MAP Selection

ECU Input: Ignition/Fuel Map Selectors

The Map Selector signals are used to implement the now infamous "derestriction" available on the first few years of Gen 1 Aprilia Rotax ECUs. The term "Map Selector" refers to the fact that these two wires select which set of ignition & fuel maps will be used by the ECU. If you leave things alone, the ECU uses map set #0, or the stock maps for fueling and spark control. By clipping the derestriction wire, the ECU would shift over and use map set #1, or the high-performance maps.

What is interesting to me is that while everyone was aware that there was one Map selector wire, it turns out that there are two different map selector wires! Reading the ECU software shows that the ECU actually tests for a secondary map sensor wire, although in a slightly inconsistent fashion to how it tests for the first map selection wire. If this software issue were fixed (and it would not be too tough), it would be theoretically possible to add yet another pair of ignition and fuel map sets to the software, although that would be a much more involved software change. If that got done, you could add a pair of switches to the ECU that would allow you to select from four maps instead of two.

Here is a snapshot of the MS1 Map Selector "derestriction" input:

The circuit is extremely simple, and is identical to the DIAG/Test circuit. The wire labeled MS1 (above) represents the wire in the external wiring harness that can be cut or not. With the external wire un-cut, the input to the inverter is grounded. If the wire is cut, the pull-up resistor R621 will pull the inverter input to a logical HIGH state, which will cause the inverter to drive its output LOW. By reading the state of the PG3 input, the processor can tell if the wire has been cut or not: if PG3 is LOW, the wire has been cut.