And I don't know how much it takes to open them half way.
This will tell me how much of the injector nozzle is open
You don't seem to understand that the injectors are fully open or fully closed.
They are not held half open, they need the full pressure and flow of fuel for a particular time to meter out the required amount of fuel.
What electronic test equipment do you have to analyse the engine?
Because you will be trying to monitor a high voltage signal in a capacitive circuit, I'm not sure how the injector driver circuit or the injector itself will react to any load.
The reason you could not run flex fuel without the kit is probably because of the fact that the engine will knock and that ECU does not have the range to adjust.
As you point out the TMAP is read and its signal monitored, but in conjunction with the engines knock sensor, it sounds like the kit is just to let you run flex fuel, any extra power I don't know.
Reading signals from TMAP sensor is nothing like reading injector pulse timing
But what has this to do with your extra injectors and added fuel feed?
For one thing, by applying a little less electricity, the piezo crystals expand less so the injectors can open partway. A smaller opening means a longer injection time, which is beneficial when trying to accurately inject a tiny amount of fuel, such as when a car is nearly coasting.
The voltage matters on how much they open.
The reason I brought up the flex fuel kit was because I thought it was similar. It is reading a signal 0-5v and then acting in real time based on that.
My idea behind my project was to read the injector signal and act on it in a way to fire another injector in the similar ratio. The additional injectors wouldn't begin to operate until the piezo are operating harder. So no reason to spray fuel from the additional injectors at idle.
If 0 = Idle and 100 = full throttle at 7k rpm. I could get the pwm at idle, the pwm at full throttle, and then find a middle ground to use for activating the additional injectors.
As far as the Oscilliscope. If I buy one, monitor the injectors at different rpms/loads/etc. Then I can build a table.
At X RPM, X Load, X Boost, X etc the injector is firing at X pulses, X Voltage.
Then I can begin to spray the additional injectors when the piezo injectors are starting to tank and can't keep up.