check for gas in the engine oil, Ripped diaphragm in fuel pressure regulator and "do" this.
ripped "d" can lead to pumps running, yet low pressure to the rail and most getting back to the tank via return line, but some ends up in the oil via cylinders leaking.
1986 F-150 Flareside 4x4, 351, 4-v, ZF5 speed. AC, Cruise, Tilt, Slider, Digital clock, Radio, Lariat seat, Pwr doors/locks