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EMISSION CONTROLS
INDEX
page page
Crankcase Ventilation System................. 5
EVAP (Evaporation) Control System............ 4
EVAP Canister............................ 4Fuel Tank Filler Tube Cap.................... 4
Oxygen (O2S) Sensor....................... 6
Pressure Relief/Rollover Valve................. 6
EVAP (EVAPORATION) CONTROL SYSTEM
GENERAL INFORMATION
The function of the EVAP control system is to pre-
vent the emissions of gasoline vapors from the fuel
tank into the atmosphere. When fuel evaporates in
the fuel tank, the vapors pass through vent hoses or
tubes to a carbon filled EVAP canister. They are tem-
porarily held in the canister until they can be drawn
into the intake manifold when the engine is running.
The EVAP canister is a feature on all models for
the storage of fuel vapors from the fuel tank.
The hoses used in this system are specially
manufactured. If replacement becomes neces-
sary, it is important to use only fuel resistant
hose.
EVAP CANISTER
A sealed, maintenance free, EVAP canister is used
on all vehicles. On XJ models, the EVAP canister is
located in the engine compartment on the passenger
side frame rail (Fig. 4). On YJ models, the EVAP can-
ister is located in the engine compartment on the
dash panel and below the brake master cylinder (Fig.
5). The EVAP canister is filled with granules of an
activated carbon mixture. Fuel vapors entering the
EVAP canister are absorbed by the charcoal granules.
CANISTER OPERATION
Vacuum is used to control and operate the
EVAP canister. No electrical circuitry is used to
control or operate the EVAP system.
The EVAP canister is equipped with a vacuum con-
trolled purge shutoff switch (orifice) (Figs. 4 or 5)
that controls canister purge operation. The switch is
open when manifold vacuum is applied to it. When
the engine is operating, the EVAP canister purge
function draws fresh air through the top of the can-
ister. This causes the stored vapors to be drawn out
of the canister and into the airstream in the air
cleaner snorkel (Fig. 6).
The air cleaner contains a venturi in the air
cleaner cover used as a purge line vacuum source
(Fig. 6). The venturi effect increases the speed of the
intake air flowing by the slots in the venturi wall.
This creates a low pressure area around the slots.
When the purge shutoff switch is open, vapors from
the canister are drawn through slots and into the air-
stream flowing through the venturi (Fig. 7). The va-
pors pass through the intake manifold into the
engine combustion chambers where they are con-
sumed during engine combustion.
FUEL TANK FILLER TUBE CAP
The fuel tank filler tube cap (fuel tank cap) incor-
porates a two-way pressure/relief valve that is closed
to atmosphere during normal operating conditions.Fig. 4 EVAP Canister LocationÐXJ Models
Fig. 5 EVAP Canister LocationÐYJ Models
25 - 4 EMISSION CONTROL SYSTEMSJ
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The relief valve used in fuel filler caps of all models
is calibrated at a pressure of 10 kPa (1.5 psi) or a
vacuum of 6 kPa (1.8 in. Hg). When the pressure or
vacuum is relieved, the valve returns to the normally
closed position.
CAUTION: The fuel filler cap must be removed prior
to disconnecting any fuel system component.
CRANKCASE VENTILATION SYSTEM
All 2.5L 4 cylinder and 4.0L 6 cylinder engines are
equipped with a Crankcase Ventilation (CCV) system(Figs. 8 or 9). 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 tube
contains a fixed orifice of a calibrated size. It meters
the amount of crankcase vapors drawn out of the en-
gine.
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 en-
gines. It is connected to rear of cover on 2.5L
engines.
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.
Fig. 6 EVAP SystemÐTypical
Fig. 7 Air Cleaner VenturiÐTypical
Fig. 8 CCV SystemÐ2.5L EngineÐTypical
Fig. 9 CCV SystemÐ4.0L EngineÐTypical
JEMISSION CONTROL SYSTEMS 25 - 5
Page 1939 of 2198
PRESSURE RELIEF/ROLLOVER VALVE
All vehicles are equipped with a combination fuel
tank pressure relief and rollover valve (Fig. 10). 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
(Fig. 11) that releases fuel tank pressure when the
pressure increases above the calibrated sealing value.
Refer to the Fuel Tank section of Group 14, Fuel Sys-
tems for removal and installation procedures.
OXYGEN (O2S) SENSOR
For description, operation, diagnosis and removal/
installation procedures of the O2S sensor, refer to
Group 14, Fuel Systems.
Fig. 10 Pressure Relief/Rollover Valve LocationÐ
Typical
Fig. 11 Typical Pressure Relief/Rollover Valve
Operation
25 - 6 EMISSION CONTROL SYSTEMSJ
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COMPONENT REMOVAL/INSTALLATION
INDEX
page page
Air Cleaner Element........................ 7
Coolant Temperature Sensor.................. 7
EVAP Canister............................ 7
Fuel Tank Filler Tube Cap.................... 7Oxygen (O2S) Sensor....................... 7
Powertrain Control Module (PCM).............. 7
Pressure Relief/Rollover Valve................. 7
AIR CLEANER ELEMENT
For removal and installation procedures of both the
air cleaner housing and the air cleaner element, refer
to the Group 14, Fuel System.
