I had a Problem yesterday with a new Filament, the DoubleDriveGear, wich draws the Filament into the Extruder, couldn´t grip it tight, so i had a very bad print, wich i stopped at that point.
So i remembered that there is a Screw behind the Extruder, wich controlls the tension of the Gear.
Plus it also has a Spring installed, if the Filament maybe is a little thicker than 1,75mm.
Now i had Problems with my regular BQ Filament too, it was the same.
Opened the Extruder to check if there are any Problems, there where none.
Re-installed the thing again and played a little around with the tension screw.
I fully closed it and then gone back about a half turn, it seems to work now, because the spring system works not with a fully closed screw, naturally.
But i want to know the original state in wich the Screw was, because i forgot to mark it with a Marker....