I don't know what liberties you are taking with the schematic or the code, but mpguino vss was designed to use a change interrupt on pin 23 which triggers on both a rise and fall. I point a finger at your lack of understanding how it was designed/works
I'm sure you will complain about it though, and have some suggestions for "improvement", at which point I will have to explain that both the edge detection interrupts are being used to distinguish the rising and falling edge of the injector pulse.
Damn newbies. Be a good engineer and look at the schematic and the code and the atmega datasheet please and don't be surprised that making random changes to the code or circuit can break things. There is no hardware OR code ivory tower on this project, they work as a unit. If yours isn't working right, there is only one direction to point.
source data sheet
