Motor or motor controller
 

What is a good way to determine if motor or motor controller is causing the symptom of motor just stuttering/jerking for a few seconds then nothing. Can I substitute 3 resistors for motor and expect pulses to appear across resistors when
applying throttle?

Could be a loss connector. It is probably the battery. If the battery is not charging correctly it could cause the same problem. I have seen a bottle battery that broke like this and it caused the same problem.

Hall effect sensrs in the motor can also be a possible problem.

-SP

what about inside bike?

No matter how urgent the problem and motor failure can cause some very urgent problems always develop a plan of attack before you start repair work.

I have never seen anyone suggest the method you are proposing. Never.

It would be useful to know something about the type of motor, controller, and battery, it's age, and usage pattern, whether it is brand new, suddenly developed this problem out of the clear blue sky, or if, maybe, just maybe, something unusual or slightly different happened to the kit, which WAS working, and afterwards, is NOT working.

There are a large number of possibilities, without additional information, any guess is a shot in the dark. It is quite possible, even likely, that a careful reading of the questions I have posed and a thorough set of answers will narrow down the field considerably.

The suggestion or implementation of ANY diagnostic test or possible solution without that information is sheer foolishness.

The absolute most common cause of ebike problems, including ones that sound very much like yours, is either a loose or broken connection, or a torn, melted, or otherwise damaged wire. Careful visual inspection can be performed without ANY CHANGES at all to the system, no disassembly, little chance for further damage to occur.

In my opinion, the motor is better

Is this a new install of a kit, or it it an existing bike that had been running properly earlier?

Is battery up and charged?

If hub motor, will wheel spin freely in either direction with and without controller powered up?