As long as the VIN (vehicle identification number) located on the left, lower corner of the wind sield (steering wheel side) and/or sticker on left front door maches the one on the vehicle's paperwork AKA "tarjeta de circulacion" or bill of sale you should be OK crossing the border, US customs might take a closer look at the vehicle if the plates are not on it and register the VIN number, be prepared for a thorough vehicle search.
As far as I know if you have a Mexican resident card you do not need the FMM, that is for turistas.
navegator