Aprilia Fuel Injection

Back in 2003, I bought an Aprilia Tuono motorcycle. It was my first bike that was fuel injected. I was fascinated with how it worked, and being an embedded computer guy, I felt the need to take one apart and see what was going on. That started a multi-year project to figure out how to hack it. As part of the project, I made a website that described my understanding of how the system worked. As time passed, my web-hosting site went away, and the website disappeared. I didn't feel like reworking many, many pages of HTML and finding a new hosting service so it just vanished. Now that I am using Google Sites as a webhosting service, it might be time for a new project to resurrect the website. After all, it is still a great motorbike, and there are a lot of people around the world who still own an Aprilia with the same V990 engine.

It will take me a fair while to get every page converted, but the goal is to recreate the information from that original website.

Gen 1 Aprilia Fuel Injection Operation

This project will delve into the inner workings of the Gen 1 ECU (Electronic Control Unit) used to control the fuel injection system on Rotax-powered Aprilia motorbikes from 1999 to 2005. Starting in 2004, the Mille used a different ECU, but the Tuono still used the original ECU model through 2005.


I'm not exactly sure. Maybe because we can't mess with carburetors any more, so this represents the next frontier in not leaving well-enough alone.

What really intrigued me was that for the first couple of years, Aprilia bikes stored a pair of maps in their processor memory. The bikes were sold in a so-called "restricted" form to meet worldwide noise and emission standards. However, it soon came out that these same bikes could be "derestricted" to a higher state of tune by performing a short set of operations.

Derestriction Process

A fairly complete list of the EPROMs that could be derestricted can be found here. For those EPROMs that are derestrictable, the derestriction process runs as follows:

  1. Remove a baffle from the exhaust pipe

  2. Pull a restrictor plug out of the airbox inlet

  3. Clip a particular wire going into the ECU

The free-thinking Aprilia software engineers had designed the software to detect this very situation, and respond by activating a secondary "performance" set of fuel and ignition maps. Net result: approximately 10 extra HP at the rear wheel.

You just gotta love that!

But nothing good lasts forever. From 2002 and onwards, the North American models had the secondary maps disabled so clipping the wire has no effect. The story I heard is that other manufacturers complained about this technique for making it so easy for owners to get access to "closed-course" performance, maybe because they didn't think of it first. In any case, Aprilia backed off from supporting this feature.

Even so, it indicated that the basic ECU box could support all kinds of interesting performance modifications, if one could only figure out how it worked. Now there was a challenge. A bit of decoding, a bit of analysis, a few thousand hours of work...

Hey, I've spent more time on less.


The 'How' is the most interesting part. My intent is that people who have little or none computer hardware or software experience should be able to get something out of these pages. Even so, there will be plenty of detail for those inclined to take it to a deeper level of understanding.

First off would be a short overview of what the Aprilia fuel injection system does. Getting from the overview to the specifics is fundamentally a two-step process although I will admit that each of the steps is pretty large:

  1. Work out how the Aprilia ECU hardware operates

  2. Figure out how the Aprilia ECU software works

After working out how the ECU hardware and software operate, the ultimate goal would be to use this knowledge for tuning purposes. And that would be yet another large project.

What can I say, any project that starts off with violating a warning label is going to be fun:

And it was fun. I learned a lot in the process:

If you are interested, read on...