erm not sure. The RAC guy said it was the pump by the fuel tank, he said they are a common fault and often goes out to W202 cdi's with this prob.... He undid a pipe going into the injector pump and turned the car and no fuel passed through and that was his deciding view.
well basically I ran out of fuel, put 3 gallons of diesel in, turned it over until the battery went dead. Charged the battery , turned it over and over again, and gave up, rang RAC he came out. he tried turning it over a few times, he instantly said it doesnt sound like it had ran out of fuel. He took the engine cover off, he put some node on some wire(sorry for the vagueness, but I was just watching and not asking questions) that he disconnected and turned the car over and node was lighting up(I presume something to do with heater plugs). and all he said was " well its not that" .
He then he then proceeded to try the pipe which fed the injector pump to which he did explain that fuel would not come out the pipe if the fuel pump by the fuel tank is screwed. No fuel did come out the end and thats when he decided that the 'high pressure fuel pump' (is that right) is knakard.