1994 JEEP CHEROKEE heating

ENGINE BLOCK HEATER
GENERAL INFORMATION
DESCRIPTION AND OPERATION
An optional engine block heater is available for all
models. The heater is equipped with a power cord.
The cord is attached to an engine compartment com-
ponent with tie-straps. The heater warms the engine
providing easier engine starting and faster warm-up
in low temperatures. The heater is mounted in a core
hole of the engine cylinder block (in place of a freeze
plug) with the heating element immersed in engine
coolant. Connect the power cord to a grounded 110-
120 volt AC electrical outlet with a grounded, three-
wire extension cord.
WARNING: DO NOT OPERATE ENGINE UNLESS
BLOCK HEATER CORD HAS BEEN DISCONNECTED
FROM POWER SOURCE AND SECURED IN PLACE.
BLOCK HEATER SPECIFICATIONS
²2.5L Engine: 115 Volts 400 Watts
²4.0L Engine: 120 Volts 600 Watts
REMOVAL
Refer to correct illustration (Figures 11, 12 or 13)
when servicing block heater.
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAINCOCK WITH THE SYSTEM HOT AND PRES-
SURIZED. SERIOUS BURNS FROM THE COOLANT
CAN OCCUR.
DO NOT WASTE reusable coolant. If solution is
clean, drain coolant into a clean container for reuse.
(1) Drain coolant from radiator and engine cylin-
der block.
(2) Unplug power cord from block heater.
(3) Loosen screw in center of block heater (Figs.
11, 12 or 13).
(4) Remove block heater from cylinder block.
INSTALLATION
(1) Thoroughly clean the engine core hole and the
block heater seat.
(2) Insert block heater assembly into core hole
with element loop pointingUp.
(3) Seat block heater flush against block face.
Tighten mounting screw to 3.6 Nzm (32 in. lbs.)
torque.
(4) Fill cooling system with coolant. Pressurize sys-
tem and inspect for leaks.
(5) Plug power cord into block heater. Route cord
away from moving parts, linkages and exhaust sys-
tem components. Secure cord in place with tie-straps.
Fig. 11 Heater and CordÐXJ with 2.5L Engine
Fig. 12 Heater and CordÐXJ with 4.0L Engine
Fig. 13 Heater and CordÐYJ Models
JCOOLING SYSTEM 7 - 37

plugs with scavenger deposits can be considered nor-
mal in condition and can be cleaned using standard
procedures.
CHIPPED ELECTRODE INSULATOR
A chipped electrode insulator usually results from
bending the center electrode while adjusting the
spark plug electrode gap. Under certain conditions,
severe detonation can also separate the insulator
from the center electrode (Fig. 27). Spark plugs with
this condition must be replaced.
PREIGNITION DAMAGE
Preignition damage is usually caused by excessive
combustion chamber temperature. The center elec-
trode dissolves first and the ground electrode dis-
solves somewhat latter (Fig. 28). Insulators appear
relatively deposit free. Determine if the spark plug
has the correct heat range rating for the engine. De-
termine if ignition timing is over advanced, or if
other operating conditions are causing engine over-
heating. (The heat range rating refers to the operat-
ing temperature of a particular type spark plug.
Spark plugs are designed to operate within specifictemperature ranges. This depends upon the thickness
and length of the center electrodes porcelain insula-
tor.)
SPARK PLUG OVERHEATING
Overheating is indicated by a white or gray center
electrode insulator that also appears blistered (Fig.
29). The increase in electrode gap will be consider-
ably in excess of 0.001 inch per 1000 miles of opera-
tion. This suggests that a plug with a cooler heat
range rating should be used. Over advanced ignition
timing, detonation and cooling system malfunctions
can also cause spark plug overheating.
SPARK PLUG SECONDARY CABLES
TESTING
Spark plug cables are sometimes referred to as sec-
ondary ignition cables or secondary wires. The cables
transfer electrical current from the distributor to in-
dividual spark plugs at each cylinder. The spark plug
cables are of nonmetallic construction and have a
built in resistance. The cables provide suppression of
radio frequency emissions from the ignition system.
