1988 JEEP CHEROKEE lock

Improper gate plate See STEERING COLUMN
adjustment article









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Excess Play in Instrument panel bracket Tighten bolts and check
Column bolts loose bracket
Broken weld nut on jacket See STEERING COLUMN
article
Instrument bracket capsule See STEERING COLUMN
sheared article
Column bracket/jacket Tighten bolts and check
bolts loose bracket









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Steering Locks Release lever mechanism See STEERING COLUMN
in Gear article









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SUSPENSION TROUBLE SHOOTING
NOTE: This is GENERAL information. This article is not intended
to be specific to any unique situation or individual vehicle
configuration. The purpose of this Trouble Shooting
information is to provide a list of common causes to
problem symptoms. For model-specific Trouble Shooting,
refer to SUBJECT, DIAGNOSTIC, or TESTING articles available
in the section(s) you are accessing.
BASIC SUSPENSION TROUBLE SHOOTING CHART









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CONDITION POSSIBLE CAUSE CORRECTION








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Front End Noise Loose or worn wheel See Wheel Bearing
Adjustment in
SUSPENSION
Worn shocks or shock Replace struts or strut
mountings mountings
Worn struts or strut Replace struts or strut
mountings mountings
Loose or worn lower control See SUSPENSION
arm
Loose steering gear-to- See STEERING
frame bolts
Worn control arm bushings See SUSPENSION
Ball joints not lubricated Lubricate ball joints &
see Ball Joint Checking
in SUSPENSION









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Front Wheel Tires or wheels out of Check tire balance
Shake, Shimmy, balance
or Vibration
Incorrect wheel alignment See WHEEL ALIGNMENT
Drive shaft unbalanced Check drive shaft
balance

\003
TU NE-U P - 6 -C YL

1988 J e ep C hero ke e
1987-88 TUNE-UP
Jeep 6 Cylinder Tune-Up
Cherokee, Comanche, Wagoneer, Wrangler
IDENTIFICATION
ENGINE IDENTIFICATION
Engine can be identified by the fourth character of engine
Build Date Code number, located on a tag attached to right side of
block between No. 2 and 3 cylinders.
The same code letter is also the fourth character in the
Vehicle Identification Number (VIN), located at top left corner of
dashboard.
ENGINE CODE TABLE









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Engine Code
4.0L (242") MPFI ....................................... M
4.2L (258") 2-Bbl. ..................................... C









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TUNE-UP NOTES
NOTE: When performing tune-up procedures described in this
article, these notes and precautions must be followed.
Due to late changes and corrections, always refer to Emission
Control Label in engine compartment before attempting tune-up. If
manual and label specifications differ, use label specifications.
When performing tune-up on vehicles equipped with a catalytic
converter, do not allow or create an engine misfire in one or more
cylinders for an extended period of time. Damage to converter from
overheating may occur due to loading with unburned fuel.
TESTING
ENGINE COMPRESSION
Check compression pressure with engine at normal operating
temperature, all spark plugs removed, throttle and choke valves wide
open and engine at cranking speed.
COMPRESSION SPECIFICATIONS TABLE









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Application Specification
Compression Ratio .................................. 9.2:1
Compression Pressure ....... 120-150 psi (8.4-10.5 kg/cm
)
Maximum Variation Between Cylinders .. 30 psi (2.1 kg/cm)








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HIGH TENSION WIRE RESISTANCE
Do not puncture spark plug wires with any type of probe.
Remove spark plug wire and check resistance using an ohmmeter.

wires connected to switch). Disconnect distributor vacuum advance hose
and connect hose to vacuum switch. Disconnect wire connector from
knock sensor, located in cylinder head.
3) Using a jumper wire, ground knock sensor wire connector to
engine block. Start engine. With engine at idle speed (solenoid
energized), check timing. Adjust timing to one degree more than
specification (if required). See Emission Control Label.
IGNITION TIMING SPECIFICATIONS (DEGREES BTDC@RPM) - 4.2L









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Application Man. Trans. Auto. Trans.
50 State ............. 9 @ 1600 ............... 9 @ 1600
High Altitude ........ 16 @ 1600 ............. 16 @ 1600









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HOT (SLOW) IDLE RPM
4.0L
1) Apply parking brake and place transmission in Neutral
(Drive for automatic transmissions). Operate engine to normal
operating temperature. Turn ignition off.
2) Ensure all accessories are off. Connect positive
tachometer lead to terminal "D1-1" and negative lead to "D2-7" of
diagnostic connectors. See Fig. 3. Disconnect air stepper motor
connector and TPS wiring connector. See Fig. 4.
Fig. 3: Diagnostic Connector Terminal Identification
Courtesy of Chrysler Motors.

