light JEEP CHEROKEE 1988 Service Manual PDF

NOTE: Always refer to appropriate engine overhaul article in the
ENGINES section for complete overhaul procedures and
specifications for the vehicle being repaired.
REMOVAL
Remove intake and exhaust manifolds and valve cover. Cylinder
head and camshaft carrier bolts (if equipped), should be removed only
when the engine is cold. On many aluminum cylinder heads, removal
while hot will cause cylinder head warpage. Mark rocker arm or
overhead cam components for location.
Remove rocker arm components or overhead cam components.
Components must be installed in original location. Individual design
rocker arms may utilize shafts, ball-type pedestal mounts or no rocker
arms. For all design types, wire components together and identify
according to the corresponding valve. Remove cylinder head bolts.
Note length and location. Some applications require cylinder head
bolts be removed in proper sequence to prevent cylinder head damage.
See Fig. 1 . Remove cylinder head.
Fig. 1: Typical Cylinder Head Tightening or Loosening Sequence
This Graphic For General Information Only
INSTALLATION
Ensure all surfaces and head bolts are clean. Check that head
bolt holes of cylinder block are clean and dry to prevent block damage
when bolts are tightened. Clean threads with tap to ensure accurate
bolt torque.
Install head gasket on cylinder block. Some manufacturer's
may recommend sealant be applied to head gasket prior to installation.
Note that all holes are aligned. Some gasket applications may be
marked so certain area faces upward. Install cylinder head using care
not to damage head gasket. Ensure cylinder head is fully seated on
cylinder block.
Some applications require head bolts be coated with sealant
prior to installation. This is done if head bolts are exposed to water
passages. Some applications require head bolts be coated with light
coat of engine oil.

during manufacture, some new type valves cannot be reground.
Resurface valve on proper angle specification using valve
grinding machine. Follow manufacturer's instructions for valve
grinding machine. Specifications may indicate a different valve face
angle than seat angle.
Measure valve margin after grinding. Replace valve if not
within specification. Valve stem tip can be refinished using valve
grinding machine.
Valve Lapping
During valve lapping of recent designed valves, be sure to
follow manufacturers recommendations. Surface hardening and materials
used with some valves do not permit lapping. Lapping process will
remove excessive amounts of the hardened surface.
Valve lapping is done to ensure adequate sealing between
valve face and seat. Use either a hand drill or lapping stick with
suction cup attached.
Moisten and attach suction cup to valve. Lubricate valve stem
and guide. Apply a thin coat of fine valve grinding compound between
valve and seat. Rotate lapping tool between the palms or with hand
drill.
Lift valve upward off the seat and change position often.
This is done to prevent grooving of valve seat. Lap valve until a
smooth polished seat is obtained. Thoroughly clean grinding compound
from components. Valve to valve seat concentricity should be checked.
See VALVE SEAT CONCENTRICITY.
CAUTION: Valve guides must be in good condition and free of carbon
deposits prior to valve seat grinding. Some engines contain
an induction hardened valve seat. Excessive material removal
will damage valve seats.
Valve Seat Grinding
Select coarse stone of correct size and angle for seat to be
ground. Ensure stone is true and has a smooth surface. Select correct
size pilot for valve guide dimension. Install pilot in valve guide.
Lightly lubricate pilot shaft. Install stone on pilot. Move stone off
and on the seat approximately 2 times per second during grinding
operation.
Select a fine stone to finish grinding operation. Grinding
stones with 30 and 60 degree angles are used to center and narrow the
valve seat as required. See Fig. 10.
Fig. 10: Adjusting Valve Seat Width - Typical
This Graphic For General Information Only
Valve Seat Replacement
Replacement of valve seat inserts is done by cutting out

the old insert and machining an oversize insert bore. Replacement
oversize insert is usually chilled and the cylinder head is sometimes
warmed. Valve seat is pressed into the head. This operation requires
specialized machine shop equipment.
Valve Seat Concentricity
Using dial gauge, install gauge pilot in valve guide.
Position gauge arm on the valve seat. Adjust dial indicator to zero.
Rotate arm 360 degrees and note reading. Runout should not exceed
specification.
To check valve-to-valve seat concentricity, coat valve face
lightly with Prussian Blue dye. Install valve and rotate it on valve
seat. If pattern is even and entire seat is coated at valve contact
point, valve is concentric with the seat.
REASSEMBLY
Valve Stem Installed Height
Valve stem installed height must be checked when new valves
are installed or when valves or valve seats have been ground. Install
valve in valve guide. Measure distance from tip of valve stem to
spring seat. See Fig. 11. Distance must be within specifications.
Fig. 11: Measuring Valve Stem Installed Height - Typical
This Graphic For General Information Only
Remove valve and grind valve stem tip if height exceeds
specification. Valve tips are surface hardened. DO NOT remove more

