My wife has a ford fusion 1.4dci 2007.It cost 3.5k and has had constant problems since we bought it.One suspension spring broke,the engine judders occasionally at any speed,we were told it was old fuel but 2yrs later and a couple tanks of super diesel and it is still doin it.It has had injector seals replaced inlet mamifold replaced with new seals,gaskets,map sensor pipe replaced,egr valve replaced and egr cooler as engine diagnostics showed this as the problem.We have shelled out over a grand more on it in 2 yrs and it still runs stuttering occasionally.I bought one of the same but a 2008 and mine is doin the same now.Ive just about had enough of both of these cars.Has anyone got a clue what the problem could be,a mate mentioned an engine management chip upgrade,another mentioned redex and another mentioned the scrapyard😄 any help would be much appreciated.

redex is as good as an ash tray on a motorbike imo. Forte diesel treatment has been good to me in the past....

however, for starters you never mentioned the fuel filter, i think replacement interval is 37k miles but they can cause problems.

Super diesel i found makes no difference to my fusion or my mk4 astra 1.7 DTI - heard horror stories using supermarket fuel but i have had no problems whatsoever.

Next suggestion from me is possibly an injector issue.

These cars shouldn't require an engine management chip upgrade (mapping) ? to run as a factory standard car.

fuel filter or injector imo / over internet diagnosis.