The 2012 and newer Ford Focus (USA version) with the 2.0L naturally aspirated direct injected engine doesn’t seem to have issues with carbon buildup on the valves. Why do other DI engines, especially with turbos have so many issues with carbon buildup that they need to have the valves walnut blasted every so often?
I’ll put that down to some German engineering know-how, just guessing though.
It was an issue with some very early direct injected engines like the SCi engine in the Mk3 Mondeo or the 2.0 FSI engine in the Mk5 Golf. In 2012, the direct injection technology wasn’t a new thing anymore and most manufacturers already had a lot of experience with it.
On turbo engines, you still get that issue sometimes, but that is mostly due to different fuel qualities being available in different markets. Most small turbo engines for sale in North America were initially designed for the European market, where they run very lean to meet stringent emissions regulations. In the North American market, the available fuel quality is lower (mostly due to the higher sulfur content, especially in Diesel fuel), so the engines have to run somewhat richer to meet the same power output as they do in the European models, which can cause carbon buildup on the valves.