Fuel Injection Tuning

Fuel Injection Tuning

Motocross fuel injection is based on an “Open Loop” system.

Definition: Open Loop

Open loop simply means there is no feedback of the result to the ECU (Engine Control Unit). In our case, it means there is no sensing or measuring of the exhaust gas to see how the bike is running. The fuel that is being injected is determined by the RPM and throttle position, derived from the fuel injector pulse width numbers stored in the fuel maps, and is trimmed for environmental conditions due to air temperature, air pressure and engine temperature.

Factory engineers have set the ECU to provide a specific AFR (Air Fuel Ratio) for an exact set of circumstances: compression ratio, cam timing, exhaust system, port design, throttle body size, combustion chamber shape and fuel type.

The ECU map has a preset amount of fuel and ignition timing that will only be correct in these conditions.

Changing any of these conditions, such as replacing the exhaust system with an after market type will have an effect on the required fuel and possibly the ignition timing in some cases. As more and more changes are performed, the factory tuned conditions will move farther away from the optimum. What I am saying is, as you invest in aftermarket bolt-on products it will have a negative effect on the proper AFR; a power gain may be felt, however it may only be 80% or 90% of what it could be if tuned correctly for the new conditions.

Now, this being the situation, “What’s a guy to do”? Fuel injection being newly introduced to our sport, very few have dedicated the necessary time required to become proficient at this time consuming endeavor. Personally, I have spent the better part of the last four years in my dyno room, honing my skills and developing the next generation of injector/throttle body design. This challenge has pushed me to learn more about ECU tuning than I had ever imagined.