JinMing M4A1 not shooting

I have recently pulled my gearbox housing apart. I have put everything back together and it looks like it is fine.
However, when I shoot the gun, the motor makes a different sound to before (like it’s all motor and no plunger?), and the gels only enter the barrel slowly and do not shoot out of it.
Has anyone encountered this before, and what did you do to fix it?
Any recommendations on how to get the required pressure to shoot the gels would be appreciated.

it could be one of a couple possibilities, the positive and negative wires to the motor terminals could be mixed up. the plunger isn’t aligned with the sector gears teeth, or plunger isn’t aligned with the guide rails that keep the ladder teeth inline with the sector gear. or cyclinder head isn’t properly sealed within a cyclinder. have you taken apart the gearbox and tested the cyclinder head ,cyclinder and piston for any air leaks