1995 JEEP YJ Fuel system

line. You may encounter fuels containing 3 percent or
more methanol along with other alcohols called cosol-
vents.
Problems that are the result of using methanol/gas-
oline blends are not the responsibility of Chrysler
Corporation. They may not be covered by the vehicle
warranty.
MTBE/ETBE
Gasoline and MTBE (Methyl Tertiary Butyl Ether)
blends are a mixture of unleaded gasoline and up to
15 percent MTBE. Gasoline and ETBE (Ethyl Ter-
tiary Butyl Ether) are blends of gasoline and up to
17 percent ETBE. Gasoline blended with MTBE or
ETBE may be used.
CLEAN AIR GASOLINE
Many gasolines are now being blended that con-
tribute to cleaner air, especially in those areas of the
country where air pollution levels are high. These
new blends provide a cleaner burning fuel and some
are referred to asReformulated Gasoline.
In areas of the country where carbon monoxide lev-
els are high, gasolines are being treated with oxygen-
ated materials such as MTBE, ETBE and ethanol.
Chrysler Corporation supports these efforts toward
cleaner air and recommends the use of these gaso-
lines as they become available.
IGNITION CABLES, DISTRIBUTOR CAP AND
ROTOR
Inspect and test ignition cables, distributor cap and
rotor when the spark plugs are replaced. Oil and
grime should be cleaned from the ignition cables and
distributor cap to avoid possible spark plug fouling.
Mopar Foamy Engine Degreaser or equivalent is rec-
ommended for cleaning the engine compartment. For
proper service and diagnostic procedures refer to
Group 8D, Ignition System.
IGNITION TIMING
The ignition timing for 2.5L and 4.0L engines is
not adjustable. Refer to the specifications listed on
the engine Emission Control Information Label. Re-
fer to Group 25, Emission Control Systems for addi-
tional information.
SPARK PLUGS
Ignition spark plugs should be replaced at the
mileage interval described in the Lubrication and
Maintenance Schedules. Refer to the General Infor-
mation section of this group. For proper service pro-
cedures refer to Group 8D, Ignition Systems.
BATTERY
WARNING: WEAR SAFETY GLASSES, RUBBER
GLOVES AND PROTECTIVE CLOTHING WHEN HAN-DLING/SERVICING A BATTERY. THE BATTERY
ELECTROLYTE CONTAINS SULFURIC ACID AND
WILL CAUSE HARM IF IT CONTACTS SKIN, EYES
OR CLOTHING. IT WILL ALSO DAMAGE PAINTED
(AS WELL AS UN-PAINTED) SURFACES OF A VEHI-
CLE. IF SULFURIC ACID CONTACTS ANY OF
THESE, FLUSH IMMEDIATELY WITH LARGE
AMOUNTS OF WATER. IF SULFURIC ACID CON-
TACTS SKIN OR EYES, GET IMMEDIATE MEDICAL
ATTENTION. DO NOT SMOKE IN THE VICINITY OF A
BATTERY. KEEP OPEN FLAMES AND SPARKS
AWAY FROM BATTERY FILLER CAPS BECAUSE
EXPLOSIVE GAS IS ALWAYS PRESENT.
Inspect battery tray, hold down and terminal con-
nections when other under hood service is performed.
For proper diagnostic procedures refer to Group 8A,
Battery/Starting/Charging System Diagnostics. For
service and cleaning procedures refer to Group 8B,
Battery/Starter Service.
Care should be taken when disposing a bat-
tery after removal from a vehicle. Lead-acid
batteries are highly poisonous and, when indis-
criminately disposed, could create a problem
for the environment. Contact the applicable lo-
cal city or county government agency to deter-
mine where automobile (lead-acid) batteries
can be properly disposed in the local area.
RUBBER AND PLASTIC COMPONENT INSPECTION
CAUTION: Plastic hoses or wire harness covers will
melt or deform when exposed to heat from exhaust
system or engine manifolds.
Position plastic or rubber components away from
moving parts in engine compartment or under vehi-
cle, or damage will result.
Do not allow rubber engine mounts or other com-
ponents to become oil contaminated, repair cause
of oil contamination and clean area.
