Direct Injection and Deposits
Sometimes technology moves a little too fast for its own good. If you have bought a vehicle in the last few years and you bought a turbocharged one (smaller turbocharged engine with big engine power and small engine economy) you probably unknowingly bought a gasoline direct injected engine.
Yes, the power was impressive. The fuel mileage …. maybe not so impressive. One thing you may or may not know is that direct injection engines have a propensity to form intake valve deposits.
A bit of background is required here. A gasoline engine requires fuel mixed with air to explode and produce power. The way we mix this air and fuel has changed fairly recently. Think way back and you might remember the carburetor. Air was sucked through a metering device called a carburetor. The venturi effect was used to suck fuel out of a bowl turning it into fine droplets and mixing it with air at a reasonably controlled ratio. This air fuel mix followed a circuitous route into each cylinder of your engine past a gatekeeper called an intake valve.
Along came port fuel injection. Now only the air followed the circuitous route into each cylinder but as it was reaching the intake valve fuel under pressure was sprayed in precise amounts directly at the back of the intake valve. The ratio of air to fuel entering the cylinder was now more precisely controlled than ever. Much better fuel economy, horsepower, and long lasting engines.
In both these technologies the gatekeeper to the explosion chamber (intake valve) was always being washed with a little gasoline mixed with air. Provided the gasoline had the correct detergents intake valve deposits were kept to a minimum. Along comes direct fuel injection. The intake valve is now only letting air into the explosion chamber (cylinder). The fuel is now injected under very high pressure directly into the air that is already in the cylinder. The mixing is just that much better. More power is produced and less fuel is required.
Unfortunately the gatekeeper (intake valve) is no longer getting a little bath as it opens. As you can imagine an explosion chamber is a dirty place at best. Without that fuel washing effect on the intake valve it now builds up deposits of combustion byproducts that start to restrict the air flowing into the engine. Gradually your power and fuel mileage become reduced. Eventually you may experience drivability problems and possibly the associated check engine light.
Poor high speed performance and rough cold idle are the most common symptoms of these intake valve deposits. From what I have read and seen there are no manufacturers using this technology that are immune to these deposits unless they are using two sets of fuel injectors (one set behind the intake valves).
It seems that to this point there is no simple solution to preventing these deposits. Disassembly and physical cleaning is generally required. Depending on the vehicle involved these procedures can be costly.