This worked for me. Specifically using an EXTERNAL curve!
Looking through Unreal’s source code, line 1485 of ChaosWheeledVehicleMovementComponent.cpp checks to see if there is a valid torque curve and disables mechanical simulation if there is not (thereby constructing a vehicle without an engine). For some reason, external curves allow this check to pass while internal curves will not.
Whoever wrote this code initializes the EngineSetup struct to its default values, then checks whether EngineSetup’s torque curve is valid, then it populates EngineSetup with the valid torque curve. Something doesn’t add up here 