yes the trusty pumpa diesel tdi. bit of an issue with these at the moment im afraid.
there is a problem with the seals failing in the tandem pump which helps pump fuel to the injectors in the cylinder head.
what happens is the seals fail and - cross contaminates fuel and oil.
the oil gets into the fuel system - and does 2 things.
it dumps all this crap in the tank and the fuel filter.
and then it attacks the oils seals on the fuel injectors.
the injectors begin to lose pressure passed the seals and cause lumpiness and usually at high throttle demand - it just flat lines - guttless.
what i suggest first is - cheapest way to check first -
remove fuel filter and pour into a clear container. - if its black - i mean it well be really black - then this confirms my suspisions.
first job to do - fit new fuel filter.
2nd job - fit full set of injector seal kits
3rd job - fit new tandem pump assembly
4th job - access fuel pump in the tank - through the boot floor - remove 3 screws of cover - and then you well see the pump screw top. remove the fuel pipes and electrical connector first.
then hit the screw top anti - clock wise with a blunt screw driver or similar and a hammer.
remove fuel pump assembly.
discard all the fuel from this assembly. and try to clean the pump assembly as best you can - or you will have to renew this also.
pump out all the fuel from the tank - and discard it. its contaminated - you need to get rid of it out of your cars system.
get loads and loads of rags or boxes of bounty kitchen towel !
wipe out all the fuel tank - you will see that it goes from what you thought should have been black now change to grey / white tank lining. clean it out as much as you can - stick your arm right in there.
well i hope this helps you out.
i know its not particularly good news but im sure it will help you.
if you are satisfied with my help - please accept.
any feedback / bonus is greatly appreciated also.