We have a 407 that seems to have a mind of it's own.
It will start fine for weeks and then inexplicably start to mess around. This includes Fadec aborted starts, but the temperature gets no where close to 843. Other times it will latch, but not light off. On about the forth or fifth try it will latch, light off and start normally. We think it might be an HMU problem, but haven't swapped it out yet to see if that solves the problem.
We are also using Fadec version 5.356.( the new version)