps" for its SE Stage I and Stage II kits that often get the job done. Fuel-curve adjustments for minor performance upgrades-high-flowing air cleaners, free-flowing exhaust systems, and some mild cams-can often be handled by low-cost pot-style devices. Once you install moderate to big cams (and sometimes even mild cams) or venture into the realm of 100-plus cubic-inch displacement, you're probably going to need a map-based device offering a wide range of fuel curve adjustments, such as a Dynojet Power Commander or Harley-Davidson Race Tuner

Sometimes you can download a map to get the tuning close, then do final tuning with an add-on or map-based device. Moreover, if you are going to make modifications in small increments over a long period, it is usually more cost-effective to start with a map-based SE Race Tuner or Power Commander, because that's what you'll need in the end to get the tuning correct. Before making a decision on purchasing a tuning device, make sure you really need one. Some mild engine combinations don't need anything beyond the stock ECM. Finally, make sure downloadable maps are available for your engine combination and that you have a local tuner who's knowledgeable about the device you are considering. A knowledgeable and honest tuner is the best friend you can have when delving into the complex world of EFI. Happy tuning!

EFI Fuel Map

An EFI map is a multi-dimensional look-up table that's stored (downloaded) into the fuel injection's computer (called the Electronic Control Module, or ECM, by Harley-Davidson). A map is created for a specific engine parts combination and is used by the ECM to adjust the fuel delivery of the fuel injectors based on throttle position, rpm, and other critical factors. In addition to the fuel curve, maps can also control ignition timing, rev limit, start-up, and warm-up functions. For stock Harleys, the map is preprogrammed and loaded into the ECM at the factory.

By using a PC, the ECM and some add-on modules can be reprogrammed with a custom map designed for a modified engine combination. A custom map increases or decreases fuel delivery from the stock map settings to meet the needs of a custom performance engine. Custom maps for specific parts combinations are available from various manufacturers, and they can be created ad hoc in the field through dyno or road testing.