Direct Injection fuel systems work by “directly injecting” fuel into the cylinder combustion chamber. This enables the vehicle to be much more fuel-efficient all around and helps manufacturers to meet emission control standards. The Direct Injection fuel system is designed for the injectors to inject fuel directly into the cylinders. Other fuel systems such as port injection, inject fuel into the inlet ports, the benefit of this system is that it cleans your valves and inlet ports with the detergents found in most fuel station pumps, examples are Shell V-Power, Vortex Premium.
Direct Injection fuel systems, do not get cleaned by the detergents, this eventually leads to a large amount of carbon build-up over time on newer BMW Turbo, VW TSI and AUDI TFSI engines which requires the Walnut Shell Blasting service.