or vehicle fails emissions testing.
IDLE MIXTURE (TACHOMETER (LEAN DROP) PROCEDURE)
NOTE: On 4.2L engines, ensure idle speed and timing are set prior
to adjusting the idle mixture. If mixture adjustment time
exceeds 3 minutes, run engine at 2000 RPM in Neutral for one
minute, and resume adjustment. On 4.0L engines, idle mixture
adjustment is not possible.
4.2L
1) Remove carburetor and locate roll pins blocking idle
mixture screws. Drill through throttle body on closed end of roll pin
hole. Drive pins out with punch. Reinstall carburetor. Install
tachometer.
2) Operate engine to normal operating temperature, and adjust
curb idle speed. Place automatic transmission selector in Drive
(Neutral for manual transmissions). Turn mixture screws inward until
RPM drops. Turn screws outward until highest RPM is reached.
3) Turn mixture screws inward to obtain the correct decrease
in RPM. See LEAN DROP (RPM) table. Adjust both screws equally. When
mixture is correctly adjusted, replace roll pin to block adjustment
screws.
NOTE: If final RPM differs more than 30 RPM from specified curb
idle speed, reset curb idle, and repeat mixture adjustment.
LEAN DROP (RPM) TABLE









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Application Man. Trans. Auto. Trans.
4.2L .................... 50 ........................ 50









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THROTTLE POSITION SENSOR (TPS)
NOTE: Adjustment of TPS only applies to the 4.0L models. It may be
necessary to remove throttle body from intake manifold, to
access sensor wiring harness.
Checking & Adjusting - 4.0L (Automatic Transmission)
1) Locate the square TPS connector. Note connector terminal
identification stamped on the back of the connector. Turn ignition on.
2) Connect voltmeter through back of wiring harness
connector. Connect negative voltmeter lead to terminal "D" and
positive voltmeter lead to terminal "A" to check input voltage. DO NOT
disconnect TPS connector.
3) Hold throttle plate closed against idle stop and note
voltage. Input voltage should be approximately 5 volts. Disconnect
voltmeter positive lead and connect to terminal "B" to measure output
voltage.
4) With throttle plate closed, measure the output voltage.
The output voltage should be approximately 4.2 volts. If output
voltage is not within specification, loosen TPS retaining screws.
5) Partially tighten one retaining screw. Rotate TPS to
obtain correct output voltage. Tighten retaining screws once correct
voltage is obtained.
Checking & Adjusting - 4.0L (Manual Transmission)
1) Turn ignition on. Connect voltmeter through back of wiring
harness connector. Connect negative voltmeter lead to terminal
"B" and positive voltmeter lead to terminal "A". DO NOT disconnect TPS
connector.

TU RN S IG NALS & H AZA R D F LA SH ER S

1988 J e ep C hero ke e
1988 Turn Signal & Hazard Light Systems
JEEP
DESCRIPTION
Turn signals and hazard flashers systems use a common turn
signal/hazard light switch assembly mounted within upper steering
column housing.
FLASHER LOCATIONS
Hazard
Mounted on fuse block.
Turn Signal
Mounted on fuse block.
TROUBLE SHOOTING
NOTE: Following trouble shooting is only information available
from manufacturer.
Hazard Lights (Comanche, Cherokee & Wagoneer)
If lights do not come on with hazard switch turned on, check
hazard/stop light fuse by operating stop lights. If fuse is okay,
check turn signal flasher, turn signal/hazard switch, and related
wiring. If only one hazard light does not work, check bulb.
Turn Signals (Comanche, Cherokee & Wagoneer)
If all turn signals do not work, check turn/back-up light
fuse by operating back-up lights. If fuse is okay, check turn signal
flasher, turn signal/hazard switch, and related wiring. If only one
turn signal does not work, check bulb.
TESTING
NOTE: Following trouble shooting is only information available
from manufacturer.
Hazard Indicators (Wrangler)
1) Turn ignition and hazard warning switch "ON". Check for
pulsating voltage at Light Blue (left indicator) and Dark Blue (right\
indicator) wires. If voltage is present, go to next step. If voltage
is not present, replace turn signal switch.
2) Remove bulbs for turn signal indicators. Measure
resistance across bulb terminals. If resistance is zero ohms, replace
light bulb(s). If resistance readings are not zero ohms, go to next
step.
3) Check for pulsating voltage at battery side of bulb
sockets. If voltage is present, go to next step. If voltage is not
present, repair open circuit between socket and turn signal switch
steering column connector.
4) Turn ignition off and check resistance on ground side of
bulb sockets. If resistance is zero ohms, hazard indicator circuit is
okay. If resistance reading is not zero ohms, repair open in ground
circuit.
Hazard Lights (Wrangler)

