Well... here we are again, happy as can be etc. Time for a roundup/update possibly?
FWIW, we have sliced open an OEM FIAT diesel fuel filter as well as a "quality" after market one.
No doubt the quality issues are important... and yes; it has to be worth getting OEM if possible. Going back to the original post though the real problem seems to rest with incomplete and misleading information on the part of suppliers... and ultimately; that tiny little fuel strainer nobody really seemed to know existed!
(1) For the record - contrary to what autodoc and others imply - that bit on the bottom
is just a water sensor and it
doesn't come with the filter! - Not even if the filter is actually supplied by autodoc! So, you do have to gently unscrew it and replace it equally gently on the new filter. - Carefully; it's only made of plastic!
(2) The main cause of the problem does seem to have been the very fine strainer which
on this particular version of the pump is in the inlet pipe! - And no, I still haven't figured out how to replace it; the replacement is still pinned to my notice board in the office! - Flushing this out, as described above, does seem to have cured the problem for the moment.
(3) BE CAREFUL of your part numbers if you decide to replace the regulator (or anything else); again misleading information is afoot - and it's almost impossible to work out what actually is a substitute for what else. There seem to be several variations on this type of diesel HP pump - some of which work one way, others work another; and even the experts (running classes in the subject) don't always seem to be getting it right!
(4) WINTER FUEL! - It's seems that even a slight freeze is enough to cause modern diesel to wax. I'm also being offered the theory that once waxed, the 'bio' component of pump blends does not simply 'melt' - but remains to some extent in a fine crystalline form. - This, is at least what has been suggested to me by an industrial chemist; and
is only a theory. - However, it is consistent with the practical/anecdotal evidence.
In this case waxed 'summer' diesel caused a Low Pressure 'lift' pump to be terminally damaged and appears to have clogged the inlet filter; which is something that might well have gone undiscovered. - Even my highly-reliable local garage say they would probably just replace the HP pump as they didn't know about the strainer. - They also related the tale of an Audi which had a similarly-damaged lift pump as the result of the same cold snap that killed mine!
Winter fuel blends seem to arrive very late and be withdrawn to early (already gone I'm led to understand!)... personally I believe it's now worth using an additional anti-wax additive
For the record... the car has just been for - and passed - an MOT. so, it would appear that all is well with emissions etc. And much of this story has been pointless tail-chasing. - Just for the avoidance of doubt; it appears there was some possible damage/wear to the regulator; so the replacement of that hasn't been a waste; but still...
If I'd only known to first check and clean out that unreachable strainer in the inlet pipe!