My solution for MK3S+ & MMU2S load to nozzle failure (for me at leat)  

My solution for MK3S+ & MMU2S load to nozzle failure (for me at leat)

Greetings all,

TL;DR - I solved my MK3S+/MMU2S filament loading issue by reprinting some of the nozzle parts. 

Like many of you all, I absolutely enjoy the great prints that the MMU2+ enables.  I'm equally frustrated by how finicky this system is.  I've spent 6 months perfecting my MMU2S set up only to have the dreaded "MMU failed to load" error crop up constantly.  In my case, the MMU successfully sent filament to the nozzle but the nozzle would simply grind the filament and not load the filament.  I could still use the Mk3S in 'single filament mode' by bypassing the MMU and manually loading the filament to the nozzle.  But, this was unsatisfactory to me. So, I scoured the forums and tried all the recommended solutions to no avail. Good news though - I managed to get my system working again after many, many hours of trial and error by trying something I hadn't seen recommended.

Here's what I did that might have helped (in no particular order):
- Cold pull (~5 times)
- Cleaned the MMU and nozzle bondtec gears
- Removed the stock buffer to remove friction
- Cut the 5 feeder PTFE tubes in half to reduce friction

Here are things that didn't help at all:
- Printed a modified extruder idler door
- Manually calibrated each of the PTFE tube lengths (which is not recommended for the Mk3S+, I know)
- Reflashed the printer and MMU firmware (same version)
- Completed a full printer recalibration
- Did a factory reset on the MMU twice

What ultimately worked?  I reprinted the stock extruder idler door, IR sensor cover, and IR sensor holder (chimney).  With these refreshed parts, the printer is back in action.

I hope this helps someone!

-Dan