Jeep Cherokee (XJ): Evaporative emission controls
OPERATION The evaporation control system prevents the emission
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 evaporative
canister. The canister temporarily holds the
vapors. The Powertrain Control Module (PCM) allows
intake manifold vacuum to draw vapors into the combustion
chambers during certain operating conditions.
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.
When equipped with certain emissions packages, a
Leak Detection Pump (LDP) will be used as part of
the evaporative system for OBD II requirements.
Also refer to Leak Detection Pump.
NOTE: The evaporative system uses specially manufactured
lines/hoses. If replacement becomes necessary,
only use fuel resistant hose. DESCRIPTION The fuel tank is equipped with a rollover valve.
The valve is located on the top of the fuel tank (Fig.
1).
1 - ROLLOVER VALVE OPERATION The rollover valve will prevent fuel flow through
the fuel tank vent (EVAP) hoses in the event of an
accidental vehicle rollover. The EVAP canister draws
fuel vapors from the fuel tank through this valve. The valve cannot be serviced separately. If replacement
is necessary, the fuel tank must be replaced. 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).
1 - CANISTER MOUNTING BRACKET 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. OPERATION The duty cycle EVAP canister purge solenoid (DCP)
regulates the rate of vapor flow from the EVAP canister
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 solenoid.
When de-energized, no vapors are purged. The
PCM de-energizes the solenoid during open loop operation.
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 conditions.
The PCM varies the vapor flow rate by changing
solenoid pulse width. Pulse width is the amount
of time that the solenoid is energized. The PCM
adjusts solenoid pulse width based on engine operating
condition. 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 40F and 86F, 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 energized
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.
1 - DUTY CYCLE PURGE SOLENOID (DCPS) DRIVER 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). 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 connected
to front of cylinder head cover on 4.0L
engines. It is connected to rear of cover on 2.5L
engines.
1 - AIR INLET FITTING
1 - AIR INLET FITTING 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. DESCRIPTION All vehicles are equipped with a combined VECI
label. This label is located in the engine compartment
(Fig. 6).
1 - VECI LABEL OPERATION The VECI label contains the following: The label also contains an engine vacuum schematic.
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 permanently
attached and cannot be removed without
defacing information and destroying label. A vacuum schematic for emission related items can
be found on the Vehicle Emission Control Information
(VECI) label. For label location, refer to Vehicle
Emission Control Information (VECI) Label. Leak detection pump (LDP) Refer to the appropriate Powertrain Diagnostic
Procedures service manual for LDP testing procedures. 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 necessary,
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 prevent
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. 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 canister.
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.
1 - CANISTER MOUNTING BRACKET REMOVAL The solenoid attaches to a bracket located in rightrear
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 solenoid.
(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. 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.
1 - ELECTRICAL CONNECTOR
1 - LDP FILTER The LDP is located in the right-rear side of engine
compartment (Fig. 9). The LDP filter is located above
the LDP (Fig. 9). The LDP and LDP filter are
replaced (serviced) as one unit. REMOVAL (1) Carefully remove hose at LDP filter.
(2) Remove LDP filter mounting bolt and remove
from vehicle.
(3) Carefully remove vapor/vacuum lines at LDP.
(4) Disconnect electrical connector at LDP.
(5) Remove 2 LDP mounting screws (Fig. 9) and
remove from vehicle. INSTALLATION (1) Install LDP to mounting bracket. Tighten
screws to 1 N·m (11 in. lbs.) torque.
(2) Install LDP filter to mounting bracket. Tighten
bolt to 7 N·m (65 in. lbs.) torque.
(3) Carefully install vapor/vacuum lines to LDP,
and install hose to LDP filter. The vapor/vacuum
lines and hoses must be firmly connected.
Check the vapor/vacuum lines at the LDP, LDP
filter and EVAP canister purge solenoid for
damage or leaks. If a leak is present, a Diagnostic
Trouble Code (DTC) may be set.
(4) Connect electrical connector to LDP. TORQUE CHART Description Torque EVAP Canister Mounting Nuts (canister-tomounting
bracket) . . . . . . . . . 5 N·m (45 in. lbs.)Description and operation
Evaporation control system
Rollover valve
Fig. 1 Rollover Valve Location
2 - RETAINER CLAMP
3 - LOCKNUT
4 - FUEL PUMP MODULE
5 - FUEL FILTER/FUEL PRESSURE REGULATOR
6 - ALIGNMENT ARROW
7 - PIGTAIL HARNESS
8 - FUEL SUPPLY TUBE
9 - EVAP CANISTER VENT LINEEvap canister
Fig. 2 EVAP Canister Location
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)Duty cycle evap canister purge
solenoid
Leak detection pump (LDP)
Fig. 3 Evaporative System Monitor Schematic-Typical
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 LINECrankcase ventilation system
Fig. 4 CCV System-2.5L Engine-Typical
2 - AIR FILTER COVER
3 - FIXED ORIFICE FITTING
Fig. 5 CCV System-4.0L Engine-Typical
2 - FIXED ORIFICE FITTING
3 - AIR FILTER COVERVehicle emission control
information (veci) label
Fig. 6 VECI Label Location-Typical
Diagnosis and testing
Vacuum schematics
Crankcase ventilation system
Removal and installation
Evap canister
Fig. 7 EVAP Canister Location
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)Duty cycle evap canister purge
solenoid
Rollover valve(s)
Fig. 8 EVAP Canister Purge Solenoid (Without LDP)
2 - VACUUM HARNESS
3 - PURGE SOLENOID
4 - MOUNTING BOLT
Fig. 9 EVAP Canister Purge Solenoid (With LDP)
2 - EVAP SOLENOID
3 - EVAP SYSTEM TEST PORT
4 - EVAP SOLENOID ELEC. CONNECTOR
5 - LDP ELEC. CONNECTOR
6 - LDP MOUNTING SCREWS (2)
7 - LDP
8 - LDP MOUNTING BRACKETLeak detection pump (LDP)
Specifications
EVAP Canister Mounting Bracket Nuts (mounting
bracket-to-body) . . . . . . . . . . 43 N·m (32 in. lbs.)
EVAP Canister Purge Solenoid Bracket-to-Body
Mounting Bolt . . . . . . . . . . . . 5 N·m (45 in. lbs.)
LDP Mounting Screws . . . . . . . . 1 N·m (11 in. lbs.)
High and low limits. Load value
Other materials:
Differential side bearings. Axle shaft oil seal. 181 FBI pinion
Differential side bearings
REMOVAL
(1) Remove differential case from axle housing.
(2) Remove the bearings from the differential case
with Puller/Press C-293-PA, C-293-39 Adapter
Blocks, and Plug SP-3289 (Fig. 35).
Fig. 35 Differential Bearing Removal
1 - SPECIAL TOOL C-293-39
2 - BEARI ...