Hello, I'm having some trouble with my discovery 300 tdi. Firstly, I have very limited mechanical knowledge, secondly I'm skint! It started running poorly a few months ago, cutting out occasionally at junctions, since then it's got worse and worse, to the point it wasn't drivable. I changed the air and fuel filters a fortnight ago, and treated it to some diesel magic, which seemed to give it more pull, but the cutting out and slow starting was still there, so I changed the lift pump, which has made an enormous difference..... but it still cuts out and takes ages to start. No matter how much I try to bleed it at the filter, there is still lots of air in it, same at the injectors (incidentally, when injectors 1 or 2 are disconnected it doesn't run any different, when 3 or 4 are disconnected it knocks and splutters, don't know if that's relevant?) Please help!!