What causes them on the focus st
The majority of failures are on cylinder 4, which is the hottest due to being the furthest from the water pump. There's also a pretty poor timing transition that is noticed in low-moderate load transition that typically occurs in high gear when on cruise (like going over an overpass on the interstate). Finally, it's believed that the ring-gap is too tight from the factory.
Basically, many failures add up to LSPI. There are plenty of instances of abuse and a few from reaching stock component limits as well. When time-equalized, the FiST is showing significantly fewer failures as I've only seen a handful of them so far.