COOLANT TEMPERATURE SENSOR
For description, operation, diagnosis and removal/
installation procedures of the engine coolant temper-
ature sensor, refer to Group 14, Fuel Systems.
EVAP CANISTER
On XJ models, the EVAP canister is located in the
engine compartment on the passenger side frame rail
(Fig. 1). On YJ models, the EVAP canister is located
in the engine compartment on the dash panel and be-
low the brake master cylinder (Fig. 2).
REMOVAL/INSTALLATION
(1) Disconnect the vacuum lines at the EVAP can-
ister. Note location of lines before removal.(2) Remove canister retaining strap bolt.
(3) Remove canister from vehicle.
Reverse the procedure for installation.
FUEL TANK FILLER TUBE CAP
If replacement of the fuel filler tube cap (fuel tank
cap) is necessary, it must be replaced with aniden-
tical capto be sure of correct system operation.
OXYGEN (O2S) SENSOR
For description, operation, diagnosis and removal/
installation procedures of the O2S sensor, refer to
Group 14, Fuel Systems.
POWERTRAIN CONTROL MODULE (PCM)
For removal and installation procedures, refer to
Group 14, Fuel Systems.
PRESSURE RELIEF/ROLLOVER VALVE
For removal and installation procedures, refer to
the Fuel Tank section of Group 14, Fuel Systems.
Fig. 1 EVAP CanisterÐXJ Models
Fig. 2 EVAP CanisterÐYJ Models
JEMISSION CONTROL SYSTEMS 25 - 7
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Page 1942 of 2198
CHRYSLER
CORPORATION
SERVICE MANUAL
1995 JEEP
To order the special service tools used and
illustrated, please refer to the instructions on
inside back cover.
NO PART OF THIS PUBLICATION MAY BE
REPRODUCED, STORED IN A RETRIEVAL
SYSTEM, OR TRANSMITTED, IN ANY FORM
OR BY ANY MEANS, ELECTRONIC, ME-
CHANICAL, PHOTOCOPYING, RECORDING,
OR OTHERWISE, WITHOUT THE PRIOR
WRITTEN PERMISSION OF CHRYSLER
CORPORATION.
Chrysler Corporation reserves the right to make changes in design or to
make additions to or improvements in its products without imposing any ob-
ligations upon itself to install them on its products previously manufactured.
Litho in U.S.A. Copyright 1994 Chrysler Corporation 20M0694
NEXT PAGE©
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FOREWORD
The information contained in this service manual has been prepared for the professional automotive tech-
nician involved in daily repair operations. This manual does not cover theory of operation, which is addressed
in service training material. Information describing the operation and use of standard and optional equipment
is included in the Owner 's Manual provided with the vehicle.
Information in this manual is divided into groups. These groups contain general information, diagnosis,
testing, adjustments, removal, installation, disassembly, and assembly procedures for the components. To as-
sist in locating a group title page, use the Group Tab Locator on the following page. The solid bar after the
group title is aligned to a solid tab on the first page of each group. The first page of the group has a contents
section that lists major topics within the group. If you are not sure which Group contains the information you
need, look up the Component/System in the alphabetical index located in the rear of this manual.
A Service Manual Comment form is included at the rear of this manual. Use the form to provide Chrysler
Corporation with your comments and suggestions.
Tightening torques are provided as a specific value throughout this manual. This value represents the
midpoint of the acceptable engineering torque range for a given fastener application. These torque values are
intended for use in service assembly and installation procedures using the correct OEM fasteners. When re-
placing fasteners, always use the same type (part number) fastener as removed.
Chrysler Corporation reserves the right to change testing procedures, specifications, diagnosis, repair
methods, or vehicle wiring at any time without prior notice or incurring obligation.
NOTE: The acronyms, terminology and nomenclature used to identify emissions related components in
this manual may have changed from prior publications. These new terms are in compliance with S.A.E.
recommended practice J1930.
NEXT PAGE©
Page 1944 of 2198
GROUP TAB LOCATOR
Introduction
0Lubrication and Maintenance
2Front Suspension and Axle
3Rear Suspension and Axles
5Brakes
6Clutch
7Cooling System
8Electrical
9Engines
11Exhaust System and Intake Manifold
13Frame and Bumpers
14Fuel System
16Propeller Shafts
19Steering
21Transmission and Transfer Cases
22Wheels and Tires
23Body Components
24Heating and Air Conditioning
25Emission Control Systems
Index
Service Manual Comment Forms (Rear of Manual)