I am tracing the operation of the ECU. I want to supply it with power but what is the ECU voltage input that I should supply?
If you're talking about a regular 12V battery vehicle, then the ECU is likely to work from 7V until 14V with no problem. That's the usual requirement for this kind of component.
It needs a minimum of 9.6v from battery power from a 12v system if the battery is close to being dead lets say 8v left on it...then the car wont even turn over
I used a Buck and Boost controller. Set it at 12.39 volts D.C. and forget it. The ECU line also powers the Distributor, so as to protect both ECU and vehicle Distributor.
It entirely depends on what your trying to do with it.
To power it on usually 9-14.5 volts will be fine.
However most modern (12years or so or newer) are smart enough to block certain functions unless there is at least 12.6v or in some cases 13.5v.
So as said it depends on what you want to do, if you want to power it up to test it with a diagnostic tool or its basic function just power it with a good fully charged 12v battery or even better a AC-DC power supply.
Put if you are trying to reflash/reprogram the ECU, fully test it or communicate with it then I would power it with a AC-DC power supply or battery support unit with around 13.5v