Carbon Build Up: What Is It & How Do I Clean It?

Do you need a “Carbon Clean” Performed on Your Car?

Find out what “carbon build up” is, how to clean carbon build up, and if your car needs to have a carbon clean procedure performed on it – all right here (with pictures)!

“What is Carbon Build Up?”

“Carbon build-up” is a term for a very common issue with direct-injected engines like the ones found in modern Audi models (like the 2.0T, V6’s, and the V8’s like those found in the RS4) and many of the BMW straight-sixes that can be found across the model range. We’ll explain what it is in more detail below, and why you might need a carbon clean performed, but depending on the severity of the problem when it develops it results in several negative effects on the engine and the car’s drivability. These effects and their symptoms can range anywhere from cold-starting problemsignition misfirescheck engine lights (or CEL’s), and drastically reduced engine performance, just to name a few.

Back to what carbon build up is, specifically…

Carbon buildup refers to the accumulation of carbon deposits on the engine cylinders’ intake valves. A car’s engine relies crucially on the exact timing and proper opening/closing of its valve-train in order to run. In other types of engines, both gasoline and air are passed through the intake port into the cylinder and that flow of fuel helps to keep the back of the intake valves clean. Because direct injection circumvents the intake port entirely, gasoline never passes through the intake port and carbon (a by-product from the combustion in the cylinder) can sneak past the valve seats and accumulate on the back side of the valve. The carbon deposits build up over time, gradually impeding the correct operation of the valve-train and both the performance and efficiency of the engine will suffer, resulting in the symptoms mentioned above. According to the Wikipedia entry on direct injection:

Although direct injection provides more power and efficiency, a carbon build-up occurs in the intake valves that over time reduces the airflow to the cylinders, and therefore reduces power. Fuel contains various detergents and can keep the intakes clean. When fuel is no longer being sprayed in the intake valves, small amounts of dirt from intake air and blowback carbon from the crankcase ventilation system cakes on the intake walls, even with air filters that prevent most of the dirt from entering the cylinder. This build-up can become severe enough that a piece can break off and has been known to burn holes in catalytic converters. It can also cause sporadic ignition failures. 

— Wikipedia (Gasoline direct injection)

Such was the case with our customer’s 2008 BMW 3-Series pictured here. He brought his car in to see us when it started running poorly and turning on the Check Engine Light. We quickly determined that the engine had developed a severe “misfire” and began the process of narrowing down the cause. After ruling out spark plugs, ignition coils, etc. we had to dig a little deeper and remove the intake to check the valves. As you can see in the pictures we took, the build-up of carbon on the valves was dramatic. Using a carbon clean method called “walnut shell blasting”, we were able to clean the valves effectively and restore the smooth operation of the engine. Walnut shell blasting is not only highly effective (as you can see in the “after” pictures), it is also completely safe and harmless on engine components.

“How to prevent carbon build up?”

If you’re wondering if you can expect to have a similar issue with your Audi or BMW, it is difficult to say with certainty or predict the mileage at which it may become a problem. According to, the frequency with which the problem occurs could be as high as one in six. That article was from 2015 so the actual figure could be even higher since the mileage at which it happens can vary tremendously. In the case of this BMW, it took about 90,000 miles. We’ve seen it happen as early as 40,000 miles in an Audi before. Unfortunately, there isn’t much that can be done to prevent carbon build up but one way you can potentially slow down the process is with routine, high-quality oil changes performed at least every 5,000 miles. Eventually though, there is a good chance you will need to have that carbon cleaned.

When it comes to the care of your BMW or Audi, or if you are experiencing any of the symptoms described above, give us a call today or schedule an appointment online to have one of our BMW and Audi certified auto repair technicians to help at either our Love Field, White Rock, or Plano locations.

And if you found this information useful then be sure to like and follow Autoscope European Car Repair on Google Plus, Facebook, and Instagram for more!

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