Carbon build-up on intake valves and ports has been a problem for a long time.

After all, we are burning hydrocarbons (fuel) in internal combustion engines; also the insides of these engines are bathed in hydrocarbons (engine oil). Everything is hot. Any unburned or partially burned dose of these fluids can leave a carbon residue. In this article you will learn about the Cause and Effect of Carbon Build Up In GDI Engines and How to Prevent and Clean Carbon from engines.

In the old days, when air and fuel into the cylinders was metered through a carburetor, and later, when fuel was injected into the intake ports, raw fuel, usually with detergent additives, flowed through the intake ports and over the intake valves, washing off most of the unburned residue from those surfaces.

However, in the late 1990s and increasingly during the 2000s, most car manufacturers switched their power plants to gasoline direct injection (GDI). In this system, fuel is injected directly into the combustions chambers, completely bypassing the intake valves. This allows design engineers much greater control over fuel quantity, fuel atomization and combustion efficiency. The resulting decrease in fuel consumption is accompanied by greater efficiency in power production. Modern engines are far stingier with fuel at the same time that they are more powerful than engine designs of a few decades ago.

But there is a cost to this. Without fuel flow through the intake manifold and over the intake valves and seats, there is no cleaning of carbon deposits.

Mercedes-Benz carbon build-up

Where is the carbon coming from?

We are talking about the cause and effect of the carbon build up, so where is it coming from? Remember that, among many other factors, decreasing drag and friction within the engine and between engine components leads to increased efficiency. Starting in the early 1970s with Mobil 1, organic oils were slowly replaced by synthetic lubricants; these oils feature high flow rate and low viscosity at a wide range of temperatures and that has become one of the foundations of modern engine efficiency. Low viscosity oil when cold, low friction piston rings, combined with precise metering of fuel injected directly into combustion chambers, allows an engine that has not reached operating temperature to run much cleaner than was formerly possible.

One of the risks of this strategy is that there is a higher chance of oil dilution due to unburned fuel running down cylinder walls past those low-friction rings. Hydrocarbon vapors in the crankcase, a combination of the thin oil and unburned fuel, are then siphoned by the PCV system into the intake ports. Most of that additional hydrocarbon is burned in the combustion chamber, but some ends up on valve stems and intake ports and begins to cake up in the absence of raw gasoline flushing though these ports.

Valvoline engineers have visually documented another source of unwanted hydrocarbons in the intake ports: Oil is drawn past the valve stem seals and seeps onto the valve stems and heads. This has happened on all makes of cars for a long time, but in GDI engines, since no gasoline and its mix of detergents flow past the intake valves, unburned and partially burned oil cakes up on valve stems, heads and seats as carbon deposits.

The effect of these carbon deposits is quite variable. Initially they disturb airflow into combustion chambers slightly, causing misfires. Combustion chambers in a GDI engine are designed to swirl the intake air and spritzed fuel in a predictable pattern, with high concentrations of fuel “stratified” close to the spark plugs and lower concentrations further away. The high fuel –air ratio close to the spark plug ignites easily and then the flame front spreads to the leaner mixture farther away.

Unfortunately, carbon piling up on intake valves disrupts the air swirl so there are dead spots and mini-explosions in the combustion chambers. The ECM detects these as misfires. Eventually, the ECM can shut the entire system down.

It is far better to deal with carbon build-up proactively, long before misfires or, worse, engine shut-downs occur.

Worldwide pollution standards were forced initially by the need to reduce vehicle emissions for health reasons. Now, increasingly, concerns over the effect of CO2 emissions on global climate systems and the need to increase the efficiency of internal combustion engines, have driven nearly all automotive manufacturers to adopt GDI as a standard. This means that intake valve carbon build-up is routinely found on nearly all makes and models of newer cars. Some, like Volkswagen-Audi and BMW products are susceptible to this problem as early as 30,000 miles. Manufacturers such as Ford and GM continue to deny the prevalence of the problem in their vehicles, but it is by no means rare, in any make or model.

