The fuel accumulator, acts as a reverse flow check valve, but is more of a reverse pressure regulator. It allows the fuel system to hold pressure, from the delivery side (tank and pumps) and insures quick start ups, by keeping the fuel pressure up, even when the pumps have been off for many hours. If the accumulator is letting go, (leaking down) while driving, the end result is a lowered fuel pump pressure to the fuel distributor and its pressure regulator. The only way to see this, is to drive the car and monitor the fuel pump pressure remotely via a gauge brought into the car. I do suggest a helper friend to watch the gauge, as not to be destracting while you are driving. You can block the return line from the accumulator, but you run the risk of introducing contamination into your fuel system, if you dont do it in surgically clean way. If you havent already checked your ignition coil out, do so, you might be suffering from this power loss due to ignition break down under compression from a weak coil....Check the color of your spark....!!!! Any unusual noise from the pumps can be traced first to a clogged pick up screen in your tank, It makes a sorta slurping sucking noise, like when you pull soda from a straw in an almost empty can, or, a squishing sound, (over pressure) from trying to suction through a very clogged filter. Or, maybe the motors armature bushings in the pump are shot, rare until around 250,000 miles. Usually poor power problems stemming from a clogged fuel filter, lessens when you add more fuel into the tank. The extra fuel now available, via gravity, helps push the fuel better into the pump system.