Fig. 26 Scavenger Deposits
Fig. 27 Chipped Electrode Insulator
Fig. 28 Preignition Damage
Fig. 29 Spark Plug Overheating
JIGNITION SYSTEMS 8D - 17

REAR WINDOW DEFOGGER
CONTENTS
page page
GENERAL.............................. 1
XJ .................................... 4YJ .................................... 4
GENERAL
INDEX
page page
Diagnosis............................... 2
Rear Window Defogger Grid Repair........... 2Rear Window Defogger Grid Test............. 1
Switch Testing............................ 2
Using heating elements bonded to the rear window
glass, the rear defogger will clear condensation, frost
and light snow coverings from the rear window.
The horizontal grid lines and vertical bus bar lines,
printed and baked on inside surface of the rear win-
dow glass, comprise an electrical circuit. The electri-
cally conductive lines are composed of a silver-
ceramic material which when baked on glass
becomes bonded to the glass and is highly resistant
to abrasion.
The electrical current required to produce the heat
in the grid is supplied through a relay and driver op-
erated switch. When the switch is momentarily de-
pressed, the relay senses a voltage change. This
voltage change causes the relay to change state and
complete a circuit to energize the relay. Once the re-
lay energizes, the contacts close connecting the grid
to battery power.
On the XJ, the power circuit to the grid is pro-
tected by the 25 amp, #18 fuse in the fuse box.
Power for fuse #18 comes from the power distribu-
tion center, fuse #F10. Power for the relay is pro-
tected by the 20 amp, #8 fuse located in the fuse box.
On the YJ, the grid is protected by a 25 amp #6
fuse, located in the fuse box. Power for the relay is
protected by 15 amp #9 fuse, located in the fuse box.
To defog the rear window, momentarily depress the
rocker switch. A light on the rocker switch will illu-
minate indicating that the defogger is operating.
If the ignition switch is ON the first activation of
the defog/defrost feature will last for 10 minutes.
Succeeding activations will last for 5 minutes unless
the ignition switch is turned OFF; then it will recy-
cle back to 10 minutes for the first activation.To stop defogger operation, momentarily push the
switch a second time.
CAUTION: Use care when washing the inside of the
rear window to prevent damage to the defogger
heating elements. Use a soft cloth and a mild wash-
ing solution. Wiping motions should be parallel to
the heating elements. Also, keep all objects a safe
distance from the window to prevent damaging the
heating elements.
REAR WINDOW DEFOGGER GRID TEST
It is possible, that a break may exist or occur in an
individual grid line resulting in no current flow
through the line. When a grid has an open circuit,
the area of glass normally cleared by that grid re-
mains fogged or iced unless, and until it is cleared by
the adjacent grids.
With the engine running at idle, push the rear
window defogger switch to the ON position and re-
lease. The pilot lamp in the rocker switch should
light, indicating defogger operation.
Using a 12-volt DC voltmeter, contact the positive
lead to the feed side vertical bus element on the in-
side surface of the glass. Contact the negative lead to
the ground side bus element. Meter should read be-
tween 11 and 13 volts. Connect the negative lead of
the voltmeter to a good ground; the meter reading
should be constant.
Keep the negative lead connected to ground. Use
the positive lead and carefully contact each grid at
the approximate centerline of the window.
JREAR WINDOW DEFOGGER 8N - 1

ENGINE DIAGNOSIS
Engine diagnosis is helpful in determining the
causes of malfunctions not detected and remedied by
routine tune-ups.
These malfunctions may be classified as either per-
formance (e.g., engine idles rough and stalls) or me-
chanical (e.g., a strange noise).
Refer to the Service DiagnosisÐPerformance chart
and the Service DiagnosisÐMechanical chart for pos-
sible causes and corrections of malfunctions. Refer to
Group 14, Fuel System for the fuel system diagnosis.
