1995 JEEP YJ wheel

VISCOUS FAN DRIVE
DESCRIPTION AND OPERATION
Also refer to the previous section on Cooling Sys-
tem Fans.
The thermal viscous fan drive (Fig. 38 or 39) is a
silicone-fluid-filled coupling used to connect the fan
blades to either the engine or the water pump shaft.
The coupling allows the fan to be driven in a normal
manner. This is done at low engine speeds while lim-
iting the top speed of the fan to a predetermined
maximum level at higher engine speeds.
A thermostatic bimetallic spring coil is located on
the front face of the viscous fan drive unit (a typical
viscous unit is shown in figure 40). This spring coil
reacts to the temperature of the radiator discharge
air. It engages the viscous fan drive for higher fan
speed if the air temperature from the radiator rises
above a certain point. Until additional engine cooling
is necessary, the fan will remain at a reduced rpm re-
gardless of engine speed.
Only when sufficient heat is present, will the vis-
cous fan drive engage. This is when the air flowing
through the radiator core causes a reaction to the bi-
metallic coil. It then increases fan speed to provide
the necessary additional engine cooling.
Once the engine has cooled, the radiator discharge
temperature will drop. The bimetallic coil again re-
acts and the fan speed is reduced to the previous dis-
engaged speed.
CAUTION: Engines equipped with serpentine drive
belts have reverse rotating fans and viscous fan
drives. They are marked with the word REVERSE to
designate their usage. Installation of the wrong fan
or viscous fan drive can result in engine overheat-
ing.CAUTION: If the viscous fan drive is replaced be-
cause of mechanical damage, the cooling fan
blades should also be inspected. Inspect for fatigue
cracks, loose blades, or loose rivets that could
have resulted from excessive vibration. Replace fan
blade assembly if any of these conditions are
found. Also inspect water pump bearing and shaft
assembly for any related damage due to a viscous
fan drive malfunction.
NOISE
It is normal for fan noise to be louder (roar-
ing) when:
²The underhood temperature is above the engage-
ment point for the viscous drive coupling. This may
occur when ambient (outside air temperature) is very
high.
²Engine loads and temperatures are high such as
when towing a trailer.
²Cool silicone fluid within the fan drive unit is be-
ing redistributed back to its normal disengaged
(warm) position. This can occur during the first 15
seconds to one minute after engine start-up on a cold
engine.
LEAKS
Viscous fan drive operation is not affected by small
oil stains near the drive bearing. If leakage appears
excessive, replace the fan drive unit.
TESTING
If the fan assembly free-wheels without drag (the
fan blades will revolve more than five turns when
spun by hand), replace the fan drive. This spin test
must be performed when the engine is cool.
For the following test, the cooling system must be
in good condition. It also will ensure against exces-
sively high coolant temperature.
WARNING: BE SURE THAT THERE IS ADEQUATE
FAN BLADE CLEARANCE BEFORE DRILLING.
(1) Drill a 3.18-mm (1/8-in) diameter hole in the
top center of the fan shroud.
(2) Obtain a dial thermometer with an 8 inch stem
(or equivalent). It should have a range of -18É-to-
105ÉC (0É-to-220É F). Insert thermometer through the
hole in the shroud. Be sure that there is adequate
clearance from the fan blades.
(3) Connect a tachometer and an engine ignition
timing light (timing light is to be used as a strobe
light).
(4) Block the air flow through the radiator. Secure
a sheet of plastic in front of the radiator (or air con-
ditioner condenser). Use tape at the top to secure the
plastic and be sure that the air flow is blocked.
Fig. 40 Typical Viscous Fan Drive
7 - 34 COOLING SYSTEM SERVICE PROCEDURESJ

STARTING SYSTEM
GENERAL INFORMATION
The starting system (Fig. 1) consists of:
²ignition switch
²starter relay
²park/neutral position switch (automatic transmis-
sion)
²wiring harness and connections
²battery
²starter with an integral solenoid.
Following is a general description of the major
starting system components. Refer to Group 8W -
Wiring Diagrams for complete circuit descriptions
and diagrams.
