Why would I want to switch fuel maps?

I have an aftermarket fuel tuning device on my motorcycle that can store two different fuel maps, and can switch between fuel maps on demand via an external input (e.g., a button). I wanted to calibrate one fuel map for pure performance and smoothness, and the other fuel map for fuel economy. This gives me the “best of both worlds”. I can use the “economy” map whenever I’m cruising fairly steadily, then with the push of a button, have maximum power and smoothness whenever I want/need it. But pushing a button is annoying, so I would tend to leave it in the “power” mode most of the time for guaranteed smoothness around corners and other city driving situations. I would only switch to “economy” mode when I was on the freeway.

Automation is better than a manual button

Why press a button if I could be lazy and automate the decision to switch fuel maps? An automated process isn’t annoyed by pressing a button, so it would switch me into “economy” mode more often to help me save money on gas! So I developed a simple electronic device with a microcontroller that monitors the throttle position and engine speed, and automatically switches between fuel maps. If the throttle position and engine speed are fairly steady, then I’m “cruising” and the “economy” fuel map should be used. Otherwise, the “power” fuel map should be used to ensure I have smooth, predictable, and maximum power delivery immediately if needed.

Here’s what the custom electronics look like. It’s just a microcontroller and a few components to power the microcontroller from the motorcycle’s 12V electrical system.

There’s a lot of details involved, like smoothing the input signals, setting reasonable thresholds for rates of change that mark the transition between “steady” and “not steady”, and applying a “cooldown timer” to prevent switching back to “economy” mode if inputs are only very briefly “steady”. I generally calibrated it to only use the “economy” mode when I’m really sure that I’m cruising fairly steadily.

Here’s an example of a data log showing vehicle speed, engine speed (RPM), throttle position (TP), and the fuel map selection input (DigIn). The top most line in the graph is high when the “power” fuel map is selected, and low when the “economy” fuel map is selected.

Read More

I documented my progress and some of the complexities/complications I encountered along the way on the FJRForum motorcycle forum. You’ll also find links to other forum threads about the fuel tuning device that I’m using.