2002 JEEP GRAND CHEROKEE Bus

²6th & 7th DigitsÐThe day of engine build (01 -
31).(1)FOR EXAMPLE:Code * 801MX12 * identifies
a 4.0 Liter (242 CID) engine with a multi-point fuel
injection system, 8.7:1 compression ratio and built on
January 12, 1998.
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - ENGINE
DIAGNOSIS - INTRODUCTION
Engine diagnosis is helpful in determining the
causes of malfunctions not detected and remedied by
routine maintenance.
These malfunctions may be classified as either
mechanical (e.g., a strange noise), or performance
(e.g., engine idles rough and stalls).
(Refer to 9 - ENGINE - DIAGNOSIS AND TEST-
ING - Preformance) or (Refer to 9 - ENGINE - DIAG-
NOSIS AND TESTING - Mechanical). Refer to 14 -
FUEL SYSTEM for 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.
Information concerning additional tests and diagno-
sis is provided within the following:
²Cylinder Compression Pressure Test (Refer to 9 -
ENGINE - DIAGNOSIS AND TESTING)
²Cylinder Combustion Pressure Leakage Test
(Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)
²Cylinder Head Gasket Failure Diagnosis (Refer
to 9 - ENGINE/CYLINDER HEAD - DIAGNOSIS
AND TESTING)
²Intake Manifold Leakage Diagnosis (Refer to 9 -
ENGINE/MANIFOLDS/INTAKE MANIFOLD -
DIAGNOSIS AND TESTING)
²Lash Adjuster (Tappet) Noise Diagnosis (Refer to
9 - ENGINE/ENGINE BLOCK/HYDRAULIC LIFT-
ERS (CAM IN BLOCK) - DIAGNOSIS AND TEST-
ING)
²Engine Oil Leak Inspection (Refer to 9 -
ENGINE/LUBRICATION - DIAGNOSIS AND TEST-
ING)
Fig. 1 Engine Firing Order
Fig. 2 Build Date Code Location
1 - YEAR
2 - MONTH
3-DAY
WJENGINE - 4.0L 9 - 3
ENGINE - 4.0L (Continued)

DIAGNOSIS AND TESTINGÐCYLINDER
COMPRESSION PRESSURE
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 (Refer to 8 - ELEC-
TRICAL/IGNITION CONTROL/SPARK PLUG -
REMOVAL).
(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 third
revolution. Continue the test for the remaining cylin-
ders.
(Refer to 9 - ENGINE - SPECIFICATIONS) for the
correct engine compression pressures.
DIAGNOSIS AND TESTING - CYLINDER
COMBUSTION PRESSURE LEAKAGE
The combustion pressure leakage test provides an
accurate means for determining engine condition.
Combustion pressure leakage testing will detect:
²Exhaust and intake valve leaks (improper seat-
ing)
²Leaks between adjacent cylinders or into water
jacket²Any causes for combustion/compression pressure
loss
WARNING: DO NOT REMOVE THE RADIATOR CAP
WITH THE SYSTEM HOT AND UNDER PRESSURE.
SERIOUS BURNS FROM HOT COOLANT CAN
OCCUR.
Check the coolant level and fill as required. DO
NOT install the radiator cap.
Start and operate the engine until it attains nor-
mal operating temperature, then turn OFF the
engine.
Remove the spark plugs.
Remove the oil filler cap.
Remove the air cleaner.
Calibrate the tester according to the manufactur-
er's instructions. The shop air source for testing
should maintain 483 kPa (70 psi) minimum, 1,379
kPa (200 psi) maximum and 552 kPa (80 psi) recom-
mended.
Perform the test procedure on each cylinder accord-
ing to the tester manufacturer's instructions. While
testing, listen for pressurized air escaping through
the throttle body, tailpipe or oil filler cap opening.
Check for bubbles in the radiator coolant.
All gauge pressure indications should be equal,
with no more than 25% leakage.
FOR EXAMPLE:At 552 kPa (80 psi) input pres-
sure, a minimum of 414 kPa (60 psi) should be main-
tained in the cylinder CYLINDER COMBUSTION
PRESSURE LEAKAGE DIAGNOSIS CHART .
CYLINDER COMBUSTION PRESSURE LEAKAGE DIAGNOSIS CHART
CONDITION POSSIBLE CAUSE CORRECTION
AIR ESCAPES THROUGH
THROTTLE BODYIntake valve bent, burnt, or not
seated properlyInspect valve and valve seat.
Reface or replace, as necessary
AIR ESCAPES THROUGH
TAILPIPEExhaust valve bent, burnt, or not
seated properlyInspect valve and valve seat.
