This is a problem with a Sierra 1.8td. I know it's a dog of an engine but..
I have tried everything to solve this problem to no avail. First off the car starts fine, however after about 5 /10 minutes air starts appearing in the clear line before the fuel filter. I installed a new fuel line between the tank and the filter. And also I've check the fixed line that runs from the fuel tank. When you run the car the primer bulb immediately before the filter first loses pressure and then the filter itself runs out of fuel and the car stalls, its as if the injection pump is demanding more fuel than can be provided. I've tried everything any suggestions would be appreciated.

 

I assume you have ruled out a split diaphragm in the filter head, if it's the one I'm thinking of it's very very common, about £15 a new one.
tabetha