Chrysler DODGE D150 1993 Service Manual page 1484

•
Fig. 2 EVAP Canister Purge Solenoid—Typical
FUEL TANK FILLER TUBE CAP
The fuel tank is sealed with a pressure-vacuum re­
lief fuel tank filler tube cap (Fig. 3). The relief valves
in the cap are a safety feature. They operate only to
prevent excessive pressure or vacuum in tank caused
by a malfunction in system or damage to vent lines.
PLASTIC
GASKET
RN348
Fig. 3 Fuel Tank Filler Tube Cap—Typical
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.
C A U T I O N : Remove the fuel tank filler tube c a p to
relieve any fuel tank pressure. The c a p must be re­
moved prior to disconnecting any fuel system com­
ponent or before draining the fuel tank,
• — - EMISSION CONTROL SYSTEMS 25 - 7
Fig. 4 PCV Valve/Hose—Typical
A closed engine crankcase breather/filter, with a
hose connecting it to the air filter housing, provides
t h e source of air for system.
The PCV system operates by engine intake mani­
fold vacuum (Fig. 5). Filtered air is routed into the
crankcase through the air filter hose and crankcase
breather/filter. This forces crankcase vapors through
the PCV valve. It is then drawn into a passage in the
intake manifold. Here it becomes part of the cali­
brated air/fuel mixture to be consumed in the com­
bustion chamber. The PCV system constantly
ventilates the crankcase to help prevent sludge for­
mation and vapors from entering the atmosphere.
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. 6).
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. 7). In this position there
is minimal vapor flow through the valve.
POSITIVE CRANKCASE VENTILATION (PCV)
SYSTEM
DESCRIPTION/OPERA TION
All gas engines are equipped with a closed crank­
case ventilation system and PCV valve (Fig. 4).
This system consists of a crankcase PCV valve
mounted on the cylinder head (valve) cover with a
hose extending from the valve to the intake mani­
fold.