Reface or replace, as necessary
AIR ESCAPES THROUGH
RADIATORHead gasket leaking or cracked
cylinder head or blockRemove cylinder head and inspect.
Replace defective part
MORE THAN 50% LEAKAGE
FROM ADJACENT CYLINDERSHead gasket leaking or crack in
cylinder head or block between
adjacent cylindersRemove cylinder head and inspect.
Replace gasket, head, or block as
necessary
MORE THAN 25% LEAKAGE AND
AIR ESCAPES THROUGH OIL
FILLER CAP OPENING ONLYStuck or broken piston rings;
cracked piston; worn rings and/or
cylinder wallInspect for broken rings or piston.
Measure ring gap and cylinder
diameter, taper and out-of-round.
Replace defective part as necessary
9 - 8 ENGINE - 4.0LWJ
ENGINE - 4.0L (Continued)

WARNING: USE EXTREME CAUTION WHEN THE
ENGINE IS OPERATING. DO NOT STAND IN A
DIRECT LINE WITH THE FAN. DO NOT PUT YOUR
HANDS NEAR THE PULLEYS, BELTS OR FAN. DO
NOT WEAR LOOSE CLOTHING.
(48) Start the engine, inspect for leaks and correct
the fluid levels, as necessary.
SPECIFICATIONS
ENGINE - 4.0L
DESCRIPTION SPECIFICATION
Engine Type In-line 6 Cylinder
Bore and Stroke 98.4 x 86.69 mm
(3.88 x 3.413 in.)
Displacement 4.0L (242 cu. in.)
Compression Ratio 8.8:1
Firing Order 1±5±3±6±2±4
Lubrication Pressure Feed±Full Flow
Filtration
Cooling System Liquid Cooled±Forced
Circulation
Cylinder Block Cast Iron
Crankshaft Cast Nodular Iron
Cylinder Head Cast Iron
Camshaft Cast Iron
Pistons Aluminum Alloy
Combustion Chamber Dual-Quench
Connecting Rods Cast Malleable Iron
CAMSHAFT
Hydraulic Tappet
ClearanceZero Lash
Bearing Clearance 0.025 to 0.076 mm
(0.001 to 0.003 in.)
DESCRIPTION SPECIFICATION
Bearing Journal Diameter
No. 1 51.54 to 51.56 mm
(2.029 to 2.030 in.)
No. 2 51.28 to 51.31 mm
(2.019 to 2.020 in.)
No. 3 51.03 to 51.05 mm
(2.009 to 2.010 in.)
No. 4 50.78 to 50.80 mm
(1.999 to 2.000 in.)
Base Circle Runout
(MAX)0.03 mm
(0.001 in.)
Valve Lift
Intake 10.350 mm (0.4075 in.)
Exhaust 10.528 mm (0.4145 in.)
Valve Timing
Intake
Opens 12.4É BTDC
Closes 60.9É ABDC
Exhaust
Opens 49.8 BBDC
Closes 29.2É ATDC
Valve Overlap 41.6É
Intake Duration 253.3É
Exhaust Duration 259.É
CRANKSHAFT
End Play 0.038 to 0.165 mm
(0.0015 to 0.0065 in.)
Main Bearing Journal
Diameter
No. 1-6 63.489 to 63.502 mm
(2.4996 to 2.5001 in.)
No. 7 63.449 to 63.487 mm
(2.4980 to 2.4995 in.)
9 - 14 ENGINE - 4.0LWJ
ENGINE - 4.0L (Continued)

DESCRIPTION SPECIFICATION
Main Bearing Journal
Width
No. 1 27.58 to 27.89 mm
(1.086 to 1.098 in.)
No. 3 32.28 to 32.33 mm
(1.271 to 1.273 in.)
No. 2-4-5-6-7 30.02 to 30.18 mm
(1.182 to 1.188 in.)
Main Bearing Clearance 0.03 to 0.06 mm
(0.001 to 0.0025 in.)
Preferred 0.051 mm (0.002 in.)
Connecting Rod Journal
Diameter 53.17 to 53.23 mm
(2.0934 to 2.0955 in.)
Connecting Rod Journal
Width27.18 to 27.33 mm
(1.070 to 1.076 in.)
Out-of-Round (MAX) 0.013 mm (0.0005 in.)
Taper (MAX) 0.013 mm (0.0005 in.)
CYLINDER BLOCK
Deck Height 240.03 to 240.18 mm
(9.450 to 9.456 in.)
Deck Clearance (Below
Block)0.546 mm (0.0215 in.)
