Is it the extruder or mmu2 that drives filament into nozzle?
I've taken a bit of a break over frustrations post MK3S/MMU2S upgrade for a couple months. The last I tried I could not reliably get the IR sensor to calibrate despite following guidance tips and even printing new idler cover that has the switch lever. I finally just threw up my hands, downgraded firmware (the one just before the S upgrades went out ends in 1.05 I believe) and was using is solely for single color MK3 prints on any one of the 5 filament streams. It worked that way, for my needs, and I had no pressing need to multi-material (the novelty wore off via the frustrations). I figured I would return when I had more time and patience to work through the issues.
Now my wife just requested I print off 5 or so whistles for her elementary school summer school program. I left it the same way it was a couple of months ago and tried to print. I can load to the nozzle and get the filament to extrude just fine. I left the filament loaded to nozzle ready to go and started a print from SD right from the printer (not via Slicer or Octoprint) for simplicity. Despite having filament in the nozzle chamber it air prints. It was occasionally making clicking noises so I tuned the Z axis to give more clearance between the nozzle and bed. That did seem to help and I did get some feed thru but I needed to restart and the next time same issue. I cleaned debris from the drive gears in both MMU2S and MK3S and also FINDA. There does not appear to be any abnormal drag. Same issue over and over and I finally gave up.
I need help getting past this lack of feed issue. Thus my subject question. I think its the extruder or perhaps the G-code in that Whistle file is too outdated and it's not passing instructions to the printer or the filament sensor is reading 0 and refusing to feed. I just don't know. I'm tired of screwing with this hardware/software to get things to print.
RE: Is it the extruder or mmu2 that drives filament into nozzle?
Is this the whistle gcode that came with the printer or something you sliced? The pre-sliced gcode isn't going to work since it wasn't sliced for a MMU.
Don't let it cool with the filament in the extruder as this seems to lead to issues with jamming and (not your issue now) tool change failures.
In Settings use Move Axis to move the extruder to the middle of the X and Z planes. Disconnect the PTFE from the extruder, heat it up, and the use Move Axis to feed filament through. If that doesn't work, then you have a clog to deal with.
RE: Is it the extruder or mmu2 that drives filament into nozzle?
Yes it was the original I got with the MK3 a year or better ago. I'll scrounge up the file and run it with Slicer. Thanks for letting me know this was the issue.
RE: Is it the extruder or mmu2 that drives filament into nozzle?
That gcode was sliced for a printer without the MMU, don't use it with the MMU. Instead slice a new object for your configuration. I also suggest something that will be quick and easy (e.g. a small cube).
If you don't think you can trust your IR sensor I would disconnect the MMU (from the Rambo and extruder) and work things out as a plain printer (MK3S?). Once the IR sensor is working correctly through an entire print, then add the MMU back in and start debugging it's issues.
RE: Is it the extruder or mmu2 that drives filament into nozzle?
Also in addition of re-slicing gcode from MK3 to MMU2S you can use old gcode if you choose the "Load to nozzle" option. This allows you to first load a filament all the way to the hotend -similarly with loading on MK3S- and thus print "old" gcode.