I got a bad motor can u help me identify which one

[Fxt4me]

I have a stock F450 with very bad drift to the rear right side of the craft ( about 140 degrees on a compass). I have labeled motors A B C D with A on arm 1, B on arm 2 ect. I switched all 4 motor placement, front 2 changed with back 2 but keeping each motor on the same side IE: Arm 1 is now D, arm 4 is now A, arm 2 is C and arm 3 is B and now the F450 drifts forward and right (about 40 degrees) Obviously this drift is caused by a bad motor and I have a new spare to replace it with. I'm just not sure which one to replace, to me it seems that motor D may be lagging behind the other 3 ( or could B be overpowering), but it may be more complex than that. If you can give any advise on what motor to change please do so.
Thanks

 

[Nocteel]

I'm kinda new to MRs but in my short time have had more than my share of motor failures. In all cases however I could just spin the motor by hand and feel that something was wrong. is there any rotation drift as well? If it was me I would just replace motor "D" with your spare and do a quick hover test. Trial and err might end up being the fastest way to know for sure.

 

[ProPilotWannaBe]

Your drifting may not be due to a motor, though it can be. How is your CG? Do you have the GPS position correct in the Assistant Software? Is the aircraft pretty well balanced?