Systemic solutions to the problem currently involve varying the formulation of oil, changing combustion chamber design, and reprogramming valve and ignition timing. Ford is also experimenting with a hybrid direct-indirect injection system: Fuel is injected into the combustion chambers as in GDI but also some is injected into the intake ports in order to clean the valve heads.

A maintenance note: Though modern engines with their very tight tolerances run incredibly clean compared to older models, oil dilution, as mentioned above, is still a problem. Despite manufacturers often writing their owner’s manuals and other literature recommending infrequent oil changes (7,500 or even 15,000 mile intervals) it is now accepted that GDI engines should have an oil change every 5000 miles in order to reduce the chances of intake valve and port carbon buildup. Follow the manufacturer’s recommendations for oil grade and viscosity.

Diagnosing carbon buildup

As mentioned previously, GDI is now practically the only fuel-injection system used in modern vehicles. If a vehicles with GDI engine management arrives in the shop, do not abandon common sense. Check the basics. Make sure there is fuel in the tank and the fuel pump works. Make sure the electrical system is up for cranking and starting the engine.

Check the ECM for fault codes.

Here are some typical codes that might indicate carbon buildup:

  • Random and single cylinder misfires: P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308
  • Cylinder(s) disabled: P1300, P1301, P1302, P1303, P1304, P1305, P1306, P1307, P1308

Another diagnostic path is to attach a pressure transducer to the intake manifold while cranking the engine. If one or more cylinders show lower vacuum during intake strokes, that can indicate partially plugged intakes due to carbon buildup. This condition can also show up on a compression test: Carbon buildup on intake ports obstructs intake air so that the compression in the cylinder is slow to rise, though it eventually reaches normal.

In the past, intake valve and cylinder head cleaning, not simple and straight-forward repairs, were required for carbon-deposit removal. As a work-around, some cylinder head ports could be cleaned with a high-pressure stream of a dry scouring powder that was not abrasive to metal, such as refined walnut shells.

The current state-of-the-art carbon cleaning technology is marketed by ATS Chemical.

The 3C Intelligent Induction Cleaner is our state-of-the-art carbon cleaning technology. The 3C Intelligent Induction Cleaner delivers carefully blended chemicals which cleans carbon build up off the intake valves while the engine is running in under 15 minutes. This can be used to clean and remove excessive build up when engine drivability concerns are present, or for routine maintenance to prevent carbon build up.

Doing this service at regular intervals is akin to flushing brake fluid at 30k miles or 2 years – you prevent much worse problems down the line.

ATS recommends the intake-cleaning procedure at 30,000 mile intervals. The procedure is relatively economical so it can be packaged with the normal 30k mile service at a reasonable cost. The advantage of this is that carbon-buildup on intake surfaces at 30k miles is relatively slight, and the carbon is still rather soft, rather than thickly caked on and cooked into place. It comes off quickly, and is not allowed to build up so that it can affect engine performance noticeably. Doing this service at regular intervals is akin to flushing brake fluid at 30k miles or 2 years – you prevent much worse problems down the line.

ATS Carbon Clean also recommends using our 505 CRF pour in treatment every other oil change or about 10,000 miles. Our advanced pour-in fuel treatment that enhances gasoline to remove carbon deposits from the internal combustion engine and engine components. This chemical mixture is proven to remove carbon from; fuel injectors, induction ports, induction valves, and combustion chambers. Carbon deposits on the injectors can cause drivability problems and poor fuel mileage. This advanced formula can clean coking from the port style injector and the direct style injector; increasing engine performance and fuel economy.

Knowing when and how to clean and prevent carbon build up in gasoline direct inject (GDI) engines is a must when servicing today’s vehicles. Most vehicle owners are not aware of this problem and will not know to ask for a service. The first time you see the vehicle, it will likely have carbon build up and possible drivability degradation. However, educating your customer to the benefits of preventive maintenance will save them money and prevent unwanted vehicle downtime.

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