My 2.7L CRD Mercedes 5 cyl. cranks but won't start in the mornings. Garage says it looses it's fuel pressure over night??

This sounds very familiar. For some time now the fuel hose, on my 2003 Grand Cherokee 2.7L CRD ( Mercedes engine), from the top of the fuel filter to the low pressure pump on the front of the engine has been gathering air from somewhere…(usually overnight). Cranking the engine for 30seconds or so sometimes re-primes the system and the engine will start but prolonging the cranking also runs down the battery! The obvious difficulty is that you cannot see any diesel fuel leaks and this strongly suggests that air is leaking into the pipe leading to the low pressure pump. This is the pump and hose combination that draws (sucks) fuel through the fuel filter from the fuel tank. (There is no electric pump in or near the fuel tank.) To prove that it is an absence of fuel in the low pressure area try drawing fuel through the priming socket that sits on the top of the engine alongside the CRD rail. The low pressure pump should now prime the high pressure pump and the fuel pressure sensor should be able to initiate an engine start. If the engine fires then you have identified the problem as an absence of fuel in the hose from the fuel filter. The question now is: How do you identify where the air is getting in? A likely suspect is any one of the tiny “O” ring seals that forms part of the preformed Mercedes fuel hoses which are not cheap and very likely to break when you try to remove the hose just to examine the O rings !!! Bite the bullet and replace the entire low pressure hose assembly (including the primer port if that has been used a few times) If the problem persists or changing the hose does not cure the problem then maybe the fuel pressure sensor has failed as well.