do you already have a DC source to get this 110-140vdc from, or do you need to build that too?
This is part of the problem too. I am not set up with this yet.
do you already have a method of manually switching the injectors?
No, i really have nothing as of yet except the idea.
If you can get the switching to the point where all you have to do is apply a logic-level signal to your switching circuit with the right pulse width, then the rest should be a piece of cake with a microcontroller; generating a pulse between 3-7ms and keeping track of the number of pulses would be very simple.
This is what i need more info on. Do you have any links to something of this mannor for me to look at?