Try an alternative fuel source. Get a one litre pop bottle. Run clear vinyl hose, the same size as fuel hose into the bottle. (you can buy the hose at most hardware stores.) Hook one hose up the inlet of the clear fuel filter and hook the other up in place of the return hose on top of the large fuel filter. Start the engine. This will tell you three things. 1. It will tell you if the fuel lift pump is working. If the fuel circulates thru the pop bottle, the lift pump is working. 2. If it runs ok this way, the problem is in the lines or fuel tank. 3. If you see a lot of air in the circulating fuel, you're probably sucking air thru the primer pump.
It's a simple, inexpensive test that can help you narrow the problem down significantly.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13