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Hi,

i have the problem that after each retract, the material does not extrude imediatly. This results in 2-4mm gaps in the infill.
Like it is retracting 6.8mm (current setting), but extruding (after retract) only 4mm.

I have tried to reduce the retract speed from 110 to 55mm/s, but it did not change the problem.

I used ABS with 225°C temp. Overall print quality is ok.

Is there anything that can be done?

I assume you are using an EZSTRUDER? And the stock Hotend? Which slicer and how have you configured it?
Some slicers you specify the ammount of filament to push after the retract and some the ammount of extra filament to push.

The odds are you are loosing steps during the retract, what you need to do is play wyche the settings until this stop s happening.
I would start dropping retracts to 5mm at 20mm/s, that will cause other issues, but you're just trying to establish the point where the problem goes away, you then increase the speed until it comes back, you can then try increasing the current to the extruder stepper to see if that resolves it. Then mess with retract length etc etc.
The idea is the same as any trouble shooting or tuning, establish a working baseline, then tweak one thing at a time.