All rubber and plastic components should be in-
spected when engine compartment or under vehicle
service is performed. When evidence of deterioration
exists, replacement is required. To reduce deteriora-
tion of rubber components, Chrysler Corporation rec-
ommends Mopar Foamy Engine Degreaser or
equivalent be used to clean engine compartment of
oil and road grime.
EMISSION CONTROL SYSTEM
Inspect all emission control components and hoses
when other under hood service is performed. Refer to
emission system Vacuum Hose Label located on the
inside of the hood in the engine compartment and
Group 25, Emission Control Systems for proper ser-
vice procedures.
0 - 20 LUBRICATION AND MAINTENANCEJ

DIAGNOSIS
INDEX
page page
DRB Scan Tool............................ 5
On-Board Diagnostics (OBD).................. 4Preliminary Checks......................... 5
ON-BOARD DIAGNOSTICS (OBD)
FOR CERTAIN COOLING SYSTEM
COMPONENTS
The powertrain control module (PCM) has been
programmed to monitor the certain following cooling
system components:
²If the engine has remained cool for too long a pe-
riod, such as with a stuck open thermostat, a Diag-
nostic Trouble Code (DTC) number 17 can be
observed at the malfunction indicator lamp. This
lamp is displayed on the instrument panel as the
CHECK ENGINE lamp (Figs. 5 or 6).
²If an open or shorted condition has developed in
the relay circuit controlling the electric radiator fan,
a Diagnostic Trouble Code (DTC) number 35 can be
observed at the CHECK ENGINE lamp (XJ models
only).
If the problem is sensed in a monitored circuit of-
ten enough to indicate an actual problem, a DTC is
stored. The DTC will be stored in the PCM memory
for eventual display to the service technician. If theproblem is repaired or ceases to exist, the PCM can-
cels the DTC after 51 engine starts.
Certain criteria must be met for a DTC to be en-
tered into PCM memory. The criteria may be a spe-
cific range of engine rpm, engine temperature and/or
input voltage to the PCM.
A DTC indicates that the PCM has recognized an
abnormal signal in a circuit or the system. A DTC
may indicate the result of a failure, but never iden-
tify the failed component directly.
It is possible that a DTC for a monitored circuit
may not be entered into memory even though a mal-
function has occurred. Refer to On-Board Diagnostics
(OBD) in Group 14, Fuel Systems for additional DTC
information.
ACCESSING DIAGNOSTIC TROUBLE CODES
A stored Diagnostic Trouble Code (DTC) can be dis-
played by cycling the ignition key On-Off-On-Off-On
within three seconds and observing the malfunction
indicator lamp. This lamp is displayed on the instru-
ment panel as the CHECK ENGINE lamp (Figs. 5 or
6).
They can also be displayed through the use of the
Diagnostic Readout Box (DRB) scan tool. The DRB
connects to the data link connector in the engine
compartment (Figs. 7 or 8). For operation of the
DRB, refer to the appropriate Powertrain Diagnostic
Procedures service manual.
Fig. 5 Check Engine LampÐXJ ModelsÐTypical
Fig. 6 Check Engine LampÐYJ ModelsÐTypical
7 - 4 COOLING SYSTEM DIAGNOSISJ

temperature, coolant is allowed to flow to the radia-
tor. This provides quick engine warmup and overall
temperature control.
An arrow plus the wordUPis stamped on the
front flange next to the air bleed. The wordsTO
RADare stamped on one arm of the thermostat.
They indicate the proper installed position.
The same thermostat is used for winter and sum-
mer seasons. An engine should not be operated with-
out a thermostat, except for servicing or testing.
Operating without a thermostat causes other prob-
lems. These are: longer engine warmup time, unreli-
able warmup performance, increased exhaust
emissions and crankcase condensation. This conden-
sation can result in sludge formation.
CAUTION: Do not operate an engine without a ther-
mostat, except for servicing or testing.
