Direct Injection and Carbon Build-Up – Why It Happens and What You Should Do To Prevent It

Service Engine Soon

You are driving your Audi, when unexpectedly, “Ding!”, your check engine light illuminates on the dashboard. Traveling down the road, suddenly, your BMW runs rough or feels like it will shut off. Why does this happen?


The check engine light covers many systems and components in your European vehicle. One reason for this combination of issues happening is due to the direct injection engine. These engines are the most efficient at low mileage. As the miles are put on the vehicle, fuel directly injected into the cylinder causes a carbon build-up. The direct injection does not allow for the fuel and its detergent additives to clean the valve and the port. The carbon build-up is the reason for the misfire (rough running engine). This signals the check or service engine light to come on, letting the driver know there is an issue with their engine’s performance. This is a typical problem which plagues these engines when the mileage hits 30-60,000.

What Preventive Things Can Car Owners Do?

There are several mechanical ways to solve the carbon build-up. The best prevention is scheduled maintenance. First, full synthetic oil changes should be completed every 5,000 miles. Changing the oil regularly allows for optimal performance of the intake valves.

Secondly, spark plug replacement (at factory recommended mileage) can reduce the amount of unburned fuel in the chambers which can cause the valves to stick.

Thirdly, fuel injector cleaning may help the injector’s spray continue to spray correctly. This service should be done every 30,000 miles (every 2 years) on BMW or every 15-16,000 miles (once per year) on Audi / Volkswagen (this may vary with engine size). Compared to the repair of cleaning the valves with build-up, it is a minor price to pay every other year. This is maintenance which does prevent the carbon build-up.

Independent repair shops typically do this service for 20-30% less than a dealership.

We recommend you shop around for pricing of this preventive maintenance but always consult a shop specialized in repair of European / German vehicles.  If you are in the Las Vegas area, contact Desert Oasis European Auto Service and Repair at 702-255-4090.

The last and non-mechanical prevention item is a new software update on the vehicle’s ECM. This update can reduce carbon deposits by adjusting the timing of the valve and spark.

What happens if the Carbon Build-up Has Occurred?

Everything is not lost if the carbon build-up has already occurred. There is a service in which the carbon deposits can be removed. The process to remove the carbon build-up disassembles the intake manifold and cleans the valves with specialized chemicals, wire brushes, and picks. This process may include soaking, valve scrubbing, and re-soaking. This procedure may repeat many times to remove the carbon. Another tool, the media blaster, may be used as well to clean out carbon build-up. It is much like sandblasting. However, when not applied by a skilled technician it may cause more damage than help.

Not only in this situation, but always consult an automotive technician specializing in European and British vehicles to diagnose and repair your vehicle. Modern vehicles of today, especially those of the European manufacturers, have engineering unique to their designs. Many components are computerized and require diagnostic, programming, and code laptops with pass-through tools exclusive to those manufacturers.

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