Jeep 1996 Grand Cherokee Service Manual - page 1450
EVAPORATIVE EMISSION CONTROLS
INDEX
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DESCRIPTION AND OPERATION
CRANKCASE BREATHER/FILTER—5.2L
ENGINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
CRANKCASE VENTILATION (CCV) SYSTEM—
4.0L ENGINE . . . . . . . . . . . . . . . . . . . . . . . . . . 16
DUTY CYCLE EVAP CANISTER PURGE
SOLENOID . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
EVAPORATION (EVAP) CANISTER . . . . . . . . . . . 13
EVAPORATION CONTROL SYSTEM . . . . . . . . . 13
FUEL TANK FILLER TUBE CAP . . . . . . . . . . . . . 14
LEAK DETECTION PUMP (LDP)—4.0L
CALIFORNIA EMISSIONS PACKAGE . . . . . . . . 15
POSITIVE CRANKCASE VENTILATION (PCV)
SYSTEM—5.2L ENGINE . . . . . . . . . . . . . . . . . 15
PRESSURE RELIEF/ROLLOVER VALVE . . . . . . . 13
VEHICLE EMISSION CONTROL INFORMATION
(VECI) LABEL . . . . . . . . . . . . . . . . . . . . . . . . . 17
DIAGNOSIS AND TESTING
LEAK DETECTION PUMP (LDP) . . . . . . . . . . . . . 19
PCV VALVE TEST—5.2L ENGINE . . . . . . . . . . . . 18
VACUUM SCHEMATICS . . . . . . . . . . . . . . . . . . . 19
REMOVAL AND INSTALLATION
EVAP CANISTER . . . . . . . . . . . . . . . . . . . . . . . . 19
EVAPORATIVE CANISTER PURGE SOLENOID . 19
FUEL TANK FILLER TUBE CAP . . . . . . . . . . . . . 20
LEAK DETECTION PUMP (LDP) . . . . . . . . . . . . . 20
PRESSURE RELIEF/ROLLOVER VALVE . . . . . . . 20
SPECIFICATIONS
TORQUE CHART . . . . . . . . . . . . . . . . . . . . . . . . 21
DESCRIPTION AND OPERATION
EVAPORATION CONTROL SYSTEM
The evaporation control system prevents the emis-
sion of fuel tank vapors into the atmosphere. When
fuel evaporates in the fuel tank, the vapors pass
through vent hoses or tubes to a charcoal filled evap-
orative canister. The canister temporarily holds the
vapors. The Powertrain Control Module (PCM) allows
intake manifold vacuum to draw vapors into the com-
bustion chambers during certain operating condi-
tions.
All engines use a duty cycle purge system. The
PCM controls vapor flow by operating the duty cycle
EVAP purge solenoid. Refer to Duty Cycle EVAP
Purge Solenoid in this section.
The 4.0L six-cylinder engine, when equipped with
the California Emissions Package, will also use a
Leak Detection Pump (LDP) as part of the evapora-
tive system. This pump is used as part of OBD II
requirements. Refer to Leak Detection Pump—4.0L
Engine for additional information.
NOTE: The evaporative system uses specially man-
ufactured hoses. If replacement becomes neces-
sary, only use fuel resistant hose.
PRESSURE RELIEF/ROLLOVER VALVE
A combination fuel tank pressure relief and roll-
over valve is used (Fig. 1). The valve is located on the
top of fuel tank (Fig. 2). This dual function valve will
relieve fuel tank pressure and also prevent fuel flow
through the fuel tank vent hoses in the event of an
accidental vehicle rollover.
The valve incorporates a pressure relief mechanism
that releases fuel tank pressure when the pressure
increases above the calibrated sealing value.
EVAPORATION (EVAP) CANISTER
A maintenance free, EVAP canister is used on all
vehicles. The EVAP canister is located in the engine
compartment below the left front headlamp (Fig. 3)
Fig. 1 Pressure Relief/Rollover Valve
ZJ
EMISSION CONTROL SYSTEMS
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