Jeep XJ. Manual — part 527
The valve cannot be serviced separately. If replace-
ment is necessary, the fuel tank must be replaced.
EVAP CANISTER
DESCRIPTION
A maintenance free, EVAP canister is used on all
vehicles. The EVAP canister is located under the left
side of vehicle near the front of the rear axle (Fig. 2).
OPERATION
The EVAP canister is filled with granules of an
activated carbon mixture. Fuel vapors entering the
EVAP canister are absorbed by the charcoal granules.
Fuel tank pressure vents into the EVAP canister.
Fuel vapors are temporarily held in the canister until
they can be drawn into the intake manifold. The duty
cycle EVAP canister purge solenoid allows the EVAP
canister to be purged at predetermined times and at
certain engine operating conditions.
DUTY CYCLE EVAP CANISTER PURGE
SOLENOID
OPERATION
The duty cycle EVAP canister purge solenoid (DCP)
regulates the rate of vapor flow from the EVAP can-
ister to the intake manifold. The Powertrain Control
Module (PCM) operates the solenoid.
During the cold start warm-up period and the hot
start time delay, the PCM does not energize the sole-
noid. When de-energized, no vapors are purged. The
PCM de-energizes the solenoid during open loop oper-
ation.
The engine enters closed loop operation after it
reaches a specified temperature and the time delay
ends. During closed loop operation, the PCM cycles
(energizes and de-energizes) the solenoid 5 or 10
times per second, depending upon operating condi-
tions. The PCM varies the vapor flow rate by chang-
ing solenoid pulse width. Pulse width is the amount
of time that the solenoid is energized. The PCM
adjusts solenoid pulse width based on engine operat-
ing condition.
LEAK DETECTION PUMP (LDP)
OPERATION
The Leak Detection Pump (LDP) is used only with
certain emission packages.
The LDP is a device used to detect a leak in the
evaporative system.
The pump contains a 3 port solenoid, a pump that
contains a switch, a spring loaded canister vent valve
seal, 2 check valves and a spring/diaphragm.
Immediately after a cold start, engine temperature
between 40°F and 86°F, the 3 port solenoid is briefly
energized. This initializes the pump by drawing air
into the pump cavity and also closes the vent seal.
During non-test test conditions, the vent seal is held
open by the pump diaphragm assembly which pushes
it open at the full travel position. The vent seal will
remain closed while the pump is cycling. This is due
to the operation of the 3 port solenoid which prevents
the diaphragm assembly from reaching full travel.
After the brief initialization period, the solenoid is
de-energized, allowing atmospheric pressure to enter
the pump cavity. This permits the spring to drive the
diaphragm which forces air out of the pump cavity
and into the vent system. When the solenoid is ener-
gized and de-energized, the cycle is repeated creating
flow in typical diaphragm pump fashion. The pump
is controlled in 2 modes:
PUMP MODE: The pump is cycled at a fixed rate
to achieve a rapid pressure build in order to shorten
the overall test time.
TEST MODE: The solenoid is energized with a
fixed duration pulse. Subsequent fixed pulses occur
when the diaphragm reaches the switch closure
point.
The spring in the pump is set so that the system
will achieve an equalized pressure of about 7.5 inches
of water.
When the pump starts, the cycle rate is quite high.
As the system becomes pressurized pump rate drops.
Fig. 2 EVAP Canister Location
1 – CANISTER MOUNTING BRACKET
2 – BRACKET NUTS (3)
3 – EVAP CANISTER
4 – CANISTER MOUNTING NUTS (2)
5 – L. R. SHOCK ABSORBER
6 – EVAP LINES/HOSES
7 – DOWEL PINS AND BUSHINGS (2)
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EMISSION CONTROL SYSTEMS
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DESCRIPTION AND OPERATION (Continued)
If there is no leak the pump will quit. If there is a
leak, the test is terminated at the end of the test
mode.
If there is no leak, the purge monitor is run. If the
cycle rate increases due to the flow through the
purge system, the test is passed and the diagnostic is
complete.
The canister vent valve will unseal the system
after completion of the test sequence as the pump
diaphragm assembly moves to the full travel position.
A typical system schematic is shown in (Fig. 3).
CRANKCASE VENTILATION SYSTEM
DESCRIPTION
All 2.5L 4–cylinder and 4.0L 6–cylinder engines
are equipped with a Closed Crankcase Ventilation
(CCV) system (Fig. 4) or (Fig. 5).
OPERATION
The CCV system performs the same function as a
conventional PCV system, but does not use a vacuum
controlled valve.
On 4.0L 6 cylinder engines, a molded vacuum tube
connects manifold vacuum to top of cylinder head
(valve) cover at dash panel end. The vacuum fitting
contains a fixed orifice of a calibrated size. It meters
the amount of crankcase vapors drawn out of the
engine.
On 2.5L 4 cylinder engines, a fitting on drivers
side of cylinder head (valve) cover contains the
metered orifice. It is connected to manifold vacuum.
A fresh air supply hose from the air cleaner is con-
nected to front of cylinder head cover on 4.0L
engines. It is connected to rear of cover on 2.5L
engines.