Additional tests and diagnostic procedures may be
necessary for specific engine malfunctions that can
not be isolated with the Service Diagnosis charts. In-
formation concerning additional tests and diagnosis
is provided within the following diagnosis:
²Cylinder Compression Pressure Test.
²Cylinder Combustion Pressure Leakage Test.
²Engine Cylinder Head Gasket Failure Diagnosis.
²Intake Manifold Leakage Diagnosis.
INTAKE MANIFOLD LEAKAGE DIAGNOSIS
An intake manifold air leak is characterized by
lower than normal manifold vacuum. Also, one or
more cylinders may not be functioning.
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 THE FAN.
DO NOT WEAR LOOSE CLOTHING.
METHOD 1
(1) Start the engine.
(2) Open the acetylene valve of an oxyacetylene
torch. DO NOT ignite.
(3) Pass the torch tip over the exposed gasket area
(EDGE) between the manifold and the engine cylin-
der head.
(4) If the engine speed increases, the manifold has
an air leak.
METHOD 2
(1) Start the engine.
(2) Apply engine oil to the exposed gasket area
(EDGE) between the manifold and the engine cylin-
der head.
(3) If oil is forced into the manifold and if smoke is
visible from the exhaust tailpipe, the manifold has
an air leak.
CYLINDER COMPRESSION PRESSURE TEST
The results of a cylinder compression pressure test
can be utilized to diagnose several engine malfunc-
tions.
Ensure the battery is completely charged and the
engine starter motor is in good operating condition.Otherwise the indicated compression pressures may
not be valid for diagnosis purposes.
(1) Clean the spark plug recesses with compressed
air.
(2) Remove the spark plugs.
(3) Secure the throttle in the wide-open position.
(4) Disconnect the ignition coil.
(5) Insert a compression pressure gauge and rotate
the engine with the engine starter motor for three
revolutions.
(6) Record the compression pressure on the 3rd
revolution. Continue the test for the remaining cyl-
inders.
Refer to Engine Specifications for the correct en-
gine compression pressures.
ENGINE CYLINDER HEAD GASKET FAILURE
DIAGNOSIS
A leaking engine cylinder head gasket usually re-
sults in loss of power, loss of coolant and engine mis-
firing.
An engine cylinder head gasket leak can be located
between adjacent cylinders or between a cylinder and
the adjacent water jacket.
²An engine cylinder head gasket leaking between
adjacent cylinders is indicated by a loss of power
and/or engine misfire.
²An engine cylinder head gasket leaking between a
cylinder and an adjacent water jacket is indicated by
coolant foaming or overheating and loss of coolant.
CYLINDER-TO-CYLINDER LEAKAGE TEST
To determine if an engine cylinder head gasket is
leaking between adjacent cylinders; follow the proce-
dures outlined in Cylinder Compression Pressure
Test. An engine cylinder head gasket leaking be-
tween adjacent cylinders will result in approximately
a 50-70% reduction in compression pressure.
CYLINDER-TO-WATER JACKET LEAKAGE
TEST
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 THE FAN.
DO NOT WEAR LOOSE CLOTHING.
Remove the radiator cap.
Start the engine and allow it to warm up until the
engine thermostat opens.
If a large combustion/compression pressure leak ex-
ists, bubbles will be visible in the coolant.
If bubbles are not visible, install a radiator pres-
sure tester and pressurize the coolant system.
JENGINES 9 - 5

12.7 mm (1/2 inch) replace it. The correct timing
chain has 48 pins. A chain with more than 48 pins
will cause excessive slack.
INSTALLATION
Assemble the timing chain, crankshaft sprocket
and camshaft sprocket with the timing marks
aligned (Fig. 6).
(1) Apply Mopar Silicone Rubber Adhesive Sealant
to the keyway in the crankshaft and insert the key.
With the key in the keyway on the crankshaft, in-
stall the assembly on the crankshaft and camshaft.
