DI ie. Direct Ignition engines are used in many major automotive vehicles. But people don't know that their vehicle with time is depleting in performance not because it older but because their is a design fault in DI engine system.

Auto Observer reports that the issue is the tendency of direct injected or DI engines to build up a layer of carbon or soot around the intake valves that can over time significantly affect the performance and economy of the engines. The soot is able to build up in a DI engine because unlike a port injected engine there is no constant spray of fuel that can keep the deposits washed away.

Some engines are more trouble plagued thanks to the direct injection than others. The technology is used in multiple vehicles from different automotive firms including Audi, VW, BMW, Ford and others.

Volkswagen filed a patent application in 2002 that described the issue with DI engines, "Gasoline engines with direct injection of the fuel into the combustion chamber…suffer especially from the problem of the formation of carbon deposits…especially in the neck region of the intake valves." The application also noted that these carbon build-ups "have extremely negative effects" on the performance of the engine.

The patent app was intended to propose a new catalytic surface to the engine that would prevent the buildup of carbon. One automotive enthusiast found out the hard way how much carbon build-up can affect performance. Constantine Boyadjiev purchased a slightly used 2008 Audi RS 4 and later found that carbon build-up is a big issue with the vehicles.

Boyadijev said, "The loss of performance became very noticeable over time." Boyadijev took his RS 4 to a dyno to help document the problem. He reports that when the RS 4 has 15,000 miles on the clock it produced 324 all-wheel horsepower. At 20,000 miles, the same dyno showed 317 AWHP, and at another 5,000 miles, the car produced 305 AWHP.