Why would my extruder remove the filament all the way out after prints? [Ender 3 v2]

Question

Background

I bought an Ender 3 v2 printer, everything has been working fine, been experimenting with harder and higher temperature filaments like different variations of PLA and PETG.

Original extruder would bite the filament too hard sometimes and snap it, if it's loose it would grind it, filling its teeth with material that needs to be cleaned out.

I bought a BMG clone (TriangleLab) extruder and set it up according to BondTech instructions but without having to invert the stepper motor rotation and set E-Steps to 419, which seems to be printing fine.

It's still using the stock hotend but with 0.6 mm hardened steel nozzle. I do have BLTouch add-on and I'm using firmware compiled from tip of bugfix-2.0.x branch of Marlin with stock Creality v4.2.2 board. Firmware Configuration modifications were done to accommodate BLTouch alone.

Problem

I have to manually heat the nozzle and manually extrude about 200-250 mm from LCD menu, otherwise once print starts, no material will come out.

I checked the bowden tube with a torchlight since it's translucent using a black filament to print and noticed that after machine is stopped (from menu or after print ends), extruder will pull the filament almost all the way out while pulling up Z axis to clear some height, requiring me to manually extrude before next print so tube won't be empty. Previously with stock extruder I didn't have to do anything, the initial print on left hand side of bed or skirt print would take care of putting it back in location.

I've been googling and looking at Cura and Firmware (configuration.h) for a while now but I couldn't figure out why this is happening.

This is my End code in Cura. I do suspect 3rd line has something to do with it but I don't understand what that means.

G91 ;Relative positioning
G1 E-2 F2700 ;Retract a bit
G1 E-2 Z0.2 F2400 ;Retract and raise Z
G1 X5 Y5 F3000 ;Wipe out
G1 Z10 ;Raise Z more
G90 ;Absolute positioning

G1 X0 Y{machine_depth} ;Present print
M106 S0 ;Turn-off fan
M104 S0 ;Turn-off hotend
M140 S0 ;Turn-off bed

M84 X Y E ;Disable all steppers but Z

M300 S440 P200
M300 S660 P250
M300 S880 P300

Retraction settings are stock settings in Cura, haven't touched them.

The Configuration.h file is found here, the Configuration_adv.h file is found here.

Update: This happened again with Benchy print but about 4 cm unlike previously, half of the skirt print failed but actual print was OK. Below is last part of print Gcode. End code isn't different from Cura settings printer end code.

G1 X105.151 Y113.199 E313.92164
G0 F7200 X105.155 Y112.539
;TIME_ELAPSED:3369.503317
G1 F3000 E307.42164
M140 S0
M107
G91 ;Relative positioning
G1 E-2 F2700 ;Retract a bit
G1 E-2 Z0.2 F2400 ;Retract and raise Z
G1 X5 Y5 F3000 ;Wipe out
G1 Z10 ;Raise Z more
G90 ;Absolute positionning

G1 X0 Y220 ;Present print
M106 S0 ;Turn-off fan
M104 S0 ;Turn-off hotend
M140 S0 ;Turn-off bed

M84 X Y E ;Disable all steppers but Z

M300 S440 P200
M300 S660 P250
M300 S880 P300
M82 ;absolute extrusion mode
M104 S0
;End of Gcode
;SETTING_3 {"extruder_quality": ["[general]\\nversion = 4\\nname = Ideagen Nozzl
;SETTING_3 e-0.6 #3\\ndefinition = creality_ender3pro\\n\\n[metadata]\\ntype = q
;SETTING_3 uality_changes\\nquality_type = standard\\nposition = 0\\nsetting_ver
;SETTING_3 sion = 15\\nintent_category = default\\n\\n[values]\\nfill_outline_ga
;SETTING_3 ps = True\\ninfill_overlap = 10\\ninfill_sparse_density = 40\\ninitia
;SETTING_3 l_layer_line_width_factor = 120\\nironing_only_highest_layer = True\\
;SETTING_3 nmaterial_flow = 92.5\\nmaterial_print_temperature = 210\\nretraction
;SETTING_3 _count_max = 10\\nretraction_retract_speed = 50\\nspeed_print = 60\\n
;SETTING_3 speed_travel = 120.0\\nsupport_infill_rate = 5\\ntop_bottom_thickness
;SETTING_3  = 1.05\\ntop_thickness = 1.05\\nwall_thickness = 1.2\\nzig_zaggify_i
;SETTING_3 nfill = True\\n\\n"], "global_quality": "[general]\\nversion = 4\\nna
;SETTING_3 me = Ideagen Nozzle-0.6 #3\\ndefinition = creality_ender3pro\\n\\n[me
;SETTING_3 tadata]\\ntype = quality_changes\\nquality_type = standard\\nsetting_
;SETTING_3 version = 15\\n\\n[values]\\nlayer_height = 0.35\\nlayer_height_0 = 0
;SETTING_3 .4\\nretraction_combing = infill\\n\\n"}

Answer 1

As mentioned in the comments, extrusion stopped working altogether at some point halfway through a Benchy print. Once I had opened compressing lever of BMG clone extruder, I observed that gears were loose, after disassembling the extruder noticed that both extruder side and stepper motor side gears were also loosened at hex head screw keys which were keeping them in place. I ordered a thread locker to address that at another time, seems like vibrations due to constant retractions loosened them.

After tightening and reassembling, issue is not bad to the point prints would fail to start, however filament is not primed enough, so some of the skirt print will be blank.

I also added this with 608Z bearings for supporting the smooth movement of spool. Turns out 608 bearings are widely available almost everywhere, roller skates and skateboards use them, so there is a good chance your local sports shop will have it, too.

I installed Octoprint on my laptop to work around this issue as below:

G92 E0 ; Set Extruder position to 0
G1 E100 F200 ; Extrude 100 mm slowly. This is to make sure hotend is not empty and material flow is consistent, i.e. adjust temperature if necessary.

Only then I start my prints.

I learnt that using E<integer> to extrude and E-<integer> retract, I can replace filament too, by using big enough numbers like 350 mm, so I don't have to fiddle with compression lever or its adjustments anymore.

Update: I found more mechanical problems. This issue is not software related. Please see useful advice in comments regarding retraction/priming as an improvement if not solution to this problem.