if the person out there wants to get this problem sorted out. i did a number of test this week on mine 53 model. what this boils down to is when the pump starts whinning like a stuck pig it is starved of diesel, the test was i had two pumps and a bucket of diesel enough to cover the pump, when powered up the pump works fine .when you lift the pump up out of the diesel roughly half way up suspend it there.power it up then you will see that the fuel will go down before it starts to stabalise when fuel starts to come in at the bottom of the pump chamber so as the the fuel is used by the engine . the level also goes down sucking in air. so the problem is the pump cannot supply the correct pressure of four bar 58 psi, that is why some of you can not start because you need hydraulic pressure of liquid, getting back to what i did. it is on supply and demand .pump if it carnt suck it won't push it.
i took the plastic shroud off the pump and drilled eight holes around the bottom of it cleaned out put back it was quiet pressured up engine perfect,
i had this problem for some time thought it was injector seals in the head with air getting back to the pump , so before eny body thinks it;s this or that . please if there is eny good fitters to help others or if this helps that all right
i have now removed the return pipe off the filter and blocked off that fitting so that pipe goes straight back using the return on the pump so not to misread eny wrong results, so the pump will not pump air this is just to identify independent circumstances simple , the fuel reg i have change to a adjustable still the same pressure 4 bar so no more stupid changing of the reg ,if in the future with eny problems very quick to maintain
ps this one has pressure gauge on it so one can see whats happing thats how i like it