GDI — Gasoline Direct Injection

Gasoline Direct Injection has become the dominant fuel delivery technology on modern engines. Instead of spraying fuel into the intake port like traditional port injection, GDI sprays fuel directly into the combustion chamber at very high pressure. This gives the PCM extremely precise control over how much fuel is delivered and exactly when it enters the cylinder.

GDI systems operate a two-stage fuel delivery. A conventional electric pump in the tank delivers fuel at low pressure — around 60 PSI — to a mechanical high-pressure pump mounted on the engine. This mechanical pump is driven by a camshaft lobe and boosts pressure to 500 to 3,000 PSI or more. The high-pressure fuel rail feeds the direct injectors which spray fuel directly into the combustion chamber during the compression stroke.

On port injection engines, fuel spraying across the back of the intake valves acted as a cleaning agent — it washed away carbon deposits continuously. On GDI engines, no fuel touches the back of the intake valves because it is injected directly into the cylinder. Over time, oil vapors from the PCV system coat the back of the intake valves and bake into hard carbon deposits. These deposits restrict airflow into the cylinder, cause misfires, rough idle, and reduced power. Carbon buildup is the most common GDI-specific maintenance concern. Walnut shell blasting through the intake ports is the most effective cleaning method.