Carbon Cleaning & Walnut Blasting
Direct-injection engines build carbon on the intake valves. Walnut blasting removes it and brings back smooth idle and lost power.
Which cars are affected
- BMW N54, N55, N20, N26, N63, B46/B48 and B58 (Gen 1 and Gen 2)
- VW and Audi EA888 2.0T (especially Gen 1 and Gen 2), 1.8T and 3.0T
- MINI Cooper S and JCW (N14, N18)
- Most direct-injection European engines from about 2007 on
Symptoms to watch for
- Rough or shaky idle, especially on a cold start
- Misfires and check engine light
- Gradual loss of power and fuel economy
- Hesitation under acceleration
Why carbon builds up
In a direct-injection engine, fuel is sprayed straight into the cylinder instead of over the intake valves. Port-injected engines get a constant wash of fuel over the valves that keeps them clean; DI engines don't. Oil vapor from the crankcase ventilation bakes onto the valves and builds up a hard carbon layer that disrupts airflow. Short trips and a failing PCV system make it worse. Engines that add port injection, like the newest B58 and later EA888, build up much less.
Why walnut blasting
Fuel additives and spray cleaners don't remove baked-on carbon from intake valves. Walnut blasting uses crushed walnut shell, which is hard enough to remove carbon but soft enough not to damage the valves or seats. We remove the intake manifold, clean each port with the valve closed, vacuum out all media and reassemble with new gaskets.
When to do it
Many DI engines benefit from cleaning somewhere between about 50,000 and 80,000 miles, sooner if the car is driven mostly short distances. We can inspect the valves with a borescope first so you see the buildup before deciding.
Related
BMW Oil Leak Repair · VW PCV Valve & Oil Leak Repair · Engine & Drivetrain Repair
Request a call back
Leave your number and we'll call you back during shop hours. Add your VIN and we can look up your car before we call.
Common questions
Will carbon cleaning fix my misfire?
If carbon is the cause, it usually makes a big difference. We check coils, plugs and injectors first so we're fixing the right thing.
Does my car need it if it runs fine?
Not necessarily. A borescope inspection shows how much buildup there is, and you can plan the job rather than waiting for symptoms.
How long does walnut blasting take?
Typically a day in the shop, depending on how much has to come apart for access.