Quote:
Originally Posted by Colin_Campbell
If no fuel touches the back of the valve, how does the valve get dirty enough to need this "treatment"?
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The PCV system recirculates blow-by gasses back into the intake track. This "contaminated" air has oil particulates that stick to the back of the hot valves. Since no fuel (which has detergents to clean these deposits) passes over the back of the valves the carbon just builds-up. Search walnut blasting or N54 carbon build-up. The N55 has better engine ventilation so carbon build-up isn't near as bad as the N54.