The filament does not get chewed up and the and there hasn’t been anything wrong with the temperatures. (I installed my hot end on another printer, and it worked fine) The motor doesn’t seem to have enough strength to push the filament through, it is unable to strip the plastic off the filament. It twitches back and forth when it hits any resistance. The hot end is also completely clear of all plastic debris.
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If the same behavior is occurring with different motors, then the issue is likely not the motors. It could be a physical issue with your controller board such as power delivery or firmware. Also, wiring is always a possibility. “Jerky” sounds like a bad connection, so that may be a good place to start.
Try upping the current it is receiving.
It is NOT the stepper. They rarely fail, and your testing and subsequent posts imply it is not the stepper.
It is likely the wiring has gone bad. This is common for the stepper wires, which break inside from repeated same movement over and over.
Test a different wire, such as using the one from your y-axis. I’ll bet a dollar you will see the wire is bad.
PS If you have a ptfe liner, replace it now and then, it can cause these issues, but my money is still on the stepper wire.
A whole dollar? 
when steppers fail, it’s usually due to overheating which can warp the core where the windings are wrapped. This will cause the rotor to “hunt” for its index. In my case, the stepper would oscillate back and forth.
Update (Problem has been located):
- I switched the cables around, and there was no change.
- I switched the stepper drivers for the extruder and the z-axis, and the filament started extruding more smoothly than ever before!
- I had switched the drivers before, but with a different motor for the extruder. With the original motor for the printer, and the z-axis driver, it worked.
Thank you to everyone who helped, hopefully when the new driver gets here, there will be no more issues!
It actually was the drivers! I switched them out the first time, using the newer motor I had, and nothing different happened. When I switched to the motor that came with the printer, and then switched the drivers, it started extruding plastic perfectly. Thanks for the help.
I experienced something very similar, mine was harder to track down as it would only occur occasionally during prints. My printer would start out fine, then some time during the print my extruder would start jerking like you described. I thought it was temperature so I added active cooling, which did not help, I finally tracked it down to the plug on the end on the cable where it plugs into the stepper. The way mine is set up the flexing over time wore it out, and instead of trying to order a new one from china, and possibly having the issue again, I opened up the stepper and hard wired the cable, then built in a little strain relief using the case of the stepper itself. That was probably close to a year ago, and have not had an issue since. But in diagnosing this you need to be careful with the steppers being unplugged while being energized.
2 years later
I am having same issues. Filament wont feed. Stepper motor goes forward and back. Here what I have done. Swamped stepper motor cable - Cable was fine. Replaced complete extruder tip and tube - No difference. Changed Stepper motor - No Difference. Adjusted Stepper motor current - No difference Changed gear on feeder - No Difference. Changed guide wheel on extruder - No difference. Tried stepper with no filament in it or tension on the guide wheel - Motor still doing same thing. Reflash controller - No Difference. Replaced controller board - No difference. Reflashed new controller board - no difference .Checked power supply Voltages - All voltages rate where they should be. Scratched my head - no hair left. The only thing left is software. Same thing is happening in Cura and Mattercontrol. Have also reinstalled both. Help I am going crazy with this.
Does the original stepper have this issue plugged in somewhere else?
This still sounds like a cable issue.