I had a similar fuel problem on my old 4/4. The pump failed due to c**p from the tank.
I flushed the tank, new pump with a filter to protect it, flushed the fuel pipes, new flexible pipes,new pre engine filter. Solved! The lack of tank to pump filter was the issue. The engine side filter protected the injectors.
Car was 20 years old when bought. Maybe a sensible procedure for older cars anyway?

Plus Four MY23 Furka Rouge