FF Finder - Print quality suddenly worse after failed print

A few weeks ago I was doing a large print wich failed halfway trough as the printer stoped extruding. The print had bad surface finish and a lot of stringing, problems I have not experienced before.

After cleaning the nozzle it was extruding again and I could print, but the surface quality on vertical surfaces was not as good as before. I tried cleaning the nozzle again, but no change. I concluded the nozzle was probably worn out or gunked up with something I couldn't get out, so I replaced it with a new Prima Creator nozzle. This had no detectable effect on the print quality.

I have also cleaned the gear and idler in the extruder and switched to a new spool of filament. Still no detectable effect on the print quality. (I also cleaned and lubricated bearing all rods and Z-axis lead screw, not surprisingly, no effect.)

One of the test prints was printed from the printers memory before and after the problem started, so I can rule out slicer settings.

Any ideas what could be causing this? Maybe the PTFE tube or some other part of the extruder?


Attachment 11950Attachment 11951Attachment 11952Attachment 11953

I tried one more thing: I suspected the problem might have something to do with print temperature, but printing at 210 and 230 degrees resulted in prints identical to those printed at 220. (Using Flashforge PLA).

I noticed my pictures got scaled down enough to make it hard to see the problem clearly, so I have uploaded higher resolution images:

Under microscope, notice "bubbles".
Before and after
First print to fail 1
First print to fail 2

To summarize there are two problems:
1. Uneven layers, similar to Z-wobble, except it's random, not regular.
2. Small "blobs", which I think are typical of wet filament, but I have tried with known dry filament (PLA and PETG) and got the same result.

Since my last post I have replaced the nozzle and PTFE tube. This resultet in no difference in print quality.

Any suggestions?

well on the before print it looks like you are starting all layers from the same point - hence the z 'ridge'.
in the after looks more like random start points.
Also possible retraction between layers might have been switched off. That could cause the same issue.