Carbon Blasting
A cleaning procedure that uses high-pressure media, such as walnut shells, to remove carbon buildup from intake valves.
Carbon blasting, often referred to as walnut blasting, is a specialized maintenance procedure used to clean heavy carbon deposits from the intake valves and ports of gasoline direct-injection (GDI) engines. Because GDI engines spray fuel directly into the combustion chamber rather than over the intake valves, the valves are not washed clean by gasoline detergents, leading to rapid carbon accumulation.
The process involves using compressed air to blast crushed walnut shell media into the intake runner ports while the intake valves are closed. The walnut shells are hard enough to break up and scour away the baked-on carbon, but soft enough not to damage the steel or aluminum valve guides, stems, and seats. A vacuum adapter sucks out the carbon debris and spent media simultaneously to keep the combustion chamber clean.
Symptoms of carbon buildup needing carbon blasting include engine misfires, rough idling, hesitation during acceleration, and decreased fuel economy. Technicians typically perform this service every 40,000 to 60,000 miles on affected GDI engines. A borescope inspection is used to check the cleanliness of the intake valves before reassembling the intake manifold.