ON-BOARD DIAGNOSTICS
XJ and YJ models are equipped with On-Board Di-
agnostics for certain cooling system components. Re-
fer to On-Board Diagnostics (OBD) in the Diagnosis
section of this group for additional information. If the
powertrain control module (PCM) detects low engine
coolant temperature, it will record a Diagnostic Trou-
ble Code (DTC) in the PCM memory. The DTC num-
ber for low coolant temperature is 17. Do not change
a thermostat for lack of heat as indicated by the in-
strument panel gauge or heater performance unless a
DTC number 17 is present. Refer to the Diagnosis
section of this group for other probable causes. For
other DTC numbers, refer to On-Board Diagnostics
in the General Diagnosis section of Group 14, Fuel
Systems.
The DTC can also be accessed through the DRB
scan tool. Refer to the appropriate Powertrain Diag-
nostic Procedures manual for diagnostic information
and operation of the DRB scan tool.
REMOVAL
WARNING: DO NOT LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND PRES-
SURIZED. SERIOUS BURNS FROM THE COOLANT
CAN OCCUR.
DO NOT WASTE reusable coolant. If the solution
is clean, drain the coolant into a clean container for
reuse.
(1) Drain the coolant from the radiator until the
level is below the thermostat housing.
WARNING: CONSTANT TENSION HOSE CLAMPS
ARE USED ON MOST COOLING SYSTEM HOSES.
WHEN REMOVING OR INSTALLING, USE ONLY
TOOLS DESIGNED FOR SERVICING THIS TYPE OF
CLAMP, SUCH AS SPECIAL CLAMP TOOL (NUMBER
6094) (FIG. 15). SNAP-ON CLAMP TOOL (NUMBER
HPC-20) MAY BE USED FOR LARGER CLAMPS. AL-
WAYS WEAR SAFETY GLASSES WHEN SERVICING
CONSTANT TENSION CLAMPS.
CAUTION: A number or letter is stamped into the
tongue of constant tension clamps (Fig. 16). If re-
placement is necessary, use only an original equip-
ment clamp with matching number or letter.
(2) Remove radiator upper hose and heater hose at
thermostat housing.
(3) Disconnect wiring connector at engine coolant
temperature sensor.
(4) Remove thermostat housing mounting bolts,
thermostat housing, gasket and thermostat (Fig. 17).
Discard old gasket.
(5) Clean the gasket mating surfaces.
Fig. 13 XJ Models with 4.0L 6-Cylinder EngineÐ
Without A/C
Fig. 14 XJ Models With 4.0L 6-Cylinder EngineÐ
With A/C
7 - 18 COOLING SYSTEM SERVICE PROCEDURESJ

(5) Be sure that the air conditioner (if equipped) is
turned off.
WARNING: USE EXTREME CAUTION WHEN THE
ENGINE IS OPERATING. DO NOT STAND IN A DI-
RECT LINE WITH THE FAN. DO NOT PUT YOUR
HANDS NEAR THE PULLEYS, BELTS OR FAN. DO
NOT WEAR LOOSE CLOTHING.
(6) Start the engine and operate at 2400 rpm.
Within ten minutes the air temperature (indicated on
the dial thermometer) should be up to 88É C (190É F).
Fan driveengagementshould have started to occur
at between 74É to 82É C (165É to 180É F). Engage-
ment is distinguishable by a definiteincreasein fan
flow noise (roaring). The timing light also will indi-
cate an increase in the speed of the fan.
(7) When the air temperature reaches 88É C (190É
F), remove the plastic sheet. Fan drivedisengage-
mentshould have started to occur at between 57É to
79É C (135É to 175É F). A definitedecreaseof fan
flow noise (roaring) should be noticed. If not, replace
the defective viscous fan drive unit.
VISCOUS FAN DRIVE REMOVAL/INSTALLATION
Refer to the previous section on Cooling System
Fan for removal and installation procedures of the
viscous drive unit.
Viscous Fan Drive Fluid Pump Out Require-
ment:After installing anewviscous fan drive, bring
the engine speed up to approximately 2000 rpm and
hold for approximately two minutes. This will ensure
proper fluid distribution within the drive.
AUXILIARY ELECTRIC COOLING FANÐXJ MODELS
WITH 4.0L 6-CYLINDER ENGINE
OPERATION
XJ models equipped with a 4.0L 6-cylinder engine
may also have an auxiliary electrical cooling fan.
