My 2.0 2004 TDCI did exactly the same thing and the Ford main dealer and an indie all reckoned on an internal failure but could not tell me what or where unless the engine underwent a full strip down.

FYI, after some research, it became apparent that a recon engine with 12 month warranty would cost in the region of £4K. The only guaranteed part was the block and head, all other components where to be swapped from the old engine to the new and then of course it might be wise to replace the clutch and possibly the DMF. Eventually ending up around the £6K mark.

The car being uneconomical was sold on for spares.