L-Series Wagon 4WD F4-1781cc 1.8L SOHC (Carb) (1987)
Positive Crankcase Ventilation: Description and Operation
Fig. 1 Positive crankcase ventilation system. Carbureted models
This system, Fig. 1 prevents emission of blow-by gasses from crankcase into atmosphere. At part-throttle operation, blow-by gasses flow from
crankcase through connecting hose on 2-4 rocker cover to PCV valve, which is operated by manifold vacuum, and into intake manifold. Ambient air is
drawn through air cleaner and into crankcase via connecting hose on 1-3 rocker cover. Ambient air then combines with blow-by gasses and enters intake
manifold.
During wide open throttle operation manifold vacuum is not sufficient to allow all of the blow-by gasses to enter intake manifold so excess blow-by
gas enters air cleaner through connecting hose on 1-3 rocker cover where it is drawn into carburetor.
Under some driving conditions, oil from crankcase will blow through connecting hose of 2-4 rocker cover and could be drawn into intake manifold by
force of vacuum. A connecting hose from air cleaner to connecting hose on 2-4 rocker cover prevents this by reducing vacuum.