I had the same problem with a Benz I used to own. I was told by my dealer that there is a relay located on the gas tank that holds fuel pressure in the line when the vehicle is turned off! This relay often goes bad and the fuel returns to the tank, letting air into the line. When you pump the pedal you are getting fuel that hasn't drained back to the tank ( as a reslult of the bad relay) and is left up top ! Thats why the car cranks.
1957 Dodge D100
1967 VW Microbus 21 Window
2004 Beach cruiser bicycle
"It cannot be emphasized too strongly or too often that this great nation was founded not by religionists, but by Christians; not on religion, but on the Gospel of Jesus Christ. For that reason alone, people of other faiths have been afforded freedom of worship here." Patrick Henry 1776