This is with models that have air conditioning and/or
heavy duty cooling. The fan is controlled by the cool-
ing fan relay, which is located in the power distribu-
tion center (PDC). For the location of relay within
the PDC (Fig. 41), refer to the label on PDC cover.
When coolant temperature is above 88ÉC (190ÉF),
the powertrain control module (PCM) provides a
ground path for the fan relay. This ground is pro-
vided through pin/connector #31 of the PCM 60-way
connector. Battery voltage is then applied to the fan
through the relay. When coolant temperature is be-
low 88ÉC (190ÉF), the PCM opens the ground path to
the relay. This will prevent the cooling fan from be-
ing energized.
Whenever the air conditioning is operated, the
PCM engages the auxiliary cooling fan. It provides aground path to the cooling fan relay. This ground is
provided through pin/connector #31 of the PCM 60-
way connector.
DIAGNOSIS AND RELAY TESTING
The powertrain control module (PCM) will enter a
diagnostic trouble code (DTC) number 35 in memory
if it detects a problem in the auxiliary cooling fan re-
lay or circuit. This will be read as a flashing signal
at the instrument panel mounted Malfunction Indica-
tor Lamp (displayed on the instrument panel as the
CHECK ENGINE lampÐfigure 42). Refer to On-
Board Diagnostics in Group 14, Fuel Systems for in-
formation on accessing a DTC.
The DTC can also be accessed through the DRB
scan tool. Refer to the appropriate Powertrain Diag-
Fig. 41 PDCÐXJ Models
Fig. 42 Check Engine LampÐXJ ModelsÐTypical
JCOOLING SYSTEM SERVICE PROCEDURES 7 - 35

nostic Procedures manual for diagnostic information
and operation of the DRB scan tool.
To test operation of the fan relay only, refer to Re-
laysÐOperation/Testing. This can be found in Group
14, Fuel Systems.
REMOVAL
The auxiliary cooling fan is attached to the radia-
tor upper crossmember behind the radiator.
(1) Remove the two fan mounting bolts from radi-
ator upper crossmember (Fig. 43).
(2) Disconnect the electric fan connector.
(3) Lift fan straight up and out of vehicle.
INSTALLATION
(1) Align lower retaining tabs of fan shroud with
slots in bracket at bottom of radiator. Push fan down
into position.
(2) Tighten the mounting bolts to 4 Nzm (31 in.
lbs.) torque.
(3) Connect auxiliary cooling fan electrical connec-
tor.
TRANSMISSION OIL COOLERS
WATER-TO-OIL COOLER
All models equipped with an automatic transmis-
sion are equipped with a transmission oil cooler
mounted internally within the radiator tank. This in-
ternal cooler is supplied as standard equipment on
all models equipped with an automatic transmission.
Transmission oil is cooled when it passes through
this separate cooler. In case of a leak in the internalradiator mounted transmission oil cooler, engine cool-
ant may become mixed with transmission fluid or
transmission fluid may enter engine cooling system.
Both cooling system and transmission should be
drained and inspected if the internal radiator
mounted transmission cooler is leaking.
Also refer to the section on Transmission Air-to-Oil
Coolers. This auxiliary air-to-oil cooler is an option
on most engine packages.
REPLACING WATER-TO-OIL COOLER IN
RADIATOR SIDE TANK
The internal transmission oil cooler located within
the radiator is not serviceable. If it requires service,
the radiator must be replaced.
Once the repaired or replacement radiator has
been installed, fill the cooling system and inspect for
leaks. Refer to the Refilling Cooling System and Test-
ing Cooling System For Leaks sections in this group.
If the transmission operates properly after repairing
the leak, drain the transmission and remove the
transmission oil pan. Inspect for sludge and/or rust.
Inspect for a dirty or plugged inlet filter. If none of
these conditions are found, the transmission and
torque convertor may not require reconditioning. Re-
fer to Group 21 for automatic transmission servicing.
AIR-TO-OIL COOLER
An auxiliary air-to-oil transmission oil cooler is
available with most engine packages.
On XJ and YJ models, the cooler is located in front
of the radiator or A/C condenser (if equipped) and be-
hind the grill (Figs. 44, 45 or 46). It is mounted to
the front frame crossmember.
