Right, further to my wont start problems, a diagnostic expert has narrowed it down to fuel regulators. So on my Delphi fuel pump there are two sensors/regulators/valves, a big fat one down the bottom(that screws in using big spanner flats) and a thinner one up top with two 4mm hex bolts holding it in, I can find info about the fat one (its a fuel control valve).Anybody know what the top one is?suction valve?pressure sensor?(as opposed to valve)
countless google searches have found nothing

its the sensor top right in this photo, thats from the haynes manual which doesn't actually say what it is. It does say the manufacturer doesn't recommend remove of sensors but at 700 quid for a new pump i'l do what I can first (and why are the sensors available? Ive replaced the fat one at the bottom-which is a Pressure Control Valve)