Cylinder Bore Diameter
Standard 98.45 to 98.48 mm
(3.8759 to 3.8775 in.)
Taper 0.025 mm (0.001 in.)
Out-ofRound 0.025 mm (0.001 in.)
Tappet Bore Diameter 23.000 to 23.025 mm
(0.9055 to 0.9065 in.)
Flatness 0.03 mm per 25 mm
(0.001 in. per 1 in.)
0.05 mm per 152 mm
(0.002 in. per 6 in.)
Flatness Max. 0.20 mm max. for total
lengthDESCRIPTION SPECIFICATION
(0.008 in. max. for total
length)
Main Bearing Bore
Diameter68.3514 to 68.3768 mm
(2.691 to 2.692 in.)
CONNECTING ROD
Total Weight (Less
Bearing)663 to 671 grams
(23.39 to 23.67 oz.)
Length (Center-to-Center) 155.52 to 155.62 mm
(6.123 to 6.127 in.)
Piston Pin Bore Diameter 23.59 to 23.62 mm
(0.9288 to 0.9298 in.)
Bore (Less Bearings) 56.08 to 56.09 mm
(2.2080 to 2.2085 in.)
Bearing Clearance 0.025 to 0.076 mm
(0.001 to 0.003 in.)
Preferred 0.044 to 0.050 mm
(0.0015 to 0.0020 in.)
Side Clearance 0.25 to 0.48 mm
(0.010 to 0.019 in.)
Twist (Max.) 0.002 mm per mm
(0.002 in. per inch)
Bend (Max.) 0.002 mm per mm
(0.002 in. per inch.)
CYLINDER COMPRESSION PRESSURE
Pressure Range 827 to 1,034 kPa
(120 to 150 psi)
Max. Variation Between
Cylinders 206 kPa (30 psi)
CYLINDER HEAD
Combustion Chamber 55.22 to 58.22 cc
(3.37 to 3.55 cu. in.)
Valve Guide I.D.
(Integral)7.95 to 7.97 mm
(0.313 to 0.314 in.)
WJENGINE - 4.0L 9 - 15
ENGINE - 4.0L (Continued)

(2) Lift cover up and position to the side.
(3) Remove air cleaner element.
INSTALLATION - 4.0L
(1) Clean inside of air cleaner housing before
installing new element.
(2) Install air cleaner element into housing.
(3) Latch clips and clamp cover down to secure. Be
sure air cleaner cover is properly seated to air
cleaner housing.
AIR CLEANER HOUSING
REMOVAL - 4.0L
(1) Disconnect air cleaner cover-to-air duct clamp
(Fig. 6).
(2) Disconnect air duct at housing.
(3)Each of the 3 air cleaner housing mount-
ing bolts is attached with 2 nuts (an upper nut
and lower nut). DO NOT REMOVE BOLTS. To
prevent stripping bolts, only remove lower
nuts. The lower housing nuts are located under
left front inner fender (Fig. 6).
(a) To gain access to lower nuts, raise vehicle.
(b) Remove clips retaining rubber inner fender
shield.
(c) Pry back shield enough to gain access to
lower nuts.
(d) Remove 3 nuts.
(e) Remove air cleaner assembly from vehicle.
(4) If resonator is to be removed, disconnect
breather tube at resonator, disconnect air duct clamp
at resonator (Fig. 6)and remove 1 resonator mount-
ing bolt. Remove resonator from throttle body by
loosening clamp (Fig. 7).
INSTALLATION - 4.0L
(1) Position air cleaner assembly to body and
install 3 nuts. Tighten nuts to 10 N´m (93 in. lbs.)
torque.To prevent excessive vibration transmit-
ted through housing, the nuts must be properly
torqued. Do not overtighten nuts.
(2) If resonator was removed: Install resonator and
bolts. Tighten bolts to 4 N´m (35 in. lbs.) torque.
Tighten clamp at throttle body to 4 N´m (35 in. lbs.)
torque.
(3) Position fender liner and install clips.
(4) Connect air duct at housing (Fig. 6).
(5) Tighten air duct clamp.
CYLINDER HEAD
DESCRIPTION
The cylinder head is made of cast iron containing
twelve valves made of chrome plated heat resistant
steel, valve stem seals, springs, retainers and keep-
ers. The cylinder head and valve seats can be resur-
faced for service purposes.
The valve guides are integral to the cylinder head,
They are not replaceable. However, they are service-
able.
The cylinder head uses dual quench-type design
combustion chambers which cause turbulence in the
cylinders allowing faster burning of the air/fuel mix-
ture, resulting in better fuel economy (Fig. 8).