These components form 2 separate circuits. A high-
amperage feed circuit that feeds the starter up to
300+ amps, and a low-amperage control circuit that
operates on less than 20 amps.
Battery voltage is supplied through the low-amper-
age control circuit to the coil battery terminal of the
starter relay when the ignition switch is turned to
the START position.
If the vehicle is equipped with an automatic trans-
mission, the park/neutral position switch provides a
ground path to the starter relay coil ground terminal.
This switch provides ground only with the transmis-
sion in NEUTRAL or PARK. If the vehicle is
equipped with a manual transmission, the starter re-
lay coil ground terminal is always grounded.
With the starter relay coil now energized, the nor-
mally open relay contacts close. The relay contacts
connect the relay common feed terminal to the relay
normally open terminal. The closed relay contacts en-
ergize the starter solenoid coil windings.
The energized solenoid coils pull-in and hold-in the
solenoid plunger. The solenoid plunger pulls the shiftlever in the starter. This engages the starter overrun-
ning clutch and pinion gear with the flywheel/drive
plate ring gear.
As the solenoid plunger reaches the end of its
travel, the solenoid contact disc completes the high-
amperage starter feed circuit. Current now flows be-
tween the solenoid battery terminal and the starter
motor, energizing the starter.
Once the engine starts, the overrunning clutch pro-
tects the starter from damage by allowing the starter
pinion gear to spin faster than the pinion shaft.
When the driver releases the ignition switch to the
ON position the starter relay coil is de-energized.
This causes the relay contacts to open. When the re-
lay contacts open, the starter solenoid coil is de-ener-
gized.
When the solenoid coil is de-energized, the solenoid
plunger return spring returns the plunger to its re-
laxed position. This causes the contact disc to open
the starter feed circuit, and the shift lever to disen-
gage the overrunning clutch and pinion gear from the
ring gear.
The starter motor and solenoid are serviced only as
a complete assembly. If either component fails, the
entire assembly must be replaced.
DIAGNOSIS
Before removing any unit from the starting system
for repair, perform the following inspections:
INSPECTION
BATTERY INSPECTION
To determine condition of the battery, see Battery
in this group.
WIRING INSPECTION
Inspect wiring for damage. Inspect all connections
at:
²starter solenoid
²park/neutral position switch (automatic transmis-
sion)
²ignition switch
²starter relay
²battery (including all ground connections).
Clean, tighten and repair all connections as re-
quired.
SOLENOID, RELAY AND SWITCH INSPECTIONS
Inspect the solenoid, relay and ignition switch to
determine their condition. Also, if equipped with au-
tomatic transmission, inspect condition of the park/
neutral position switch. Testing information can be
found in the following pages.
Fig. 1 Starting System Components (Typical)
JBATTERY/STARTING/CHARGING SYSTEMS DIAGNOSTICS 8A - 11

IGNITION SWITCH TEST
Refer to Group 8D - Ignition Systems for testing
and service of this component.
PARK/NEUTRAL POSITION SWITCH TEST
Refer to Group 21 - Transmission and Transfer
Case for testing and service of this component.
2.5L STARTER NOISE DIAGNOSIS
See Starter Noise Diagnosis chart. If the complaint
is similar to Conditions 1 and 2 in chart, correction
can be achieved by shimming starter according to the
following procedures:
Disconnect the battery negative cable to pre-
vent inadvertent starting of engine.
(1) If the complaint is similar to Condition 1, the
starter must be moved toward the flywheel/drive
plate ring gear by removing shims (Fig. 11).
Shim thickness is 0.381 mm (0.015 in.) and
shims may be stacked if required.
(2) If the complaint is similar to Condition 2, the
starter must be moved away from the flywheel/drive
plate ring gear. This is done by installing shim(s)
across both mounting pads. More than one shim may
be required.
This is generally a condition that causes bro-
ken flywheel/drive plate ring gear teeth or bro-
ken starter housings.
STARTER NOISE DIAGNOSIS
Fig. 11 Starter Shim
8A - 16 BATTERY/STARTING/CHARGING SYSTEMS DIAGNOSTICSJ

CAUTION: Be certain that battery cables are con-
nected to the correct battery terminals. Reverse po-
larity can damage electrical components.
