Jeep Wrangler 1999 Electronic Service Manual page 1208

25 - 8 EMISSION CONTROL SYSTEMS
EVAPORATIVE EMISSION CONTROLS
DESCRIPTION AND OPERATION
EVAPORATION CONTROL SYSTEM . . . . . . . . . . 8
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
Canister Purge Solenoid in this section.
When equipped with certain emissions packages, a
Leak Detection Pump (LDP) will be used as part of
the evaporative system. This pump is used as part of
OBD II requirements. Refer to Leak Detection Pump
in this group for additional information.
NOTE: The evaporative system uses specially man-
ufactured hoses. If replacement becomes neces-
sary, only use fuel resistant hose.
VEHICLE EMISSION CONTROL INFORMATION
(VECI) LABEL
All vehicles are equipped with a combined VECI
label. This label is located in the engine compart-
ment (Fig. 1) and contains the following:
• Engine family and displacement
• Evaporative family
• Emission control system schematic
INDEX
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VEHICLE EMISSION CONTROL INFORMATION
(VECI) LABEL . . . . . . . . . . . . . . . . . . . . . . . . . . 8
• Certification application
• Engine timing specifications (if adjustable)
• Idle speeds (if adjustable)
• Spark plug and gap
VECI LABEL
Fig. 1 VECI Label Location
The label also contains an engine vacuum sche-
matic. There are unique labels for vehicles built for
sale in the state of California and the country of
Canada. Canadian labels are written in both the
English and French languages. These labels are per-
manently attached and cannot be removed without
defacing information and destroying label.
TJ
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