<... fuel pressure would begin dropping, along with power, and exhaust temps
would rise ...>
That'd be my guess too.  So an engine monitor showing both pump pressures (if
parallel) would show a decay in pressure.  I'd be comfortable using both pumps
for TO and landing, switching them enroute one to the other.  Matter of fact,
didn't I decide last spring to design my fuel system to have left pump draw
from left wing, right pump from right wing anyway?
Yes I did :o)  Having a senior moment here ... Jim S.

Mark Steitle wrote:

>  Does anyone know with any accuracy how fuel pumps fail?  I
> >doubt they fail catastrophically.  I suspect they fail by degrees
> >(probably very gradually as the poorly maintained filter clogs up).
>
> I went through this scenario a few years ago on my 88 Chevrolet p/u with
> EFI.  The engine warning light would come on when climbing grades.  Also,
> power would drop off significantly.  When reading codes it indicated too
> lean a/f mixture.  (I assume this was due to very low fuel
> pressure).  Things returned to normal once the new fuel pump was
> installed.  So, my guess is that the fuel pressure would begin dropping,
> along with power, and exhaust temps would rise.  Pulling back on the
> throttle should help some.