This might be totally off base but I have a feeling that I can get the injector constant pretty close by the following method. Keep in mind this might not work with all ecm's because they use different ways of calculating the fuel requirements.
Let's say I set my injector constant to 100 and fuel pressure is at 28psi on unknown injector size. I then use lockers tune for a BLM of 128 across the whole board. Okay, done that, now enter in a set PE AFR of 12.8 : 1 in the table, next set highway mode to all 16 : 1 , drive around datalogging with wideband and see if these AFRs are in the ballpark or not. If not, adjust injector constant and Vol Eff tables accordingly and try again. Once this is down you'll have a GM computer that knows exactly what kind of motor it's having to control. No lies = happy computer, trust me, it likes the truth.
Anybody see anything apparently wrong with this method? I know it isn't perfect but I figure it'll get me close enough to be better off.
If this is a waste of my time then post that opinion so as to save me time.
I know somebody that has an injector flowbench, maybe I'll just talk to him and see if he can flow them for me at different fuel pressures.

 

Do you mean beginning with a known injector size, and good calibration?. And then trying to Recal with an unknown?.
If so, then yes.

If an unknown cal with unk injector size your in for alot of work.
That gets to the stage of doing a from scratch calibration, that I mentioned.

 

Seems to me, with two variables (VE and BPW) you won't be able to figure out what BPW should be.

Lets say you are idling cls loop at 40KPA X 800rpm. There are any number of BPW and VE combinations that would result in the target 14.7:1.

WOT and Hwy mode are just calcs off the 14.7:1 right? So, it won't make any difference what the BPW or VE's are.

100 BPW and 40 VE might result in 128 BLM's while 135 BPW and 15 VE might give the same result

or maybe I've got it sideways........

 

Yes, but adding PE as a means of calibration allows his theory to work. There are many BPW/VE combos that will result in stoich operation, yes, but there is only one BPW/VE combo (when the VE is dialed in for 128 BLMs) that will result in the commanded AFR matching the actual (WB) AFR.