Here is the D/O of your fuel pumping system. MAybe it will give you some ideas. I dont know what you have tried other than a pressure regulator. Have you checked the fuel filters for clogging? Replaced or tested either fuel pump?
1985 - 87 4-140 EFI EXCEPT AEROSTAR & V8-302 EFI, EARLY 1986 AEROSTAR 4-140 EFI, 1986 - 87 V6-177 & 1987 6-300
The electric fuel pump system consists of two fuel pumps: a low pressure boost pump mounted in the fuel tank, and a high pressure fuel pump mounted on the frame rail. The low pressure pump is located with its inlets at the bottom of an internal sump in the fuel tank. This design provides for satisfactory fuel pump operation during extreme vehicle maneuvers and steep vehicle attitudes with low tank fill levels.
The low pressure electric fuel pump, Fig. 6, is used to provide pressurized fuel to the inlet of the high pressure pump and helps prevent noise and heating problems. The inlet of the low pressure fuel pump has a nylon filter on it to prevent dirt and other particulate matter from entering the system. Some vehicles use an external resistor in the low pressure pump circuit to reduce operating voltage to 11 volts, Figs. 7 and 8.
The externally mounted high pressure fuel pump, Fig. 9, is capable of supplying 15.9 gallons of fuel per hour at a working pressure of 39 psi. The pump has an internal pressure relief valve to provide over-pressure protection in the event the fuel flow becomes restricted. Over-pressure is restricted to 123 psi and reduced fuel flow will result. The system pressure is controlled by a pressure regulator on the engine.
Sunday, August 13th, 2006 AT 7:27 PM