(12) Place oiled felt washer on battery positive ter-
minal post.
(13) Install and tighten battery positive cable ter-
minal clamp. Then install and tighten negative cableterminal clamp. Both cable clamp bolts require
torque of 8.5 Nzm (75 in. lbs.).
(14) Apply a thin coating of petroleum jelly or
chassis grease to cable terminals and battery posts.
STARTER AND STARTER RELAY
GENERAL INFORMATION
This section covers starter and starter relay service
procedures only. For diagnostic procedures, refer to
Group 8A - Battery/Starting/Charging Systems Diag-
nostics. Service procedures for other starting system
components can be found as follows:
²battery - see Battery, in this group
²ignition switch - refer to Group 8D - Ignition Sys-
tems
²park/neutral position switch (automatic transmis-
sion) - refer to Group 21 - Transmission and Transfer
Case
²wiring harness and connectors - refer to Group 8W
- Wiring Diagrams.
STARTER
The starter motor incorporates several features to
create a reliable, efficient, compact and lightweight
unit. A planetary gear system (intermediate trans-
mission) is used between the electric motor and pin-
ion gear. This feature makes it possible to reduce the
dimensions of the starter. At the same time, it allows
higher armature rotational speed and delivers in-
creased torque through the pinion gear to the fly-
wheel or drive plate ring gear.
The use of a permanent magnet field also reduces
starter size and weight. This field consists of six
high-strength permanent magnets. The magnets are
aligned according to their polarity and are perma-
nently fixed in the starter field frame.
The starter motors for all engines are activated by
a solenoid mounted to the overrunning clutch hous-
ing. However, the starter motor/solenoid are serviced
only as a complete assembly. If either component
fails, the entire assembly must be replaced.
This unit is highly sensitive to hammering, shocks
and external pressure.
CAUTION: The starter motor MUST NOT BE
CLAMPED in a vise by the starter field frame. Doing
so may damage the magnets. It may be clamped by
the mounting flange ONLY.CAUTION: Do not connect starter motor incorrectly
when tests are being performed. The permanent
magnets may be damaged and rendered unservice-
able.
STARTER RELAY
The starter relay is an International Standards Or-
ganization (ISO) type relay, and is located in the
Power Distribution Center (PDC). Refer to underside
of PDC cover for relay location.
STARTER REMOVE/INSTALLÐ2.5L
XJ MODELS
(1) Disconnect battery negative cable.
(2) Remove exhaust clamp from bracket (Fig. 11).
(3) Remove nut and bolt from forward end of brace
rod (automatic transmission only).
Fig. 11 Exhaust Clamp and Brace Remove (XJÐ
2.5L)
8B - 4 BATTERY/STARTER/GENERATOR SERVICEJ

CRANKSHAFT POSITION SENSOR
The crankshaft position sensor is mounted to the
transmission bellhousing at the left/rear side of the
engine block (Figs. 5, 6 or 7).
Engine speed and crankshaft position are provided
through the crankshaft position sensor. The sensor
generates pulses that are the input sent to the pow-
ertrain control module (PCM). The PCM interprets
the sensor input to determine the crankshaft posi-
tion. The PCM then uses this position, along with
other inputs, to determine injector sequence and ig-
nition timing.
The sensor is a hall effect device combined with an
internal magnet. It is also sensitive to steel within a
certain distance from it.
SENSOR OPERATION
The flywheel/drive plate has groups of four notches
at its outer edge. On 4.0L 6-cylinder engines there
are three sets of notches (Figs. 9 or 10). On 2.5L
4-cylinder engines there are two sets of notches (Fig.
8).
The notches cause a pulse to be generated when
they pass under the sensor. The pulses are the input
to the PCM. For each engine revolution there are two
Fig. 5 Crankshaft Position SensorÐ2.5L 4-Cyl.
EngineÐTypical
Fig. 6 Crankshaft Position SensorÐ4.0L 6-Cyl.
EngineÐAll Except YJ models With Automatic
Transmission
Fig. 7 Crankshaft Position SensorÐ4.0L 6-Cyl.
