Walnut Decoking, The best way to fix Carbon build up
Carbon build up is a growing problem for many BMW and MNI engines, here at TWG Automotive we use the Walnut Decoking method (which was developed by BMW themselves) to clean the valves of your BMW or MINI, to get them back to new condition. Below is some information on why and how we carry out this process.
With the demand for manufacturers to make cars more efficient they have made modern petrol engines direct injection compared to the previously used non-direct injection. Direct and non-direct injection refer to how the fuel is actually put into the engine. This change to direct injection can cause carbon deposits to build up on the intake valves which in previous years have not been an issue.
The easiest way to explain how and why this happens is to give a brief understanding of the two different types of fuel injection. Non direct injection engines inject fuel either into the intake manifold or just before the intake valve so it can mix with the air coming into the engine before entering the combustion chamber and making the “bang”. As petrol is a paraffin based product it contains a lot of cleaning properties so as it passes over the intake valves going into the cylinder it cleans off any dirt/carbon deposits that are on the valves which can come from oil vapour re-cycled through the engine breather system.
Cars affected by this type of carbon build up are those with any direct injection engine
With direct injection, petrol is injected at very high pressure, directly into the combustion chamber of the engine completely bypassing the inlet manifold and valves . This means there is no petrol passing over the intake valves to “clean” off the carbon deposits and therefore carbon can form on the intake valves and the intake ports (the intake port is the passage the air goes through to get to the valves).
Cars affected by this type of carbon build up are those with any direct injection engine especially if the car is turbo charged as turbos are known to pass small amounts of oil vapour through the seals, therefore creating a quicker carbon build up. The cars mainly effected are the R56 MINI Cooper S (with the N14 engine), BMW N54 engined cars (which includes the 335i and 135i) and the N47/N57 Diesel engined cars. Driving characteristics have a big effect on the carbon build up too; lots of short start stop journeys can create more vapour in the engine and cause the engine to carbon up quicker.
The effects of this carbon build can be many. Customers have complained of poor mpg, lumpy idle and loss of power. The reason is because the carbon restricts air from getting into the engine and disturbs the way it flows into the engine which both affect how well the combustion in the engine occurs (remember in simple terms the bigger the bang the more power the engine produces)
So what can I do?
The easiest way to limit the effect of carbon build up is to have the valves decoked using a Walnut Blaster. This is a much better method than many fluid based decoke solutions that either connect through the fuel system (due to the direct injection the fluid wouldn’t actually get on to the valves) or work by manually spraying the fluid through the intake. This would struggle to completely clean the valves and ports due to how hard and tough the carbon is when it forms. The other way would be to strip the engine.
The Walnut blaster we use was developed by BMW to enable the decoking of the intake valves without having to strip the engine down and manually clean it, which is a very expensive and time consuming job. It blasts at high pressure, small walnut shell granules on to the carbon; this dries it and allows it to crumble off without causing damage to the cylinder head. Whilst the granules are being blasted there is a special adaptor that connects to a vacuum cleaner that sucks the old walnut shells out together with the carbon particles so nothing is left in the port or on the valves. This process means we can de-carbon the intake valves in a cost effective manner with guaranteed results (we can happily provide pre and post pictures so you can see for yourself how well it works).