Pontiac FIREBIRD 1972 Service Manual page 745

6D-2 1972 PONTIAC SERVICE MANUAL
Fig. 6D-2 PCV Valve Location ( 3 0 7 V-8)
SEALED OIL
FILLERCAP
S E A L E D 0 1 1
HEAVY ACCELERATION OR NORMAL IDLE OR
H I G H ROAD SPEED ROAD SPEEDS
Fig. 6D-4 Schematic Flow Chart9.C.V. System
-
Typical
(V-8).
The P.C.V. valve is located in the front of the push rod
cover (V-8 except 307), the front of the left rocker arm
cover (307) and on the rear of the rocker arm cover (6-
cyl.) and is connected to the intake manifold by a rubber
hose (Fig. 6D- 1,6D-2,6D-3). An additional hose from the
air cleaner connects to the rocker arm cover.
At idle or normal road speeds, intake manifold vacuum
causes fresh air to be drawn into the air cleaner, at the
same time fresh air is routed from the air cleaner through
the hose connecting it to the rocker arm cover and on into
the crankcase where it joins with the crankcase vapors
(Fig. 6D-4).
This mixture is drawn through the P.C.V. valve and into
the intake manifold where it mixes with the normal fuel-
/air charge and is later burned.
At high road speeds or heavy acceleration, engine blow-by
is increased and, at the same time, intake manifold
vacuum decreases. When this occurs, there is a reverse
action as shown in Fig. 6D-5, and crankcase vapors are
routed through the connecting hose from the rocker arm
cover into the air cleaner. This mixture joins the normal
air charge and passes through the carburetor and into the
intake manifold for burning later in the cycle.
Fig. 6D-3 PCV Valve Location ( 6 Cyl.)
The components of the closed P.C.V. system include a
P.C.V. valve, a sealed oil filler cap, and connecting hoses.
When the engine is not operating, or a manifold pressure
condition such as a backfire exists, the P.C.V. valve is
closed by spring tension to prevent fuel vapors from enter-
ing the crankcase.
PERIODIC SERVICE
CLOSED P.C.V. SYSTEM
Every two years or 24,000 miles, the Closed Positive 1. Disconnect all hoses and blow them out with com-
Crankcase Ventilation System should be serviced as fol- pressed air. If any hose cannot be freed of obstruc-
lows:
tions, replace with hew hose.