EngineÐYJ models With Automatic Transmission
Fig. 8 Sensor OperationÐ2.5L 4-Cyl. Engine
JIGNITION SYSTEMS 8D - 3

IGNITION SECONDARY CIRCUIT DIAGNOSIS
CHECKING FOR SPARK
CAUTION: When disconnecting a high voltage cable
from a spark plug or from the distributor cap, twist
the rubber boot slightly (1/2 turn) to break it loose
(Fig. 12). Grasp the boot (not the cable) and pull it
off with a steady, even force.
(1) Disconnect the ignition coil secondary cable
from center tower of the distributor cap. Hold the ca-
ble terminal approximately 12 mm (1/2 in.) from a
good engine ground (Fig. 13).
WARNING: BE VERY CAREFUL WHEN THE ENGINE
IS CRANKING. DO NOT PUT YOUR HANDS NEAR
THE PULLEYS, BELTS OR THE FAN. DO NOT WEAR
LOOSE FITTING CLOTHING.
(2) Rotate (crank) the engine with the starter mo-
tor and observe the cable terminal for a steady arc. If
steady arcing does not occur, inspect the secondary
coil cable. Refer to Spark Plug Cables in this group.
Also inspect the distributor cap and rotor for cracksor burn marks. Repair as necessary. If steady arcing
occurs, connect ignition coil cable to the distributor
cap.
(3) Remove a cable from one spark plug.
(4) Using insulated pliers, hold the cable terminal
approximately 12 mm (1/2 in.) from the engine cylin-
der head or block while rotating the engine with the
starter motor. Observe the spark plug cable terminal
for an arc. If steady arcing occurs, it can be expected
that the ignition secondary system is operating cor-
rectly.(note that if the ignition coil cable is re-
moved for this test, instead of a spark plug
cable, the spark intensity will be much higher.)
If steady arcing occurs at the spark plug cables, but
the engine will not start, connect the DRB scan tool.
Refer to the Powertrain Diagnostic Procedures ser-
vice manual.
FAILURE TO START TEST
To prevent unnecessary diagnostic time and wrong
test results, the previous Checking For Spark test
should be performed prior to this test.
WARNING: SET PARKING BRAKE OR BLOCK THE
DRIVE WHEELS BEFORE PROCEEDING WITH THIS
TEST.
(1) Unplug the ignition coil harness connector at
the coil (Fig. 14).
(2) Connect a set of small jumper wires (18 gauge
or smaller) between the disconnected harness termi-
nals and the ignition coil terminals. To determine po-
larity at connector and coil, refer to the Wiring
Diagrams section.
(3) Attach one lead of a voltmeter to the positive
(12 volt) jumper wire. Attach the negative side of
voltmeter to a good ground. Determine that sufficient
battery voltage (12.4 volts) is present for the starting
and ignition systems.
Fig. 12 Cable Removal
Fig. 13 Checking for SparkÐTypical
Fig. 14 Coil Harness ConnectorÐTypical (4.0L
Shown)
8D - 10 IGNITION SYSTEMSJ

CAUTION: On some models, two bolts are used to
secure the sensor to the transmission. These bolts
are specially machined to correctly space the unit
to the flywheel. Do not attempt to install any other
bolts.
(3) Connect the electrical connector to the sensor.
(4) Install clip on sensor wire harness.
(5) Install clip over fuel rail mounting stud. Install
clip mounting nut.
INSTALLATIONÐYJ MODELS WITH 4.0L
6-CYLINDER ENGINE AND AUTOMATIC
TRANSMISSION
(1) Install the sensor into the access hole on the
transmission.
(2) Install sensor mounting bolt (Fig. 6).
(3) Tighten sensor mounting bolt to 6-to-8 Nzm (50-
to-70 in. lbs.) torque.
(4) Connect the electrical connector to sensor.
(5) Install the clip to sensor wire harness.
(6) Install clip over fuel rail mounting stud. Install
clip mounting nut.
ENGINE COOLANT TEMPERATURE SENSOR
For an operational description, diagnosis and re-
moval/installation procedures, refer to Group 14,
Fuel System.
