Trouble starting - some kind of fuel problem?

[greasyrob]

My E350 is killing me - there's always something going on with it. I did convert it to run on vegetable oil but my troubles seem to be unrelated since I haven't switched to VO in a few days - only diesel was used - and I still had the trouble yesterday morning.

Basically, it cranks fine but the only way I can get it going is to disconnect the return line and try cranking it. This usually works, which I would think means that there's some kind of obstruction in the return. I've disconnected the return line up at the engine and that usually works. Yesterday it didn't, so I disconnected it where it enters the fuel switch (this is a 2 tank van). That worked like a charm. Does anyone know what I need to do? I've tried with the fuel switch both ways so I don't imagine it's a problem between the fuel switch and the tanks. My only guess is that there's some kind of clog that is only allowed to work itself out when the line is open on the other end (as opposed to going into the tank). In case it matters, fuel was pretty low in both tanks.

Thanks a lot for any help..
Rob

1991 Ford E-350 7.3l IDI

[OkieGringo]

The problem might be that the valve for the return to the tanks is not opening. On my 87, the valve is stuck so that only the rear tank gets return fuel even if the front tank is being used. OkieG