Extruder not moving as material switches, blob of plastic results  

Extruder not moving as material switches, blob of plastic results

Hello, I recently finished adding the MMU2S to my i3 MK3.

When the printer tries to switch materials during or at the beginning of a print, the following things happen:

1) Extruder moves to lowest position (pretty much right on the print bed, where it would be for first layer)

2) Printer retracts current filament from nozzle to MMU2S.

3) MMU2S switches to new filament.

4) MMU2S pushes new filament down to extruder.

5) Extruder starts pushing out filament, but none of the axes move. A large blob of plastic builds up on the bottom of the extruder. Eventually, the extruder motor starts making a clicking sound as it continues trying to push the clogged filament. The MMU2S drive shaft also keeps going. The process continues until I manually reset the printer.

This results in filament dust building up on the bondtech gears in the extruder and MMU2S, and damage to the filament that causes further problems trying to push or retract it. I got it to successfully switch filaments once, so the first layer printed sucessfully. Everything seemed pretty much the same except that the extruder moved back and forth inside the wipe tower as the color was switched. I'm not really sure what I did differently, though.

I'm using Hatchbox ABS filament with the default ABS settings of 255C extruder temp/ 100C bed temp. I was trying to print the default lizard model with a green/transparent orange body and blue eyes. I created the GCode in Slic3r Prusa edition rather than using the premade GCode because I wanted to select the correct slots for the colors. I used 0.2mm layer height, 15% infill, brim, and a 70mm color switch wipe length.

I'm not using stealth mode, and I believe all my sensors are on/functional. Everything is properly calibrated, and it prints great with only one color. Any ideas?