(2) Install the camshaft sprocket retaining preload
bolt and washer (Fig. 7). Tighten the preload bolt to
108 Nzm (80 ft. lbs.) torque.
(3) To verify correct installation of the timing
chain, turn the crankshaft to position the camshaft
sprocket timing mark as shown in Fig. 8. Count the
number of chain pins between the timing marks of
both sprockets. There must be 15 pins.
(4) Install the crankshaft oil slinger.
(5) Replace the oil seal in the timing case cover.(6) Lubricate the tension spring, thrust pin and
pin bore in the preload bolt with Mopar Engine Oil
Supplement, or equivalent. Install the spring and
thrust pin in the preload bolt head (Fig. 6).
(7) Install the timing case cover and gasket.
(8) With the key installed in the crankshaft key-
way, install the vibration damper, washer and bolt.
Lubricate and tighten the bolt to 108 Nzm (80 ft. lbs.)
torque.
(9) Install the serpentine drive belt and tighten to
the specified tension (refer to Group 7, Cooling Sys-
tem for the proper procedure).
(10) Install the fan and hub (or Tempatrol fan) as-
sembly. Install the shroud.
(11) Connect negative cable to battery.CAMSHAFT
REMOVAL
WARNING: THE COOLANT IN A RECENTLY OPER-
ATED ENGINE IS HOT AND PRESSURIZED. RE-
LEASE THE PRESSURE BEFORE REMOVING THE
DRAIN COCK, CAP AND DRAIN PLUGS.
(1) Disconnect negative cable from battery.
(2) Drain the cooling system. DO NOT waste reus-
able coolant. If the solution is clean, drain it into a
clean container for reuse.
(3) Remove the radiator or radiator/condenser, if
equipped with A/C (refer to Group 7, Cooling System
for the proper procedure).
(4) Remove the air conditioner condenser and re-
ceiver/drier assembly as a charged unit, if equipped
(refer to Group 24, Heating and Air Conditioning).
Fig. 6 Crankshaft/Camshaft AlignmentÐTypical
Fig. 7 Camshaft Sprocket Preload Bolt
Fig. 8 Verify Sprocket/Chain InstallationÐTypical
J4.0L ENGINE 9 - 69

(5) Remove the distributor cap and mark the posi-
tion of the rotor.
(6) Remove the distributor and ignition wires.
(7) Remove the engine cylinder head cover.
(8) Remove the rocker arms, bridges and pivots.
(9) Remove the push rods.
(10) Remove the engine cylinder head and gasket.
(11) Remove the hydraulic valve tappets from the
engine cylinder head.
(12) Remove the vibration damper.
(13) Remove the timing case cover.
(14) Remove the timing chain and sprockets.
(15) Remove the front bumper and/or grille, as re-
quired.
(16) Remove the camshaft (Fig. 9).
INSPECTION
Inspect the cam lobes for wear.
Inspect the bearing journals for uneven wear pat-
tern or finish.
Inspect the bearings for wear.
Inspect the distributor drive gear for wear.
If the camshaft appears to have been rubbing
against the timing case cover, examine the oil pres-
sure relief holes in the rear cam journal. The oil
pressure relief holes must be free of debris.
INSTALLATION
(1) Lubricate the camshaft with Mopar Engine Oil
Supplement, or equivalent.
(2) Carefully install the camshaft to prevent dam-
age to the camshaft bearings (Fig. 9).
(3) Install the timing chain, crankshaft sprocket
and camshaft sprocket with the timing marks
aligned.
(4) Install the camshaft sprocket retaining preload
bolt. Tighten the bolt to 108 Nzm (80 ft. lbs.) torque.
(5) Lubricate the tension spring, the thrust pin
and the pin bore in the preload bolt with Mopar En-
gine Oil Supplement, or equivalent. Install the
spring and thrust pin in the preload bolt head.(6) Install the timing case cover with a replace-
ment oil seal (Fig. 10). Refer to Timing Case Cover
Installation.
(7) Install the vibration damper (Fig. 10).
(8) Install the hydraulic valve tappets.
(9) Install the engine cylinder head.
(10) Install the push rods.
