Had this on a couple of engines,low fuel pressure codes stored,fault found after making up a home made injector leak back tester with BIG resevoirs (juice bottles).

Anyway,started and ran them until the fuel rail pressure started to fall (Planet),once the rail pressure droped under 180 bar engine would stall and not restart until cold,this is when the home made tool comes in,leak back from all 4 injectors normal,once the pressure began to drop one return bottle started filling at an in creasing rate.

non start cranking test showed one injector was leaking back at a hell of a rate,until the engine cooled then normal.

as it was a taxi the brief was "just fix please",injector exchanged at dealer and vehicle ran flawlessly,best guess,and it is a guess as I didn't have the original for more testing was that some form of micro fracture in the injector that only open up at temperature and then closed when cool.

So injector leakack test while monitoring the fuel rail live pressure,oh and the reason for the big bottles was one car only did this at 15 and a half mins' running time