Fig. 3 Evaporative System Monitor Schematic—Typical
1 – DUTY CYCLE PURGE SOLENOID (DCPS) DRIVER
2 – POWERTRAIN CONTROL MODULE (PCM)
3 – 3-PORT SOLENOID DRIVER
4 – REMOTE FILTER
5 – COMBINED CANISTER VENT VALVE & LEAK DETECTION
PUMP
6 – CANISTER
7 – TANK ROLLOVER VALVE & VAPOR FLOW CONTROL
ORIFICE
8 – INTAKE MANIFOLD
9 – THROTTLE BODY
10 – DCPS
11 – SWITCH SIGNAL INPUT TO THE PCM
12 – ENGINE VACUUM LINE
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EMISSION CONTROL SYSTEMS
25 - 25
DESCRIPTION AND OPERATION (Continued)
When the engine is operating, fresh air enters the
engine and mixes with crankcase vapors. Manifold
vacuum draws the vapor/air mixture through the
fixed orifice and into the intake manifold. The vapors
are then consumed during combustion.
VEHICLE EMISSION CONTROL INFORMATION
(VECI) LABEL
DESCRIPTION
All vehicles are equipped with a combined VECI
label. This label is located in the engine compart-
ment (Fig. 6).
OPERATION
The VECI label contains the following:
• Engine family and displacement
• Evaporative family
• Emission control system schematic
• Certification application
• Engine timing specifications (if adjustable)
• Idle speeds (if adjustable)
• Spark plug and gap
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.
DIAGNOSIS AND TESTING
VACUUM SCHEMATICS
A vacuum schematic for emission related items can
be found on the Vehicle Emission Control Informa-
tion (VECI) label. For label location, refer to Vehicle
Emission Control Information (VECI) Label.
Fig. 4 CCV System—2.5L Engine—Typical
1 – AIR INLET FITTING
2 – AIR FILTER COVER
3 – FIXED ORIFICE FITTING
Fig. 5 CCV System—4.0L Engine—Typical
1 – AIR INLET FITTING
2 – FIXED ORIFICE FITTING
3 – AIR FILTER COVER
Fig. 6 VECI Label Location—Typical
1 – VECI LABEL
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EMISSION CONTROL SYSTEMS
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DESCRIPTION AND OPERATION (Continued)
LEAK DETECTION PUMP (LDP)
Refer to the appropriate Powertrain Diagnostic
Procedures service manual for LDP testing proce-
dures.
CRANKCASE VENTILATION SYSTEM
TESTING/CLEANING
The Crankcase Ventilation (CCV) system performs
the same function as a conventional PCV system, but
does not use a vacuum controlled valve. A vacuum
fitting containing a fixed orifice of a calibrated size is
used. It meters the amount of crankcase vapors
drawn out of the engine.
(1) Check each CCV system tube (line) for leaks,
cracks, kinks or bends. Replace as necessary
(2) Disconnect each CCV tube..
(3) Blow compressed air through each tube and
check for blockage or restrictions. If cleaning is nec-
essary, spray a soapy-type all-purpose cleaner into
each component and blow out. After restriction is
cleared, rinse out component with clear water. Blow
water from component and install to vehicle. To pre-
vent
damage
to
plastic
components,
never
spray carburetor-type cleaner into any of the
plastic tubes or the fixed orifice fitting. Never
attempt to clean the fixed orifice fitting with a
metal object as calibration could be affected. If
fixed fitting cannot be cleared, replace it.
REMOVAL AND INSTALLATION
EVAP CANISTER
The EVAP canister is located under left side of
vehicle near front of rear axle (Fig. 7).
REMOVAL
(1) Disconnect vacuum hoses/lines at EVAP canis-
ter. Note location of lines before removal.
(2) Remove EVAP canister and mounting bracket
assembly from body (3 nuts).
(3) Remove canister from mounting bracket (2
nuts).
INSTALLATION
(1) Position
canister
into
canister
mounting
bracket. Align 2 canister dowel pins into rubber
bushings.
(2) Install 2 canister nuts and tighten to 5 N·m (45
in. lbs.) torque.
(3) Position canister and bracket assembly to body.
(4) Install 3 nuts and tighten to 43 N·m (32 ft.
lbs.) torque.
(5) Connect vacuum hoses/lines at EVAP canister.
DUTY CYCLE EVAP CANISTER PURGE
SOLENOID
REMOVAL
The solenoid attaches to a bracket located in right-
rear side of engine compartment (Fig. 8) or (Fig. 9).
The top of the solenoid has the word UP or TOP on
it. The solenoid will not operate properly unless it is
installed correctly.
(1) Disconnect electrical wiring connector at sole-
noid.
(2) Disconnect vacuum harness at solenoid.
(3) Remove solenoid and its support bracket.
INSTALLATION
(1) Install EVAP canister purge solenoid and its
mounting bracket to cowl panel.
(2) Tighten bolt to 5 N·m (45 in. lbs.) torque.
(3) Connect vacuum harness and wiring connector.
ROLLOVER VALVE(S)
The rollover valves(s) are/is molded into the fuel
tank and are not serviced separately. If replacement
is necessary, the fuel tank must be replaced. Refer to
Fuel Tank Removal/Installation.
Fig. 7 EVAP Canister Location
1 – CANISTER MOUNTING BRACKET
2 – BRACKET NUTS (3)
3 – EVAP CANISTER
4 – CANISTER MOUNTING NUTS (2)
5 – L. R. SHOCK ABSORBER
6 – EVAP LINES/HOSES
7 – DOWEL PINS AND BUSHINGS (2)
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EMISSION CONTROL SYSTEMS
25 - 27
DIAGNOSIS AND TESTING (Continued)
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