DISTRIBUTOR
GENERAL INFORMATION
All distributors contain an internal oil seal that
prevents oil from entering the distributor housing.
The seal is not serviceable.
Factory replacement distributors are equipped with
a plastic alignment pin already installed. The pin is
located in an access hole on the bottom of the distrib-
utor housing (Fig. 7). It is used to temporarily lock
the rotor to the cylinder number 1 position during in-
stallation. The pin must be removed after installing
the distributor.
The camshaft position sensor is located in the dis-
tributor on all engines (Fig. 8). For removal/installa-
tion procedures, refer to Camshaft Position Sensor.
Distributor removal is not necessary for sensor re-
moval.
Refer to figure 8 for an exploded view of the dis-
tributor.
A fork with a slot is supplied on the bottom of the
distributor housing where the housing base seats
against the engine block (Fig. 8). The centerline of
the slot aligns with the distributor holddown bolt
hole in the engine block. Because of the fork, the dis-
tributor cannot be rotated. Distributor rotation is not
necessary as all ignition timing requirements are
handled by the powertrain control module (PCM).The position of the distributor determines fuel syn-
chronization only. It does not determine ignition tim-
ing.
Do not attempt to modify this fork to attain
ignition timing.
Fig. 7 Plastic Alignment Pin
Fig. 8 DistributorÐ2.5L Or 4.0L EnginesÐTypical
JIGNITION SYSTEMS 8D - 19

motion. Never pull directly on the cable. Internal
damage to cable will result.
(2) Prior to removing the spark plug, spray com-
pressed air around the spark plug hole and the area
around the spark plug. This will help prevent foreign
material from entering the combustion chamber.
(3) Remove the spark plug using a quality socket
with a rubber or foam insert.
(4) Inspect the spark plug condition. Refer to
Spark Plugs in the Diagnostics/Service Procedures
section of this group.
PLUG CLEANING
The plugs may be cleaned using commercially
available spark plug cleaning equipment. After clean-
ing, file the center electrode flat with a small point
file or jewelers file before adjusting gap.
CAUTION: Never use a motorized wire wheel brush
to clean the spark plugs. Metallic deposits will re-
main on the spark plug insulator and will cause
plug misfire.
PLUG GAP ADJUSTMENT
Check the spark plug gap with a gap gauge tool. If
the gap is not correct, adjust it by bending the
ground electrode (Fig. 20).Never attempt to adjust
the gap by bending the center electrode.
SPARK PLUG GAP
²2.5L 4-Cylinder Engine Spark Plug Gap: .89 mm
(.035 in).
²4.0L 6-Cylinder Engine Spark Plug Gap: .89 mm
(.035 in).
PLUG INSTALLATION
Always tighten spark plugs to the specified torque.
Over tightening can cause distortion. This may result
in a change in the spark plug gap, or a cracked por-
celain insulator.
When replacing the spark plug and ignition coil ca-
bles, route the cables correctly and secure them in
the appropriate retainers. Failure to route the cables
properly can cause the radio to reproduce ignition
noise. It could cause cross ignition of the spark plugs,
or short circuit the cables to ground.
(1) Start the spark plug into the cylinder head by
hand to avoid cross threading.
(2) Tighten the spark plugs to 35-41 Nzm (26-30 ft.
lbs.) torque.
(3) Install spark plug cables over spark plugs.
SPARK PLUG SECONDARY CABLES
CAUTION: When disconnecting a high voltage cable
from a spark plug or from the distributor cap, twist
the rubber boot slightly (1/2 turn) to break it loose
(Fig. 19). Grasp the boot (not the cable) and pull it
off with a steady, even force.
Install cables into the proper engine cylinder firing
order (Figs. 21 or 22).
When replacing the spark plug and coil cables,
route the cables correctly and secure in the proper
retainers. Failure to route the cables properly can
cause the radio to reproduce ignition noise. It could
also cause cross ignition of the plugs, or short circuit
the cables to ground.
Fig. 19 Cable Removal
Fig. 20 Setting Spark Plug GapÐTypical
8D - 24 IGNITION SYSTEMSJ