Ender 3 Pro won't extrude during print, but extrudes fine when not printing

Question

I have an Ender 3 Pro fitted with a CRTouch (I previously said it was a BLTouch but I was mistaken), and it was working fine until a while ago when suddenly it stopped extruding but only when actually printing.

I'm printing with PLA, but the issue happens with two different PLA filaments by different manufacturers, so I don't think the exact type matters.

The filament seems to be coming out of the nozzle perfectly fine in every situation except printing. I check this by raising the Z height high enough for me to see the nozzle, and then I use the menus to move the extruder 10 mm which results in a perfect desirable flow out of the nozzle. But then as soon as I'm printing, the extrusion either stops entirely or severely underextrudes. The gears that pushed the filament through just fine one second ago when I wasn't printing, suddenly start to slip and chew up the filament instead, when I am printing.

I have noticed when pulling the filament out of the printer completely after a failed print that the end has a twisted appearance (not blobs, but an appearance like the filament was being twisted in the hotend somehow. Spirals similar to a drill bit.)

I have done all of the following (things marked with two stars have been done multiple times):

• upgraded the Bowden tube
• used cleaning filament to clean the nozzle completely**
• used a needle to clean the nozzle out completely**
• done cold pulls with both the cleaning filament and my printing filament**
• printed at higher temperature (230 °C, where the filament in use said 200 °C minimum)**
• printed at a lower temperature (190 °C, where the filament in use said 190 °C minimum)**
• used a different filament that's brand new**
• probe Z offset (on firmware where it was apparently automatic)
• changed the probe z offset manually (on different firmware)
• adjusted the extruder gear spring clamp to be looser
• adjusted the extruder gear spring clamp to be tighter
• tried a different slicer (PrusaSlicer instead of Cura; also tried Creality print with the default settings for my printer, with and without the command to calibrate using the crtouch)
• opened up the fan shroud around the hot end and put it back together, which fixed some thermal runaways somehow but hasnt fixed this main issue
• changed to a build of marlin firmware found online for my specific printer setup, which changed the audible tone of my motors spinning but nothing else improved

All of this resulted in a good flow right up until I started actually printing, at which point, after a few layers, it stopped extruding properly again and then started extruding properly as soon as I canceled the print job, as evidenced by the filament oozing out suddenly as the print head moves into its default position.

This makes no sense to me, mechanically or otherwise. There is nothing I can tell that is different between printing and non-printing that would cause this issue, yet here we are. My prints are full of holes and stringy to an extreme degree they basically print as weak hole-filled cloth when they are meant to be solid objects.

Does anybody have an idea what might be causing the extruder to misbehave only when printing?

UPDATE: This is an ongoing issue, and I've edited the question with new information multiple times. Please check the last edited date and read carefully when answering or commenting. Thank you for the help.

Answer 1

It's unfortunate, but the only solution to my issue was to buy a better printer, after debugging for what feels like half a year at this point with absolutely no solution.

I concluded this was the only solution because, when I contacted a professional service to fix my Ender 3 Pro, they gave me a \$300 - $1200 estimate and even said that it would be better to just buy a bambu labs printer for a similar price.

direct quote from the repair service, typos and all:

Cost would be $300-1200 and I don’t relly recommend repairing them unless you just love the printer. The Enders are awful printers I would look at the bambu printers they seem to be ready to rock out of the box

So even though this answer is admittedly pretty bad in most cases, I felt it was worth the money after all this work trying to fix a badly designed Ender printer. And given the high ratings of the service I contacted, I trust their word.

Answer 2

I have solved the issue on my end. It is related to Z-offset. For some reason ever since I've upgraded to Professional Firmware this issue keeps happening. Basically, I have gone through 4 different Z-offset values in 3 weeks. I do not understand how the printer is changing somehow. The value is saved but needs updating all the time. I have gone from a setting of -2.30 to -2.38 to -2.40 to now -2.55. I was afraid I would be scratching the bed at this point but it's fine.

If you watch your printer doing the purge line when it then moves to the centre it's raising the hotend off the bed to start printing. My printer hasn't been moved and the bed is completely level. This makes no sense to me at all, that's why I'm leaning more toward it being a firmware issue.

Please try this yourself to see if it's the same for you and please let me know if it helps your situation. (P.S I did try to comment but it won't let me, but for some reason, I can post an answer, go figure)