I watched EČ yesterday. This episode doesn't make any sense at all. Or is it just me? As soon as the Enterprise from the present does anything different the future Enterprise (from over 100 years in the past) would not exist anymore, right? So it's not possible to steal any parts from the younger ship. And as T'Pol pointed out: They shouldn't remember the other Enterprise at all.
I also think it would have been a good idea to search for the ship they stole the warp coil from in the beginning of season 4. They say they would need 3 years to get home. The Enterprise could have found them 2 months later and give them a new warp coil. They could have at least mention something like this in S4. As it is now this is a very bad move.