What's causing this problem ?

[0nailime]

I have the pro w since September, i managed to make it work very good using simplify 3d, i was satisfied with my prints, the only issues not resolved was a bit of ringing, but from last month i had terrible results.
I managed to clean the nozzle, calibrated the extruder, tried almost everything with print speed, retraction, wall size, heated bed calibration. I don't really know, i used to have this problem for a period due to filament slipping in the feeder, but now the extruder is calibrated, so the feeder is good and the nozzle is new and not clogged.

[William]

I think you should check the temp,retract,filament diameter and nozzle diameter in slice software at first.

[0nailime]

I have all set up correctly, i use simplify 3D but also used repetier host with success before, nozzle is 0.3, using sunlu pla+ filament 1,75mm, i tried from 190 to 215 in steps of 5 degrees, same results, also tried different speeds of retraction, having troubles also in vase mode. I switched also filament with a black pla from geetech, even worse results, the strange things is that i managed to make very good prints before. I even changed extruder and nozzle with a new spare one. This is driving me crazy

[0nailime]

Forgot to mention i have also checked belt tension and all the screw, i don't really know

[William]

Maybe you can check these:
1.Check the spring of the feeder
Try to replace it
2.Try to increase the vref of the A4988
3.Check the cooling fan broken or not

The FAQ of the i3:
viewtopic.php?f=109&t=61933