Pixhawk build motor not spinning with the others after successfull auto tune

I completed a new build with pixhawk. everything went smoothly. during first spin up followed the directions watched some youtube and successfully completed the all in one calibration. Began to spin them up and #4 motor is not playing along. It does not go to the minimum spin speed like the other. Does not spin to about half throttle. If no changes in the throttle it will eventually stop. Is there a way to individually calibrate the ESC to remove that as a possibility. I switched motors and they are all performing fine. It could be the ESC itself but as it is soldered in and beautifully nested i would like to entertain that notion last if possible. Question, comments, concerns ?