Fig. 43 Auxiliary Cooling FanÐRemove/InstallÐ
Typical
Fig. 44 Auxiliary Air-To-Oil CoolerÐYJ Models
7 - 36 COOLING SYSTEM SERVICE PROCEDURESJ

USING ON-BOARD DIAGNOSTIC SYSTEM
GENERAL INFORMATION
The Powertrain Control Module (PCM) monitors
critical input and output circuits of the charging sys-
tem, making sure they are operational. A Diagnostic
Trouble Code (DTC) is assigned to each input and
output circuit monitored by the OBD system. Some
circuits are checked continuously and some are
checked only under certain conditions.
If the OBD system senses that a monitored circuit
is bad, it will put a DTC into electronic memory. The
DTC will stay in electronic memory as long as the
circuit continues to be bad. The PCM is programmed
to clear the memory after 50 engine starts, if the
problem does not occur again.
DIAGNOSTIC TROUBLE CODES
Diagnostic Trouble Codes (DTC) are two-digit num-
bers flashed on the malfunction indicator (Check En-
gine) lamp that identify which circuit is bad. A DTC
description can also be read using the DRB scan tool.
Refer to Group 14 - Fuel Systems for more informa-
tion.
A DTC does not identify which component in a cir-
cuit is bad. Thus, a DTC should be treated as a
symptom, not as the cause for the problem. In some
cases, because of the design of the diagnostic test
procedure, a DTC can be the reason for another DTCto be set. Therefore, it is important that the test pro-
cedures be followed in sequence, to understand what
caused a DTC to be set.
See Generator Diagnostic Trouble Code chart for
DTC's which apply to the charging system. Refer to
the Powertrain Diagnostic Procedures manual to di-
agnose an on-board diagnostic system trouble code.
RETRIEVING DIAGNOSTIC TROUBLE CODES
To start this function, cycle the ignition switch ON-
OFF-ON-OFF-ON within 5 seconds. This will cause
any DTC stored in the PCM memory to be displayed.
The malfunction indicator (Check Engine) lamp will
display a DTC by flashing on and off. There is a
short pause between flashes and a longer pause be-
tween digits. All DTC's displayed are two-digit num-
bers, with a four-second pause between codes.
An example of a DTC is as follows:
(1) Lamp on for 2 seconds, then turns off.
(2) Lamp flashes 4 times pauses and then flashes 1
time.
(3) Lamp pauses for 4 seconds, flashes 4 times,
pauses, then flashes 7 times.
The two DTC's are 41 and 47. Any number of
DTC's can be displayed, as long as they are in mem-
ory. The lamp will flash until all stored DTC's are
displayed (55 = end of test).
GENERATOR DIAGNOSTIC TROUBLE CODE
8A - 22 BATTERY/STARTING/CHARGING SYSTEMS DIAGNOSTICSJ

STARTER RELAY REMOVE/INSTALL
(1) Disconnect battery negative cable.
(2) Remove starter relay by unplugging unit from
PDC (Fig. 15 or 16).(3) Install starter relay by aligning relay terminals
with cavities in PDC and plugging relay in.
(4) Connect negative cable to battery.
(5) Test relay operation.
GENERATOR
GENERAL INFORMATION
This section covers generator service procedures
only. For generator or charging system diagnosis, re-
fer to Group 8A - Battery/Starting/Charging Systems
Diagnostics.
The generator is belt-driven by the engine. All en-
gines use serpentine drive. The generator is serviced
only as a complete assembly. If the generator fails for
any reason, the entire assembly must be replaced.
Two generator output ratings are available, de-
pending upon optional equipment. Be certain that
the replacement generator has the same output rat-
ing as the original unit. Refer to Group 8A - Battery/
Starting/Charging Systems Diagnostics and see
Specifications.
The generator field control (voltage regulator) cir-
cuitry is internal to the Powertrain Control Module
(PCM). If faulty, the entire PCM must be replaced.
Refer to Group 14 - Fuel System for PCM service
procedure.
