On some early Toyota EFI vehicles, a fixed orifice PCV system is used to meter blowby from the crankcase into the intake manifold, where they would be consumed during normal engine operation. This system is simple in design and construction, and provides crankcase ventilation based on the size of the fixed orifice valves and the normal operating characteristics of intake manifold vacuum. The two fixed orifice valves are used to balance the strength of vacuum applied to the crankcase as engine operating conditions change. The biggest drawback of this type system is that blowby production does not always match intake manifold vacuum characteristics.
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