REMOVAL
NOTE: This procedure can be done with the engine
in or out of the vehicle.
(1) Disconnect the battery negative cable.
WARNING: DO NOT REMOVE THE CYLINDER
BLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR
DRAIN COCK WITH THE SYSTEM HOT AND PRES-
SURIZED BECAUSE SERIOUS BURNS FROM THE
COOLANT CAN OCCUR.
Fig. 7 RESONATOR CLAMP - 4.0L
1 - RESONATOR
2 - AIR DUCT
3 - CLAMP
WJENGINE - 4.0L 9 - 19
AIR CLEANER ELEMENT (Continued)

CLEANING
Thoroughly clean the engine cylinder head and cyl-
inder block mating surfaces. Clean the intake and
engine exhaust manifold and engine cylinder head
mating surfaces. Remove all gasket material and car-
bon.
Check to ensure that no coolant or foreign material
has fallen into the tappet bore area.
Remove the carbon deposits from the combustion
chambers and top of the pistons.
INSPECTION
Use a straightedge and feeler gauge to check the
flatness of the engine cylinder head and block mating
surfaces.
INSTALLATION
NOTE: This procedure can be done with the engine
in or out of the vehicle.
The engine cylinder head gasket is a composition
gasket. The gasket is to be installed DRY.DO NOT
use a gasket sealing compound on the gasket.
If the engine cylinder head is to be replaced and
the original valves used, measure the valve stem
diameter. Only standard size valves can be used with
a service replacement engine cylinder head unless
the replacement head valve stem guide bores are
reamed to accommodate oversize valve stems.
Remove all carbon buildup and reface the valves.
(1) Remove the shop towels from the cylinder
bores. Coat the bores with clean engine oil.
(2) Position the engine cylinder head gasket (with
the numbers facing up) using the alignment dowels
in the cylinder block, to position the gasket.
CAUTION: Engine cylinder head bolts should be
reused only once. Replace the head bolts if they
were used before or if they have a paint dab on the
top of the bolt.
(3) With bolt No.14 held in place (tape around
bolt), install the engine cylinder head over the same
dowels used to locate the gasket. Remove the tape
from bolt No.14.
(4) Coat the threads of stud bolt No.11 with Loc-
tite 592 sealant, or equivalent.
(5) Tighten the engine cylinder head bolts in
sequence according to the following procedure (Fig.
10).
CAUTION: During the final tightening sequence,
bolt No.11 will be tightened to a lower torque than
the rest of the bolts. DO NOT overtighten bolt
No.11.(a) Tighten all bolts in sequence (1 through 14)
to 30 N´m (22 ft. lbs.) torque.
(b) Tighten all bolts in sequence (1 through 14)
to 61 N´m (45 ft. lbs.) torque.
(c) Check all bolts to verify they are set to 61
N´m (45 ft. lbs.) torque.
(d) Tighten bolts in sequence:
²Bolts 1 through 10 to 149 N´m (110 ft. lbs.)
torque.
²Bolt 11 to 135 N´m (100 ft. lbs.) torque.
²Bolts 12 through 14 to 149 N´m (110 ft. lbs.)
torque.
CYLINDER HEAD BOLTS
POSITION DESCRIPTION
1,4,5,12,13 1/2 in.-13 BOLT
8,9 1/2 in.-13 BOLT WITH DOWEL
POINT
2,3,6,7,10,11,14 1/2 in.-13 WITH 7/16 in.-14 STUD
END
All bolts are 12 point drives for rocker cover clearance
(e) Check all bolts in sequence to verify the cor-
rect torque.
(f) If not already done, clean and mark each bolt
with a dab of paint after tightening. Should you
encounter bolts which were painted in an earlier
service operation, replace them.
(6) Install the spark plugs (Refer to 8 - ELECTRI-
CAL/IGNITION CONTROL/SPARK PLUG - INSTAL-
LATION).
(7) Connect the temperature sending unit wire
connector.
(8) Install the ignition coil rail (Refer to 8 - ELEC-
TRICAL/IGNITION CONTROL/COIL RAIL -
INSTALLATION).
(9) Install the intake and exhaust manifolds (Refer
to 9 - ENGINE/MANIFOLDS/INTAKE MANIFOLD -
INSTALLATION).
(10) Install the fuel line.
(11) Attach the power steering pump and bracket.
Fig. 10 Engine Cylinder Head Bolt Tightening
Sequence
WJENGINE - 4.0L 9 - 21
CYLINDER HEAD (Continued)

CLEANING
Remove any original sealer from the cover sealing
surface of the engine cylinder head and clean the
surface using a fabric cleaner.
