Most RTR ESC's, even the brushless, are set up for a stock/spec motor. It might be that the ESC is not able to handle the demands of a mod motor. I cannot find any specs on that specific esc. If the manual states that it can handle motors of that type, you might consider replacing the sensor wire. If that doesn't get it, try another motor to see if by chance it is the onboard sensor in the motor. Try those tips, then post again.