Fuel pressure is low replace the filter and check again. The only other possible problem is a intake gasket which could cause both banks to be lean. If it was only the bank that cylinder #4 is on I'd thing a clogged injector.
Fuel Pressure Pressure 1 (PSI) Pressure 2 (PSI) Pressure 3 (PSI) Range Note Range Note Range Note 60.0 - 66.0 Y131 50.0 - 63.0 Y132 66.0 Y133 Y131: System pressure with ignition on (PSI). Y132: System pressure while idling (PSI). Y133: Fuel pump pressure (PSI) with return line briefly restricted.