Prusa MK3S extreme stringing all of a sudden

Issue

Prusa MK3S extreme stringing. Started out of nowhere on the same print files (gcode) which had previously been successful, with minimal stringing.
The Prusa MK3S extreme stringing issue is occurring using same GCODE and same filament (even same spool) of successful prints on sister printers (same kind) of same model and age. This indicates it's not an issue with:
  • wet filament
  • room humidity
  • print settings
  • temperature settings
Prusa MK3S extreme stringing

Environment

Prusa i3 MK3S
PrusaSlicer
Typical filament: Filacube PLA 2
  • 220° nozzle first layer
  • 210° nozzle subsequent layers
  • 60° bed first layer
  • 50° bed subsequent layers
Typical print settings:
  • 0.2mm layer height
  • Retraction 2mm length, 40mm/s
  • 0 Z-hop
  • Print fan at 100 after first layer
  • Speed:
    • Perimeter 45mm/s
    • Small perimeter 25mm/s
    • External 25mm/s
    • Infill 80mm/s
    • Travel 180mm/s

Troubleshooting steps

  • Added
    • Sunlu filament dryer box, drying filament before and during each print. No difference.
  • Replaced:
    • Nozzle
    • Extruder motor
    • Bondtech gears
    • PTFE tube
    • Nozzle
    • Print fan
    • Fan shroud
    • Checked/calibrated:
    • PID tuning (on machine)
    • Lin. Correction (extruder)
    • Belt tension (well within range, same as successful machines)
    • Heater block temp (IR thermometer)
    • Filament (different spool, fresh out of package and dried, same temperature settings as other machines' successful prints)
    • Spool humidity (dry, same as others)
    • Print settings (same as others)
  • None of the above-noted replacements made any difference.
Remaining options:
  • Hotend assembly
  • Thermistor wire
  • Heater wire
  • Compare width of old and new nozzle
  • Genuine E3D nozzle
  • Look with a flashlight between the top of your heater block and the bottoM of the heat sink. You should be able to see the shiny metal of the heatbreak between them. If there’s any filament in there, your hotend is leaking and you need to clean it out and reseat the nozzle per Prusa instructions.

Resolution

After all of that, I simply replaced the nozzle (again), this time ensuring it was a genuine E3D nozzle. Installed and took time to ensure it was seated properly. 

Then, I ran a manual PID tuning with 8 cycles rather than the on-board PID tuning (5 cycles). 

Original values:

Recv: echo:PID settings: Recv: echo: M301 P16.21 I1.30 D50.49

 

Following manual PID tuning with 8 cycles: 

Recv:  Kp: 18.70
Recv: Ki: 1.58
Recv: Kd: 55.14

 

This resolved the issue and I was able to print these hands with no issue!

Prusa MK3S extreme stringing

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