Ford Focus TDCI cuts out

[SteveyT]

Hi I have a focus 1.8tdci on an 03 plate with 89000 miles. I have a problem which is really baffling. Car cuts out and will not restart. When this happens the fuel filter is half empty. Incidentally no stored faults on diagnostics. I have removed the fuel tank and cleaned it out including the swill chamber, put air line on steel pipe to filter and renewed plastic pipe to filter. Fitted a second new fuel filter on the off chance the first was faulty and put in brand new fuel.  The same thing is happening again car starts, will run for a little while, then cuts out, so if I remove the pipes and top up filter it will start up. Hs anyone any ideas what the problem could be? Many thanks 

[TomsFocus]

Air leak on one of the pipes, the filter should always be full of diesel.