If the fuel pressure sensor were placed right before the rail, wouldn't a
decrease in reading (which should remain somewhat constant--only one
number to
remember) of this instrument yield the same results.

Not really, the pressure regulator will keep the fuel pressure constant
right up until the pump can no longer supply enough fuel for the engine, and
by then it is too late.  Once the fuel pressure starts to drop, the return
flow had already hit zero and your power will already be limited at best,
and the pump is in its final hour.  Still, with a second pump it usually
would not be a big deal.

I agree that one does need to understand the info from a given sensor.  But
I would give the benefit of the doubt to most everyone on this list.  If
someone has the ability to design and install their own auto conversion, he
has the ability to understand the info gleaned from the sensors he decided
to install.

It would seem that the

return flowage value depends on the throttle position and thus a lot of
calculation would be necessary (which you probably do as a matter of
course) to
really determine what was happening.

Yes and no.  The return flow does vary a little with throttle position
(higher map means higher fuel pressure so the pump is putting out slightly
less and of course the engine is using a higher percentage).  But I know
about what I should be seeing for a given MAP.  It varies from around 40 gph
at idle to just under 30 at max power.  When the fuel pump started to go, I
was seeing low 20's and slowly dropping...  flipping on the back up pump
fixed the problem.



I, personally have always found it easier to determine what a person is

eating by observing the intake of food rather than trying to figure it out
by a
fecal examination, although both would probably tell the same story.

If 40 gph is the baseline at idle, and it is showing 34 in flight... then I
know I am burning about 6 gph - give or take a smig.  That's not a hard
calculation at all.  If the sensor were in the inflow section, it would not
provide any information about how much fuel the engine was using, it would
also be less useful for my fuel management