Educate yourself in the operation of the mechanical e-unit. The Lionel Service Documents (available in Greenberg Publications, Aurotech Publications, LCCA/HSL) has an excellent section devoted to the theory of operation and that it cycles through F-N-R-N. Ensure that the e-unit lever is in the electrically engaged position so that it will cycle the e-unit drum. Ensure that the e-unit drum and fingers are clean (CRC 2-26 or similar contact cleaner is great for this). Also double check the wiring, that it is intact and follows the traditional field armature series motor.
You cal also wire the motor bypassing the e-unit like so to test the motor functionality.
This should nudge you in the right direction, and please ask clarifying questions as I know I didn't go deep on everything mentioned.