Injector dead time on scope

what if for example , i bought second hand injectors (dead time unknown) , can i make the engine run at lets say 3milliseconds ecu injector setting , and then with my scope catch a voltage to time image of the voltage (yes i need to mirror the image because it is negatively switched) and watch when the injector really opens ?

would that be acurate ? more acurate then tuning the ecu without dead time compensation ?

On a ms based ECU (MoTeC Mx00 series for example) this would be a good start, and better than using no or the wrong information, as you somewhat "tune around" the roughness of the data when doing the mapping. However, with a VE based ECU (MoTeC M1, new Haltech, etc.) then the data will not be as accurate as needed for the ECU to make the calculations as they need to know the mass of the fuel injected per pulse at different voltages and pressures as well.

You need to do it at a range of pressures and voltages in order to get the best data possible.