Chrysler DODGE D150 1993 Service Manual page 1483

25 - 6 EMISSION CONTROL SYSTEMS
•
EWAPORATIWE EMISSION CONTROLS
INDEX
page
Crankcase Breather/Filter—Gas Powered
Engines . . .
9
E V A P (Evaporation) Control System .
6
E V A P Canister . . 6
page
Evap Canister Purge Solenoid
6
Fuel Tank Filler Tube C a p . 7
Positive Crankcase Ventilation ( P C V ) System . . . . 7
Pressure Relief/Rollover Valve
6
EVAP (EVAPORATION) CONTROL SYSTEM
GENERAL INFORMATION
The function of the EVAP control system is to pre­
vent t h e emissions of gasoline vapors from t h e fuel
t a n k into t h e atmosphere. When fuel evaporates in
the fuel tank, the vapors pass through vent hoses or
tubes to a carbon filled EVAP canister. They are
temporarily held in the canister until they can be
drawn into t h e intake manifold when t h e engine is
running.
The vapors are drawn into the engine at idle as
well as off idle. This system is called a Bi-level Purge
System where there is a dual source of vacuum to re­
move fuel vapor from the EVAP canister.
The EVAP canister is a feature on all models for
the storage of fuel vapors from t h e fuel tank.
The h o s e s u s e d in this system are specially
manufactured. If replacement b e c o m e s neces­
sary, it is important to u s e only fuel resistant
hose.
PRESSURE RELIEF/ROLLOVER VALVE
These vehicles are equipped with a combination
pressure relief and rollover valve. This dual function
valve will relieve fuel t a n k pressure and also prevent
fuel flow through the fuel t a n k vent hoses in t h e
event of an accidental vehicle rollover.
The valve incorporates a pressure relief mechanism
t h a t releases fuel t a n k pressure when the pressure
increases above t h e calibrated sealing value. Refer to
the Fuel Tank section of Group 14, Fuel Systems for
removal and installation procedures.
EVAP CANISTER
A sealed, maintenance free, EVAP canister is used
on all vehicles. The canister is mounted in t h e en­
gine compartment on the right side wheel well (Fig.
1). The EVAP canister is filled with granules of an
activated carbon mixture. Fuel vapors entering t h e
EVAP canister are absorbed by t h e charcoal gran­
ules.
Fuel t a n k pressure vents into t h e EVAP canister.
Fuel vapors are temporarily held in the canister un­
til they can be drawn into t h e intake manifold. The
EVAP canister purge solenoid allows t h e EVAP can­
ister to be purged at predetermined times and at cer­
tain engine operating conditions.
Refer to t h e Component Removal/Installation sec­
tion of this group for replacement procedures.
EVAPORATIVE
Fig. 1 EVAP Canister Location
EVAP CANISTER PURGE SOLENOID
Vacuum for t h e EVAP canister is controlled by t h e
EVAP canister purge solenoid (Fig. 2). The solenoid
is operated by the powertrain control module (PCM).
The PCM regulates t h e solenoid by switching the
ground circuit on and off based on engine operating
conditions. When energized, the solenoid prevents
vacuum from reaching the EVAP canister. When not
energized, t h e solenoid allows vacuum to flow
through to the EVAP canister.
During warm-up and for a specified time period af­
ter hot starts, the PCM grounds the EVAP canister
purge solenoid causing it to energize. This will pre­
vent vacuum from reaching the EVAP canister
valve. When the engine reaches an operating temper­
ature of approximately 27°C (80°F) and a time delay
interval of about 100 seconds h a s occurred, t h e PCM
removes t h e ground to solenoid. The de-energized so­
lenoid allows vacuum to flow to the EVAP canister
and purge fuel vapors through t h e intake manifold.
The EVAP canister purge solenoid will also be en­
ergized during certain idle conditions in order to up­
date t h e fuel delivery calibration.
Refer to t h e Component Removal/Installation sec­
tion of this group for replacement procedures.