over connecting rod bolts. Install piston and connecting rod assembly.
Ensure piston notch, arrow or "FRONT" mark is toward front of engine.
See Fig. 17 .
Fig. 17: Installing Piston & Connecting Rod Assembly - Typical
This Graphic For General Information Only
Carefully tap piston into cylinder until rod bearing is
seated on crankshaft journal. Remove protectors. Install rod cap and
bearing. Lightly tighten connecting rod bolts. Repeat procedure for
remaining cylinders. Check bearing clearance. See
MAIN & CONNECTING ROD BEARING CLEARANCE in this article.
Once clearance is checked, lubricate journals and bearings.
Install bearing caps. Ensure marks are aligned on connecting rod and
cap. Tighten rod nuts or bolts to specification. Ensure rod moves
freely on crankshaft. Check connecting rod side clearance. See
CONNECTING ROD SIDE CLEARANCE in this article.
CONNECTING ROD SIDE CLEARANCE
Position connecting rod toward one side of crankshaft as far
as possible. Using feeler gauge, measure clearance between side of
connecting rod and crankshaft. See Fig. 18. Clearance must be within
specifications.

length of cylinder block at several points.
If warpage exceeds specifications, deck must be resurfaced.
If warpage exceeds manufacturer's maximum tolerance for material
removal, replace block.
DECK HEIGHT
Distance from the crankshaft centerline to the block
deck is termed the deck height. Measure and record front and rear main
journals of crankshaft. To compute this distance, install crankshaft
and retain with center main bearing and cap only. Measure distance
from the crankshaft journal to the block deck, parallel to the
cylinder centerline.
Add one half of the main bearing journal diameter to distance
from crankshaft journal to block deck. This dimension should be
checked at front and rear of cylinder block. Both readings should be
the same.
If difference exceeds specifications, cylinder block must be
repaired or replaced. Deck height and warpage should be corrected at
the same time.
MAIN BEARING BORE & ALIGNMENT
For checking main bearing bore, remove all bearings from
cylinder block and main bearing caps. Install main bearing caps in
original location. Tighten bolts to specification. Using inside
micrometer, measure main bearing bore in 2 areas 90 degrees apart.
Determine bore size and out-of-round. If diameter is not within
specification, block must be align-bored.
For checking alignment, place a straightedge along centerline
of main bearing saddles. Check for clearance between straightedge and
main bearing saddles. Block must be align-bored if clearance is
present.
EXPANSION PLUG REMOVAL & INSTALLATION
Removal
Drill a hole in the center of expansion plug. Remove with
screwdriver or punch. Use care not to damage sealing surface.
Installation
Ensure sealing surface is free of burrs. Coat expansion plug
with sealer. Use a wooden dowel or pipe of slightly smaller diameter,
install expansion plug. Ensure expansion plug is evenly located.
OIL GALLERY PLUG REMOVAL & INSTALLATION
Removal
Remove threaded oil gallery plugs using the appropriate
wrench. Soft, press-in plugs are removed by drilling into plug and
installing a sheet metal screw. Remove plug with slide hammer or
pliers.
Installation
Ensure threads or sealing surface is clean. Coat threaded oil
gallery plugs with sealer and install. Replacement soft press-in plugs
are driven in place with a hammer and drift.
CAMSHAFT
* PLEASE READ THIS FIRST *

lightly into its seat. Using seal installer, fully seat seal in
bearing cap or cylinder block.
Trim seal ends even with block parting surface. Some
applications require sealer to be applied on main bearing cap prior
to installation. See Fig. 28.
Fig. 28: Typical Rope Seal Installation
This Graphic For General Information Only
Split-Rubber Type Seal
Follow manufacturers procedures when installing split-rubber
type rear main oil seals. Installation procedures vary with engine
type. See appropriate ENGINE article in this section. See Fig. 29.
Fig. 29: Typical Split-Rubber Seal Installation
This Graphic For General Information Only
OIL PUMP

damaged.
Pump cover wear is measured using a straightedge and feeler
gauge. Pump is to be replaced if warpage or wear exceeds
specifications or mating surface of pump cover is scratched or
grooved.
Fig. 33: Measuring Oil Pump Gear Cavity - Typical
This Graphic For General Information Only
BREAK-IN-PROCEDURE
* PLEASE READ THIS FIRST *
NOTE: Always refer to appropriate engine overhaul article in the
ENGINES section for complete overhaul procedures and
specifications for the vehicle being repaired.
ENGINE PRE-OILING
Engine pre-oiling should be done prior to operation to
prevent engine damage. A lightly oiled pump will cavitate unless oil
pump cavities are filled with engine oil or petroleum jelly.

