Ford Repair: Ranger brakes, wheel abs, abs brake

Question
93 Ranger 4by4 4.0 auto. For a while after it sat for a couple weeks.The first time I drove it I'd have to pump up the brakes then it would be fine till I parked it again.
It started leaking from the left rear line.I fixed that and bled all 4 brakes.With the engine off the brakes felt normal(the pedal barely pushes down)Start the engine and the pedal goes to the floor.So I replaced the master cylinder and bled all 4 brakes again. With the engine off the pedal barely goes down,start the engine and the pedal goes to the floor and won't pump up.There are no leaks but the vacumn chamber between the master cylinder and the fire wall is realy rusted on the underside but it seems to hold vacumn.Could this be my problem?

Answer
Hopefully you used new parts, most of the reman or rebuilt master cylinders are junk. If this truck has 4 wheel ABS, it will need an ABS brake bleed procedure and may require a scanner.

If it has rear wheel ABS, and there are no leaks, could be a stuck RABS valve.