Poor fuel pressure

I have a 2000 Ford Taurus ohv. The car is reading
codes that both banks are too rich and that there's
a secondary fuel pump circuit issue. However,
while in drive while accelerating from a stop, the
car seems to be losing fuel pressure and will take
off slowly and eventually get up to speed.  While a
fuel pressure gauge is hooked up to the fuel
injector rail, with the key on ignite, it says there is
absolutely no fuel pressure. Once the car starts,
the pressure will slowly build up to a a little under
20 psi. I believe the normal amount of pressure for
this car is around 40 to 50 psi. The car will also rev
up just fine sitting, but while driving is when it loses
power.