I have been working on the code for the piggy back ECU over the last few days. I am currently using an ardunio micro to simulate the factory ECU by creating 6 injector pulses at variable pulse lengths (engine load) and frequency (engine RPM).

The injector pulses are read by an arduino mega 2560. The engine RPM is calculated and manifold pressure is read. These two variables are used to read from an 18 x 16 array (the fuel map) this then used to extend the open time of the injectors after they have been closed by the factory ECU.

At the moment it all seems to be working quite well untill the injectors reach a 100% duty cycle.