Direct Injected Engines with Excessive Carbon Deposits Explained

I’m sure you have noticed the increase in fuel efficient vehicles being sold in the last few years. The main reason for this is Direct Fuel Injection Systems. It’s basically a gasoline engine operating like a diesel with spark plugs. The problems with these new systems has been an increase in very heavy deposits on the intake valves which are restricting air flow into the engine and turning on check engine lights. This is not isolated to just one manufacturer as it is a flaw in the design, or is it. This problem happened on older style fuel systems but we were able to control it with cleaners run through the fuel system using many different methods. The fuel would in essence wash off the valves as it passed over them. Direct injected engines have the fuel charge placed directly into the combustion chamber and thus make the method of cleaning with fuel ineffective as the raw fuel never touches the intake valves.

 GDI engine

I believe if this were a flaw in the design, every car with 80,000 miles on it would need the valves accessed and sand blasted clean using the walnut cleaning method or manually scrubbed with brushes and cleaners; really the only two methods I have seen to effectively work. Interestingly enough this is not the case as many cars are being driven over double that distance without incident and still some are failing in as little as 40,000 miles.

The deposits that we find on the valves are very oily in nature and I believe they are a result of the crank case fumes passing through the breather system over the valves to be burned up in the combustion process. These oily fumes seem to easily stick to the valves, building up over time, which is causing all the issues. Since there is no real inexpensive way to clean them, the real question is how to prevent it from happening in the first place.

GDI Valves

The type of the engine oil base stock (POA, Hydrocracked, and Petroleum Etc.), the design of the oils additive packages and how often you change your oil are critical in keeping this problem in check. A Simple test of this theory is cooking with oil on a stove. You will notice that when you first start cooking, the oil is clean but as it heats up and it starts to darken you will notice an oily smoke coming off the oil. This vapor will stick to the sides of your pot, your stove and the walls. Your engine does the exact same thing to the oil and even though there are many special additives in the oil designed to slow this process down, it still happens over time. The longer you stretch out the oil change the faster the oil will be susceptible to vaporizing and the worse the buildup will be.

When we change your oil, we will show you a sample of what came out and review with you what interval or oil type seems to work the best for your specific situation. I have found that some oils don’t do very well in certain applications but have also found based on driver habits, the engine design, recent trips etc. that those same oils can do very well. The long and short is if your shop isn’t watching the condition of your oil every time it’s serviced, how will he know what to recommend to improve the situation. If your valves need to be cleaned, you now know your oil service procedures must be modified. Do not solely rely on the reminder system built into the car, the owner’s manual or the oil brand that “paid” to have their name placed under the hood. Be careful with recommendations on running fuel with better cleaners and additives that you can add to the tanks. Even the manufacturers will recommend these steps in TSB’s; I personally have not found one that actually cleans up and solves this issue.

Jim Nelson

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