Odd issue, resolved. Might help someone else  

Odd issue, resolved. Might help someone else

I'd been printing away for over a year using the MMU in single mode, but using all the five filament slots since I use many colors with lot's of manual filament changes.

I ran into an odd loading problem that took quite a while to diagnose, so I thought that I'd share. 

I had some minor loading issues lately but all of a sudden nothing was loading correctly.  When the filament was being loaded I was getting a grinding issue at the hot end.  Did all the usual checks, clean sharp filament head and no grinding spots, extruder not clogged, Sensor working perfectly, extruder gears turning and trying to grab the filament but nothing moved.  I could manually insert the filament and it would feed properly.  MMU loading/unloading actions all working correctly.

During loading, the MMU would back the filament out after some time and try loading again, but each time the filament would not pass the extruder.

After much, much head scratching I found that the MMU was not fully releasing the filament when it got to the extruder and therefore the extruder was fighting the MMU for filament ownership!  The MMU stopped feeding the filament at the right time but did not release the pressure on it. This was all happening on slot one.  Turned out that there was a tiny bit of filament head stuck behind slot 4 that somehow kept the pressure of the roller on slot 1.  This tiny bit of filament did not look like it was interfering with anything but removing it cleared everything up.  Really surprised me since nothing was binding and all motions that I had previously tried with the MMU worked fine.

Just thought that I'd pass this on since the real problem/solution was at the other end of the machine from where the problem seemed to be occurring.

Teamwork,

Steve