Dodge RAM TRUCK 1500 1995 Service Manual page 1706

25 - 8 EMISSION CONTROL SYSTEMS — — -
Fig. 6 PCV Valve/Hose—3.9U5.2U5.9L Engines-
Typical
A closed engine crankcase breather/filter, with a
hose connecting it to the air cleaner housing, pro­
vides the source of air for system.
The PCV system operates by engine intake mani­
fold vacuum (Fig. 7). Filtered air is routed into the
crankcase through the air cleaner hose and crank­
case breather/filter. This forces crankcase vapors
through the PCV valve. It is then drawn into a pas­
sage in the intake manifold. Here it becomes part of
— — — - B R
Fig. 7 Typical Closed Crankcase Ventilation System
POSITIVE CRANKCASE VENTILATION (PCV)
VALVE
The PCV valve contains a spring loaded plunger.
This plunger meters the amount of crankcase vapors
routed into the combustion chamber based on intake
manifold vacuum.
When the engine is not operating or during an en­
gine popback, the spring forces the plunger back
against the seat. This will prevent vapors from flow­
ing through the valve (Fig. 8).
J9025-20
Fig. 8 Engine Off or Engine PopBack—No Vapor
Flow
During periods of high manifold vacuum, such as
idle or cruising speeds, vacuum is sufficient to com­
pletely compress spring. It will then pull the plunger
to the top of the valve (Fig. 9). In this position there
is minimal vapor flow through the valve.
During periods of moderate manifold vacuum, the
plunger is only pulled part way back from inlet. This
results in maximum vapor flow through the valve
(Fig. 10).
TESTING
(1) With engine idling, remove the PCV valve from
the cylinder head (valve) cover. If the valve is not
The cap has a threaded configuration. This allows
the seal to be broken and pressure to be relieved
without separation of cap from filler tube. Approxi­
mately two and a half turns are required to remove
the cap.
If replacement of filler tube cap is necessary, it
must be replaced with an Identical cap to be sure of
correct system operation.
CAUTION: Remove the fuel tank- filler tube cap to
relieve any fuel tank pressure. The cap must be re­
moved prior to disconnecting any fuel system com­
ponent or before draining the fuel tank.
P 0 S 1 T 1 1 E C i A N I C A S E W E N T i l A T i O l (PCV)
S Y S T E i
DESCRIPTION/OPERATION
All 3.9L V-6 and 5.2L/5.9L V-8 gas powered engines
are equipped with a closed crankcase ventilation sys­
tem and a positive crankcase ventilation (PCV) valve.
The 8.0L V-10 engine is not equipped with a PCV
valve. Refer to Crankcase Ventilation System—8.OL
V-10 Engine for information.
This PCV system consists of a PCV valve mounted
on the cylinder head (valve) cover with a hose ex­
tending from the valve to the intake manifold (Fig.
6).
the calibrated air/fuel mixture to be consumed in the
combustion chamber. The PCV system constantly
ventilates the crankcase to help prevent sludge for­
mation and vapors from entering the atmosphere.