I have no idea, but would hazard a guess its to do with power draw.
I know you can do compression test on modern trucks using just the diag computer, again I am assuming along the same lines as oscilloscope.
It is probably along the lines of it is seeing if they all have the same power draw.
yes.
From the starter motor I presume if that is the case, sounds a pretty unreliable method to me.
why? Was a main function on Bosch test equip.
I agree, too many possible variables to rely on load variation to compute compression pressures, I guess it would show no compression though.
As above.
I've never heard of it either, as I say, it might be OK as an all or nothing test for a broken crank, but I don't see it being possible to compute actual pressures from current variation, too many things could affect the readings from a weak battery to dodgy connections.
As above.
I think it is more of a comparitive test between cylinders, ie they are all pretty much the same so the problem is elsewhere.
With the diag laptop you can shut down individual cylinders whilst the truck is running, again I would assume for comparison purposes, ie shut down one cylinder and the others have to up their game to keep the thing running, the computer works out how much extra effort they are taking.
You can do some proper clever stuff these days, and we only really scratch the surface.
Yes.
J