Remove all residue from the sealing surface using
a clean, dry cloth.
INSPECTION
Inspect the engine cylinder head cover for cracks.
Replace the cover, if cracked.
The original dark grey gasket material should
NOT be removed. If sections of the gasket material
are missing or are compressed, replace the engine
cylinder head cover. However, sections with minor
damage such as small cracks, cuts or chips may be
repaired with a hand held applicator. The new mate-
rial must be smoothed over to maintain gasket
height. Allow the gasket material to cure prior to
engine cylinder head cover installation.
INSTALLATION
The cylinder head cover is isolated from the cylin-
der head via grommets and a reusable molded rubber
gasket. The grommet and limiter are retained in the
cylinder head cover.
(1) If a replacement cover is installed, transfer the
CCV valve grommet and oil filler cap from the origi-
nal cover to the replacement cover.
(2) Install cylinder head cover and gasket (Fig. 13).
Tighten the mounting bolts to 10 N´m (85 in. lbs.)
torque.
(3) Connect the CCV hoses.(4) Install control cables and bracket on intake
manifold and tighten bolts to 8.7 N´m (77 in. lbs.)
torque.
(5) Connect control cables to throttle body linkage.
(6) Snap control cables into cylinder head cover
clip.
(7) Connect negative cable to battery.
INTAKE/EXHAUST VALVES &
SEATS
DESCRIPTION
The valves are made of heat resistant steel and
have chrome plated stems to prevent scuffing. All
valves use three bead locks to promote valve rotation
(Fig. 14).
STANDARD PROCEDURE - VALVE SERVICE
VALVE REFACING
Clean all carbon deposits from the combustion
chambers, valve ports, valve stems, valve stem
guides and head.
(1) Use a valve refacing machine to reface the
intake and exhaust valves to the specified angle.
(2) After refacing, a margin of at least 0.787 mm
(0.031 inch) must remain (Fig. 15). If the margin is
less than 0.787 mm (0.031 inch), the valve must be
replaced.
VALVE SEAT REFACING
Clean all carbon deposits from the combustion
chambers, valve ports, valve stems, valve stem
guides and head.
(1) Install a pilot of the correct size in the valve
guide bore. Reface the valve seat to the specified
angle with a good dressing stone. Remove only
enough metal to provide a smooth finish.
(2) Use tapered stones to obtain the specified seat
width when required.
Fig. 12 Engine Cylinder Head Cover
1 - TRANS CONTROL CABLE
2 - ACCELERATOR CABLE
3 - CONTROL CABLE BRACKET
4 - CYLINDER HEAD COVER
Fig. 13 Cylinder Head Cover Gasket Locator Pins at
#8
WJENGINE - 4.0L 9 - 23
CYLINDER HEAD COVER(S) (Continued)

VALVE SPRINGS
DESCRIPTION
The valve springs (Fig. 25) are made of high
strength silicon chrome spring steel. The springs are
common for both intake and exhaust valves.
STANDARD PROCEDURE - VALVE SPRING
TENSION TEST
Clean all carbon deposits from the combustion
chambers, valve ports, valve stems, valve stem
guides and head.
Use a universal Valve Spring Tester and a torque
wrench to test each valve spring for the specified ten-
sion value (Fig. 26).
Replace valve springs that are not within specifica-
tions.
REMOVAL
NOTE: This procedure can be done with the engine
cylinder head installed on the block.
Inspect the valve stems, especially the grooves. An
Arkansas smooth stone should be used to remove
nicks and high spots.Each valve spring is held in place by a retainer
and a set of conical valve locks. The locks can be
removed only by compressing the valve spring.
(1) Remove the engine cylinder head cover (Refer
to 9 - ENGINE/CYLINDER HEAD/CYLINDER
HEAD COVER(S) - REMOVAL).
Fig. 24 Valve
1 - VALVE LOCKS (3±BEAD)
2 - RETAINER
3 - VALVE STEM OIL SEAL
4 - INTAKE VALVE
5 - EXHAUST VALVE
6 - VALVE SPRING
Fig. 25 VALVE AND KEEPER CONFIGURATION 4.0L
1 - VALVE LOCKS (3±BEAD)
2 - RETAINER
3 - VALVE STEM OIL SEAL
4 - INTAKE VALVE
5 - EXHAUST VALVE
6 - VALVE SPRING
Fig. 26 Valve Spring Tester
1 - TORQUE WRENCH
2 - VALVE SPRING TESTER
9 - 28 ENGINE - 4.0LWJ
VALVE STEM SEALS (Continued)