2012 Focus Custom Ram Air How-To

[DaeGoesFast]

Looking at the pictures, I can't tell if the mod introduces the air before or after the MAF sensor. If before, I'd say your fine since the computer should still know exactly how much air is going to the engine. However, if the mod introduces air after the MAF sensor, then your air flow past the sensor should decrease, and may cause the computer to spray less fuel into each cylinder charge, which would explain the significant MPG increase. This may not be a big deal (my car has had the CEL on for years due to a lean fuel code), but I've heard that lean fuel mixtures can be harmful at higher RPMs, due to the hotter combustion of a lean mixture.