Direct injection engines are a brilliant design and have many positives when compared to a regular port injected style petrol engine. Unfortunately though, the advantageous nature of the design does have one major flaw.

Due to the fuel being injected directly into the cylinder, none of this fuel passes over the back of the intake valves (as it does in a port injected manifold) and this leads to a build up of carbon on the back of the valves. The fuel (in port injection) has a natural cleaning effect over the valve face, helping to remove this carbon build up and preventing excessive coking.

Over time, as this carbon build up progresses, it can begin to affect airflow into the cylinder. It can cause fuel economy and power development issues.

Once the carbon build up has reached excessive levels, it can cause cold start misfires as it disrupts the shape of the incoming air, which is an important characteristic of the FSI type engines fitted in many models within the VAG range.

Here at Renn, we are equipped with the latest design of the VAG Walnut Blasting Kit. This uses a crushed walnut shell media to blast the carbon deposits out of the intake and off of the valves, whilst simultaneously removing all the debris with the vacuum attachment.

In order to gain access to the ports, the intake manifold must be removed, which can be a lengthy process depending on engine type. This can be discussed at the point of booking.

Our recommendation would always be to remove the injectors at the same time in order to clean the nozzle tips in an ultra sonic bath to help remove deposits which may affect injector spray pattern. If this service is also undertaken, we have the correct tooling to properly remove and replace the delicate injector seals which require accurate calibration at the point of installation to avoid poor fitment or damage.

If you think your vehicle may be suffering from the symptoms described above and have a direct injection engine, it is worth considering this as a possible cause and solution.