\003
EN G IN E R EM OVA L - 4 -C YL

1988 J e ep C hero ke e
1988 ENGINES
Jeep - Engine Removal - 4-Cylinder
Cherokee, Comanche, Wrangler
4-CYLINDER ENGINES
2.5L
1) Disconnect negative battery cable. Drain cooling system.
Remove air cleaner, lower radiator hose, fan shroud, and engine
compartment light from hood. Scribe hinge locations and remove hood.
Disconnect automatic transmission cooler lines at radiator (if
equipped).
2) Remove upper radiator hose, fan assembly and coolant
recovery hose. Remove radiator and A/C condenser (if equipped). Hold
fan pulley to water pump flange using 5/16" x 1/2" SAE capscrew.
Disconnect heater hoses, throttle linkages, cruise control cable (if
equipped) and Throttle valve rod.
3) Disconnect wires from starter and separate CEC system
wiring harness connector. Disconnect fuel pipe from fuel pump and fuel
return hose from fuel filter. Disconnect hoses from A/C compressor and
power steering pump (if equipped). Drain power steering pump
reservoir. Cap all fittings and hose ends.
4) Remove vacuum check valve from brake booster (if
equipped). Tag and remove all wiring and vacuum lines connected to
engine or accessories. Raise vehicle and remove starter. Disconnect
exhaust pipe from manifold.
5) Remove converter/flywheel housing cover. Remove engine
mount nuts at bracket side. On automatic transmission models, index
mark drive plate and torque converter. Remove drive plate-to-converter
bolts.
6) Remove upper and loosen lower bellhousing-to-engine bolts.
Attach lifting equipment to engine. Raise engine off front mounts,
Place support under bellhousing. Remove remaining bellhousing-to-
engine bolts. Lift engine out of engine compartment.
NOTE: Engine mount pads may be removed from engine brackets to
align engine and transmission during installation.
TORQUE SPECIFICATIONS
TORQUE SPECIFICATIONS TABLE








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Application Ft. Lbs. (N.m)
Clutch Housing-to-Block Bolts .................... 55 (75)
Drive Plate-to-Converter ......................... 26 (35)
Flywheel Bolts ............................... ( 1) 50 (68)
Front Support Bracket-to-Block ................... 45 (61)
Front Support Cushion-to-Crossmember ............. 33 (45)
Rear Support Bracket-to-Transmission ............. 33 (45)
Rear Support Cushion-to-Bracket .................. 30 (41)
Starter Motor-to-Block ........................... 33 (45)
( 1) - Tighten an additional 60 degrees.









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\003
EN G IN E R EM OVA L - 6 -C YL