(11) Install the rocker arms and pivot and bridge
assemblies. Tighten each of the capscrews for each
bridge alternately, one turn at a time, to avoid dam-
aging the bridge.
(12) Install the engine cylinder head cover.
(13) Install the serpentine drive belt and tighten to
the specified tension (refer to Group 7, Cooling Sys-
tem for the proper procedure).
(14) Rotate the crankshaft until the No.1 piston is
at the TDC position on the compression stroke.
(15) Install the distributor, cap and ignition wires.
Install the distributor so that the rotor is aligned
with the mark made during removal. The rotor
should be aligned with the No.1 cylinder spark plug
terminal on the cap when the distributor housing is
fully seated on the cylinder block.
During installation, lubricate the hydraulic
valve tappets and all valve components with Mo-
par Engine Oil Supplement, or equivalent. The
Mopar Engine Oil Supplement, or equivalent
must remain with the engine oil for at least 1 609
km (1,000 miles). The oil supplement need not be
drained until the next scheduled oil change.
(16) Install the A/C condenser and receiver/drier
assembly, if equipped (refer to Group 24, Heating
and Air Conditioning).
CAUTION: Both service valves must be opened be-
fore the air conditioning system is operated.
(17) Install the radiator, connect the hoses and fill
the cooling system to the specified level (refer to
Group 7, Cooling System for the proper procedure).
Fig. 9 Camshaft
Fig. 10 Timing Case Cover Components
9 - 70 4.0L ENGINEJ

EXHAUST SYSTEM AND INTAKE MANIFOLD
CONTENTS
page page
EXHAUST SYSTEM....................... 1
EXHAUST SYSTEM DIAGNOSIS............ 2SERVICE PROCEDURES................... 3
TORQUE SPECIFICATIONS................ 10
EXHAUST SYSTEM
GENERAL INFORMATION
The basic exhaust system consists of an engine ex-
haust manifold, exhaust pipe with oxygen sensor,
catalytic converter, exhaust heat shield(s), muffler
and exhaust tailpipe (Fig. 1).
The exhaust system uses a single muffler with a
single monolithic-type catalytic converter.
The 4.0L engines use a seal between the engine ex-
haust manifold and exhaust pipe to assure a tight
seal and strain free connections.
The exhaust system must be properly aligned to
prevent stress, leakage and body contact. If the sys-tem contacts any body panel, it may amplify objec-
tionable noises originating from the engine or body.
When inspecting an exhaust system, critically in-
spect for cracked or loose joints, stripped screw or
bolt threads, corrosion damage and worn, cracked or
broken hangers. Replace all components that are
badly corroded or damaged. DO NOT attempt to re-
pair.
When replacement is required, use original equip-
ment parts (or their equivalent). This will assure
proper alignment and provide acceptable exhaust
noise levels.
CAUTION: Avoid application of rust prevention
compounds or undercoating materials to exhaust
system floor pan exhaust heat shields. Light overs-
pray near the edges is permitted. Application of
coating will result in excessive floor pan tempera-
tures and objectionable fumes.
CATALYTIC CONVERTER
The stainless steel catalytic converter body is de-
signed to last the life of the vehicle. Excessive heat
can result in bulging or other distortion, but exces-
sive heat will not be the fault of the converter. If un-
burned fuel enters the converter, overheating may
occur. If a converter is heat-damaged, correct the
cause of the damage at the same time the converter
is replaced. Also, inspect all other components of the
exhaust system for heat damage.
Unleaded gasoline must be used to avoid contami-
nating the catalyst core.
EXHAUST HEAT SHIELDS
Exhaust heat shields are needed to protect both the
vehicle and the environment from the high tempera-
tures developed by the catalytic converter. The cata-
lytic converter releases additional heat into the
exhaust system. Under severe operating conditions,
the temperature increases in the area of the con-
Fig. 1 Typical Exhaust System
JEXHAUST SYSTEM AND INTAKE MANIFOLD 11 - 1

CAUTION: Ensure that the accessory drive belt is
routed correctly. Failure to do so can cause the wa-
ter pump to turn in the opposite direction resulting
in engine overheating. Refer to Group 7, Cooling
System for the proper procedure.
