GDI Engines and Carbon Build-up

GDI (Gasonline Direct Injection) engines have been around for over 100 years. However they have not been used on mass produced automobiles until Mitsubishi released the Galant in 1996. Since then GDI has been gaining more and more popularity due to stricter EPA emission requirements and higher mpg goals. GDI stands for gasoline direct injection. It’s a type of engine where the fuel is injected directly into the combustion chamber. Non GDI engines inject fuel into the intake ports where it mixes with the incoming air.

How Port Fuel Injection Works

First off let’s discuss port fuel injection. Port fuel injection has been used extensively in the automotive industry for years. Port injection, injects fuel into the intake manifold at a low pressure. This fuel then mixed with the air which came from the air intake. The intake valve is then opened creating suction, and the air and fuel mixture is pulled into the combustion chamber and is ignited. This air to fuel mixture is kept at around 14.7 parts are to 1 part oxygen. The gasoline washes over the backside of the valve as it enters the combustion chamber. This is crucial to preventing carbon build-up on the valves. Gasoline contains many additives which can clean the parts they come in contact with. Although port fuel injection is simpler, it is not as efficient as a GDI system.

How Gasoline Direct Injection Works

GDI Systems work by injecting high pressure fuel directly into the combustion chamber. This allows the ECU (engine control unit) to mix the exact amount of fuel needed with the air entering the combustion chamber. In fact the fuel mixture can be adjusted multiple times per second. This allows the ECU to nearly instantly adapt the fuel mixture depending on engine load. The air to fuel mixture can be up to 40 parts air to 1 part fuel. This means that the fuel will have a much more complete burn than port injection. This complete burn increases efficiency and reduces emissions. It also allows a GDI engine to make more power per displacement than a non-GDI engine. These advantages however are not without disadvantages.

Disadvantages of GDI Engines

GDI engines have one major disadvantage than port fuel injection. In a GDI system, fuel is injected directly into the combustion chamber. The gasoline never gets a chance to run over the back side of the intake valve. In other words, the intake valve will never get cleaned by the gasoline. In addition to the valve not being cleaned, it will also not be cooled as efficiently. GDI engines’ valves generally run hotter than direct port injection engines. This added heat and lack of cleaning can lead to a major problem with the intake valves called carbon buildup.

Carbon buildup on the intake valves blocks air flow to the cylinders, and this can cause noticeable reductions in horsepower and fuel economy. The carbon buildup on the cylinder head can cause premature ignition, hard starts, and rough idling. It might also cause misfires and foul spark plugs. The buildup can even break off and cause other problems such as burning a hole through the catalytic converter. Modern engines are using variable valve timing more and more. This keeps the intake valves open for longer periods of time. This increases the chance of carbon buildup due to longer exposure to the combustion chamber.

In summary issues with carbon buildup can be seen below:

  • Check engine light
  • Loss of power
  • Poor acceleration
  • Rough running
  • Stalling
  • Engine misfires
  • Reduced fuel efficiency

How To Prevent Carbon Buildup

There are several actions you can take to help fight carbon buildup. Although carbon buildup can still happen, taking these actions will reduce the probability of issues.

  • Change the oil according the manufacturers recommended interval or before
  • Replace the spark plugs at the recommended interval. If the spark plugs are fouled replace them no matter how many miles are on the plugs. Spark plugs help ensure a complete and through combustion.
  • Use a fuel system cleaner to keep the GDI system healthy.

Some manufacturers like Toyota, have taken a proactive approach to preventing carbon buildup. What they’ve done is they use both low pressure port injection fuel injectors, and fuel injectors which inject directly into the combustion chamber. This allows the engine to get the benefits of direct injection, but the low pressure port injectors are able to clean the intake valves and prevent carbon buildup.

How To Remove Carbon Buildup

Unfortunately if you already have carbon buildup, fuel additives will not get the job done, since the gasoline doesn’t contact the intake valve. However there is a solution. There are several products on the market which can be sprayed in the car’s intake that will coat the valves and attack the carbon buildup on them. CRC GDI Intake Valve Cleaner is one such product. This product has been proven to remove carbon buildup in as little as one hour. If you do end up using one of these products be sure to read the instructions thoroughly and follow the directions dutifully.

Sources

https://www.knowyourparts.com/technical-resources/chemicals/gdi-engines-carbon-buildup/