GENERATOR REMOVE/INSTALLÐLEFT-HAND
DRIVE
WARNING: DISCONNECT NEGATIVE CABLE FROM
BATTERY BEFORE REMOVING BATTERY OUTPUT
WIRE FROM GENERATOR. FAILURE TO DO SO
CAN RESULT IN INJURY.
ALL WITH 2.5L AND YJ WITH 4.0L
(1) Disconnect battery negative cable.
(2) Remove generator drive belt. Refer to Group 7 -
Cooling System for procedure.
(3) Remove generator battery output terminal nut,
2 field terminal nuts, ground and harness holddown
nuts (Fig. 17). Remove wire connector assembly.
(4) Remove 2 generator mounting bolts and remove
generator from vehicle.
(5) Reverse removal procedure to install. Torque
generator hardware as shown in Specifications.
CAUTION: Never force a belt over a pulley rim us-
ing a screwdriver. The synthetic fiber of the belt can
be damaged.
Fig. 15 Power Distribution CenterÐXJFig. 16 Power Distribution CenterÐYJ
8B - 6 BATTERY/STARTER/GENERATOR SERVICEJ

IGNITION SYSTEMS
CONTENTS
page page
COMPONENT IDENTIFICATION/SYSTEM
OPERATION........................... 1
COMPONENT REMOVAL/INSTALLATION...... 17
DIAGNOSTICS/SERVICE PROCEDURES....... 6IGNITION SWITCHÐXJ MODELS........... 26
IGNITION SWITCHÐYJ MODELS........... 29
SPECIFICATIONS........................ 32
COMPONENT IDENTIFICATION/SYSTEM OPERATION
INDEX
page page
Automatic Shutdown (ASD) Relay.............. 1
Camshaft Position Sensor.................... 2
Crankshaft Position Sensor................... 3
Distributors............................... 4
Engine Coolant Temperature Sensor............ 5
General Information........................ 1Ignition Coil.............................. 4
Intake Manifold Air Temperature Sensor.......... 5
Manifold Absolute Pressure (MAP) Sensor........ 5
Oxygen (O2S) Sensor....................... 5
Powertrain Control Module (PCM).............. 5
Throttle Position Sensor..................... 5
GENERAL INFORMATION
Throughout this group, references are made to par-
ticular vehicle models by alphabetical designation
(XJ or YJ) or by the particular vehicle nameplate. A
chart showing a breakdown of alphabetical designa-
tions is included in the Introduction group at the be-
ginning of this manual.
This section of the group, Component Identifica-
tion/System Operation, will discuss ignition system
operation and will identify ignition system compo-
nents.
For diagnostic procedures and adjustments, refer to
the Diagnostics/Service Procedures section of this
group.
For removal and installation of ignition system
components, refer to the Component Removal/Instal-
lation section of this group.
For other useful information, refer to On-Board Di-
agnostics in the General Diagnosis sections of Group
14, Fuel System in this manual.
For operation of the DRB Scan Tool, refer to the
appropriate Powertrain Diagnostic Procedures ser-
vice manual.
An Ignition specifications section is included at the
end of this group. A general Maintenance Schedule
(mileage intervals) for ignition related items can be
found in Group 0, Lubrication and Maintenance. This
schedule can also be found in the Owners Manual.
IGNITION SYSTEMS
A multi-port, fuel injected engine is used on all
models. The ignition system is controlled by the pow-
ertrain control module (PCM) on all engines. The
PCM was formerly referred to as the SBEC or engine
controller.
The ignition system consists of:
²Spark plugs
²Ignition coil
²Secondary ignition cables
²Distributor (contains rotor and camshaft position
sensor)
²Powertrain control module (PCM)
²Crankshaft position sensor
AUTOMATIC SHUTDOWN (ASD) RELAY
The automatic shutdown (ASD) relay is located in
the power distribution center (PDC) near the battery
(Fig. 1 or 2). As one of its functions, it will supply
battery voltage to the ignition coil.
The ground circuit for the ASD relay is controlled
by the powertrain control module (PCM). This is
done through pin/cavity number 51 of the PCM 60-
way connector. The PCM then regulates ASD relay
operation by switching this ground circuit on-and-off.
Also refer to Ignition Coil for additional informa-
tion.
JIGNITION SYSTEMS 8D - 1