(10) Tension the accessory drive belt. Refer to
Group 7, Cooling System for the proper procedure.
(11) Connect the air inlet hose to the throttle body
and the air cleaner.
(12) Connect the battery negative cable.
(13) Start the engine and check for leaks.
INTAKE MANIFOLDÐ4.0L ENGINE
The intake and engine exhaust manifolds on the
4.0L engine must be removed and installed together.
The two manifolds use a common gasket at the cyl-
inder head.
REMOVAL
(1) Disconnect the battery negative cable.
(2) Remove air cleaner inlet hose from throttle
plate assembly.
(3) Remove the air cleaner assembly.
(4) Remove the throttle cable, cruise control cable (if
equipped) and the transmission line pressure cable.
(5) Disconnect all electrical connectors on the in-
take manifold.
(6) Disconnect and remove the fuel supply and re-
turn lines from the fuel rail assembly (refer to Group
14, Fuel System).
(7) Loosen the accessory drive belt (refer to Group
7, Cooling System). Loosen the tensioner.
(8) Remove the power steering pump and bracket
from the intake manifold and set aside.
(9) Remove the fuel rail and injectors (refer to
Group 14, Fuel System).
(10) Raise the vehicle.
(11) Disconnect the exhaust pipe from the engine
exhaust manifold. Discard the seal.
(12) Lower the vehicle.
(13) Remove the intake manifold and engine ex-
haust manifold.
CLEANING
Clean the mating surfaces of the cylinder head and
the manifold if the original manifold is to be installed.
If the manifold is being replaced, ensure all the fit-
ting, etc. are transferred to the replacement manifold.
INSTALLATION
(1) Install a new exhaust/intake manifold gasket
over the alignment dowels on the cylinder head.
(2) Position the engine exhaust manifold to the
cylinder head. Install fastener No.3 and finger
tighten at this time (Fig. 13).
(3) Install intake manifold on the cylinder head
dowels.(4) Install washers and fasteners Nos.1, 2, 4, 5, 8,
9, 10 and 11 (Fig. 13).
(5) Install washers and fasteners Nos.6 and 7 (Fig. 13).
(6) Tighten the fasteners in sequence and to the
specified torque (Fig. 13).
²Fasteners Nos.1 through 5ÐTighten to 33 Nzm (24
ft. lbs.) torque.
²Fasteners Nos.6 and 7ÐTighten to 31 Nzm (23 ft.
lbs.) torque.
²Fasteners Nos.8 through 11ÐTighten to 33 Nzm
(24 ft. lbs.) torque.
(7) Install the fuel rail and injectors.
(8) Install the power steering pump and bracket to the
intake manifold. Tighten the belt to specification. Refer
to Group 7, Cooling System for the proper procedures.
(9) Install the fuel supply and return lines to the
fuel rail assembly.Before connecting the fuel
lines to the fuel rail replace the O-rings in the
quick-connect fuel line couplings.Refer to Group
14, Fuel System for the proper procedure.
(10) Connect all electrical connections on the in-
take manifold.
(11) Connect the vacuum connector on the intake
manifold and install it in the bracket.
(12) Install throttle cable, cruise control cable (if
equipped).
(13) Install the transmission line pressure cable (if
equipped). Refer to Group 21, Transmission for the
adjustment procedures.
(14) Install air cleaner assembly.
(15) Connect air inlet hose to the throttle plate as-
sembly.
(16) Raise the vehicle on a side mounted hoist.
(17) Using a new seal, connect the exhaust pipe to
the engine exhaust manifold. Tighten the bolts to 31
Nzm (23 ft. lbs.) torque.
(18) Lower the vehicle.
(19) Connect the battery negative cable.
(20) Start the engine and check for leaks.
Fig. 13 Intake/Engine Exhaust Manifold Installation
(4.0L Engine)
JEXHAUST SYSTEM AND INTAKE MANIFOLD 11 - 9