Sudden underextrusion on Ender3 I have printed a couple weeks perfectly fine with my Ender 3. Two weeks ago I changed the firmware but the settings were all fine and resulted in good prints.

Now, suddenly during a print the extruder motor started to under-extrude.

I thought "hey, could be the file" and used a test file that printed well two weeks ago: Under-extrusion, barely a line.

I looked at the extruder, no filament grinding, no clicking from lost steps or moving against pressure. The Bowden tube is firmly seated though.

I measured what is coming out: instead of 50&nbsp;mm I ordered to push into the hotend got 28.7&nbsp;mm. So I went and looked at the steps/mm, which is 93, exactly what it is also on the TronXY X1, which uses pretty much the same extruder setup but for a different style, same sized gear.

I cleaned out the nozzle nevertheless, but that didn't change the results.

What might be wrong and how can I fix it?!

Edit:


Touching the filament while I was printing a freshly sliced test, I realized it DID lose steps, just the filament did slip back (almost) quietly. Pressing a finger on the filament made me able to feel the shiver in it.
Inspecting what was printed showed, that the nozzle had migrated against the print platform a little over the weeks.
A close inspection of what happened when printing the first layer resulted in this:


The missing steps on the new print came from the nozzle scraping too close to the print surface, which lead to no first layer
Readjusting the Z-axis end stop, which had moved down, resulted in no more lost steps, but the print not sticking for the first test.
Releveling the bed and making sure the bar was parallel to the bed resulted in a perfect first layer.
Lost steps and under-extrusion could not be replicated after 48 hours of rest for the printer.


I have no idea why the print had failed due to under-extrusion during the print, but apparently, my immediate tests were flawed enough to not detect the first layer height resulting in getting almost no extrusion. This I mistook for massive under-extrusion, making me believe something else was at fault.