I had a starting problem with my fiesta1.4tdci. The motor cranked and ran for about 2-3 seconds and then stopped. This happened random, however almost never when the fuel tank was completely full. I searched a longtime for the possible cause (glowplugs, fuelfilter, fuelinjectors) without finding the solution.
A few months ago I cleaned out the fuel-sender-unit and the fuel-line (running from the fuel-sender-unit to the fuelfilter) with compressed air. That solved the starting problem. Since then the car starts again without any problem.
The removal of the fuel-sender-unit is a bit tricky. I cut a circular hole just above the unit with a pair of sheet-metal shears. Otherwise you have to remove the fuel tank completely, what is quite difficult to do without a lift bridge.