1988 J e ep C hero ke e
1988 ENGINES
Jeep - Engine Removal - 6-Cylinder
Cherokee, Comanche, Wagoneer, Wrangler
6-CYLINDER ENGINES
4.0L
1) Scribe hinge locations, remove engine compartment light
(if equipped) and remove hood. Disconnect battery cables and remove
battery. Drain cooling system.
2) Disconnect wire connectors from alternator, ignition coil
and distributor. Disconnect oil pressure sender wire, starter wires
and fuel injector wiring harness (if equipped). Detach 2 fuel pipe
quick connect couplings at left inner fender panel. Disconnect engine
ground strap and remove air cleaner.
3) Disconnect the vacuum purge hose at fuel vapor canister
tee. Disconnect wire from idle speed actuator and oxygen sensor.
Detach throttle cable from bracket and disconnect throttle valve rod
at bellcrank. Remove upper and lower radiator hoses.
4) On automatic transmission models, disconnect the
transmission fluid cooler tubing. On all models, remove fan shroud and
radiator. Remove fan and spacer or Tempatrol fan assembly. Hold fan
pulley to water pump flange using 5/16" x 1/2" SAE capscrew while
crankshaft is rotated.
5) Disconnect cruise control cable (if equipped). Disconnect\
wires from starter motor solenoid and disconnect CEC system harness.
Remove power brake vacuum check valve from booster (if equipped).
6) Disconnect power steering hoses from steering gear (if
equipped). Drain power steering pump reservoir and plug end of hoses.
Cap all fittings on steering gear and hoses. Raise and support
vehicle. Remove starter. Remove flywheel housing access cover.
7) Remove upper and loosen lower bellhousing-to-engine bolts.
Attach lifting equipment to engine. Raise engine off front mounts.
Place support under bellhousing. Remove remaining bellhousing-to-
engine bolts. Lift engine out of engine compartment.
4.2L
1) Remove battery and drain cooling system. Remove air
cleaner and engine compartment light from hood. Scribe hinge location
and remove hood. Disconnect and plug front fuel line at pump and fuel
return line at frame.
2) Disconnect heater hoses at heater. Label and disconnect
all wiring, lines, linkage and hoses at engine. Remove vacuum switch
assembly bracket from cylinder head cover. Remove both radiator hoses
and automatic transmission oil lines (if equipped) at radiator. Remove\
radiator and shroud.
3) Remove fan and spacer. Use 5/16" x 1/2" SAE bolt to hold
fan pulley to water pump flange. Remove starter and disconnect engine
ground strap. Remove engine mount-to-bracket nuts. Disconnect exhaust
pipe at manifold.
4) Discharge A/C system (if equipped). Disconnect and plug
hose or port openings at compressor. Disconnect hoses at power
steering gear and drain reservoir. Remove power brake vacuum check
valve. Remove bracket bolt for automatic transmission filler tube (if
equipped).
5) Lift and support vehicle. On models with automatic

ECU is a digital microprocessor computer. Data sensors
provide the ECU with engine operating information in varying
electrical signals. ECU calculates this information and corrects
air/fuel ratio, ignition timing, and emission control as needed to
maintain efficient engine operation. Other ECU output signals control
upshift indicator light (manual transmission only), ignition module
dwell and A/C clutch operation.
UPSHIFT INDICATOR
On vehicles equipped with a manual transmission, ECU
controls upshift indicator light. Indicator light is normally
illuminated when ignition is turned on without engine running.
Indicator light is turned off when engine is started.
Indicator light will be illuminated during engine operation
in response to engine load and speed. If transmission is not shifted,
ECU will turn light off after 3 to 5 seconds. A switch located on
transmission prevents indicator light from being illuminated when
transmission is shifted to highest gear.
DATA SENSORS & SWITCHES
Manifold Absolute Pressure (MAP) Sensor
MAP sensor is located in engine compartment on firewall,
behind engine. MAP sensor monitors manifold vacuum via a vacuum line
from intake manifold to sensor.
MAP sensor supplies an electrical signal which keeps ECU
informed of manifold vacuum and barometric pressure conditions. This
information is combined with data supplied by other sensors to
determine correct air/fuel ratio.
Oxygen Sensor
Oxygen (O2) sensor is mounted in exhaust manifold where it
is exposed to exhaust gas flow. Its function is to monitor oxygen
content of exhaust gases and to supply ECU with a voltage signal
directly proportional to this content.
If oxygen content of exhaust gases is high (lean air/fuel
mixture), voltage signal to ECU is low. As oxygen content decreases
(mixture becomes richer), signal voltage increases.
In this way, ECU is kept constantly informed of air/fuel
ratio. ECU can then alter fuel injector "on" time, in response to
these signals, to obtain best air/fuel ratio of 14.7:1 under any
given operating conditions.
O2 sensor is equipped with a heating element that keeps
sensor at proper operating temperatures. Maintaining correct sensor
temperatures at all times guarantees a more accurate signal to ECU.
By using an O2 heater, fuel control system may also enter "closed
loop" operating mode sooner and maintain this mode, even during
periods of extended idle.
Temperature Sensors
There are 2 temperature sensors used on this system.
Manifold Air Temperature (MAT) sensor, mounted in intake manifold,
measures temperature of incoming air/fuel mixture and Coolant
Temperature Sensor (CTS), located on left side of cylinder block just
below the exhaust manifold, measures temperature of engine coolant.
Information provided by these 2 sensors to ECU allows ECU to
demand slightly richer air/fuel mixtures and higher idle speeds
during cold engine operation.
Throttle Position Sensor (TPS)
TPS is regulated by movement of throttle shaft. It is