VW's engine badges — FSI, TFSI, TSI — confuse almost everyone, and they matter because they tell you how the engine makes fuel-and-air and therefore what faults to expect. Here is the plain version.
FSI = Fuel Stratified Injection = direct injection, usually naturally aspirated in GTI-land (the Mk5's 2.0 FSI on the base car). Fuel sprayed straight into the cylinder
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