1) Check operation of stop lights. If stop lights come on, go
to next step. If not, check hazard/stop light fuse. If fuse is okay,
check for voltage on battery side of hazard/stop light fuse. If
voltage is not present, repair open circuit between fusible link and
fuse block.
2) Remove hazard flasher and check for voltage on battery
side of hazard flasher at fuse block. If voltage is present, go to
next step. If voltage is not present, repair open circuit to fuse
block.
3) Measure resistance across turn signal flasher terminals.
If resistance across flasher is zero ohms, replace flasher. If
resistance is other than zero ohms, install flasher and turn ignition
on.
4) Check for voltage at Brown wire of turn signal switch
steering column connector. If voltage is present, go to next step. If
voltage is not present, repair open circuit between flasher and turn
signal switch connector.
5) Turn hazard warning switch "ON". Check for pulsating
voltage at Light Blue, Dark Blue, Yellow, and Dark Green wires. If
voltage is present, hazard light circuit is okay. If voltage is not
present, replace turn signal switch.
Turn Signals (Wrangler)
1) Turn ignition on and check operation of back-up lights. If
lights come on, go to step 3). If back-up lights do not come on, check
turn signal/back-up light fuse.
2) If fuse is okay, check for voltage at battery side of turn
signal/back-up light fuse. If voltage is not present, repair open
circuit between fuse block and ignition switch. If voltage is present,
go to next step.
3) Remove turn signal flasher and measure resistance across
flasher terminals. If resistance across flasher is zero ohms, replace
turn signal flasher. If flasher is okay, install flasher and turn
ignition on.
4) Check for voltage on battery side of flasher at fuse
block. If voltage is present, go to next step. If voltage is not
present, repair open circuit to fuse block.
5) Disconnect turn signal switch at steering column
connector. Place turn signal switch in left turn position and measure
resistance between Yellow and Purple wires. If resistance across wires
is zero ohms, replace turn signal switch. If resistance is other than
zero ohms, go to next step.
6) Place turn signal switch in right turn position and
measure resistance between Dark Green and Purple wires. If resistance
across wires is zero ohms, replace turn signal switch. If resistance
is other than zero ohms, turn signal circuit is okay.
Turn Signal Indicators (Wrangler)
1) Turn ignition on. Place turn signal switch in left turn
position and check for pulsating voltage at Light Blue wire. If
voltage is present, go to next step. If voltage is not present,
replace turn signal switch.
2) Place turn signal switch in right turn position and check
for pulsating voltage at Dark Blue wire. If voltage is not present,
replace turn signal switch. If voltage is present, go to next step.
3) Remove bulbs from turn signal indicators. Measure
resistance across bulb terminals. If resistance is zero ohms, replace
light bulb(s). If resistance readings are not zero ohms, turn ignition\
on.
4) Place turn signal switch in left and right turn position
and check for pulsating voltage at battery side of bulb sockets. If
voltage is present, go to next step. If voltage is not present, repair
open circuit between socket(s) and steering column connector.

3) Remove cross shaft assembly from yoke. DO NOT remove seal
retainers from cross shaft. Cross shaft and retainers are serviced as
an assembly.
Reassembly
1) Coat roller and bearing assemblies with lubricant, and
fill reservoirs in ends of cross. Place cross assembly in drive shaft
yoke, and place roller and bushing assemblies into position.
2) Press both bushing assemblies into yoke until retainers
can be installed, being careful to keep cross aligned in center of
bushings. Install retainers, then repeat procedure for remaining
bushings.
CONSTANT VELOCITY (CV) TYPE
NOTE: To prevent damage to constant velocity joints, center ball
when removing drive shaft assembly. When handling drive shaft
after removal, support shafts on both sides of constant
velocity joint if drive shaft is being moved horizontally.
DO NOT allow one end to hang free or one shaft to bend at
sharp angle. After removal, shaft may be carried vertically
without damage.
Removal & Disassembly (Jeep)
1) Disconnect yoke attaching bolts and flange attaching
bolts, and remove drive shaft from vehicle. Mark joint so that center
yoke, end yoke, and cross shafts will be installed in original
positions.
2) Pry out all snap rings and press bearing out enough to
allow bearing end to be clamped in vise. Tap on yoke until it is free
of bearing.
3) Repeat procedure for remaining bearings. Remove remaining
parts from center yoke assembly.
Reassembly
1) Pack all bearings with specified grease. Assemble center
yoke components in reverse order of disassembly.
2) Using arbor press or vise, press 2 opposing bearings into
osition at same time until all bearings are installed. Be sure cross
shafts and yokes remain aligned during this process.
3) Check for free movement of joint. If bind exists, seat
bearings by sharply rapping yokes with brass hammer. Never hammer on
bearings.
4) Install drive shaft in vehicle, making sure marks made
during disassembly are aligned.
Installation (All Models)
NOTE: The drive shaft assembly, with cross and bearings installed,
must have its yoke ears at each end of the shaft on same
plane.
1) Before installing drive shaft, clean yoke and inspect
machined surface for scratches, nicks or burrs.
2) Provide support for drive shaft during installation to
prevent damage to universal joints. Position front end of shaft and
aligning marks noted during removal.
3) Install and attach 2 clamps to pinion yoke. Install 4
screws and lock washer assemblies on CV joint at transfer case. Use
press bar to prevent assembly from rotating while attaching screw
assemblies.

or backward tilt from vertical is viewed from side of vehicle. When
axis is tilted backward from vertical, caster is said to be positive,
creating a trailing action on front wheels. When axis is tilted
forward, caster is negative, causing a leading action on front wheels.
Fig. 2: Caster Angle
TOE
Toe is the measured difference in inches of distance between
the front edge of the tires and the rear edge of the tires at spindle
height. Toe can be measured in inches or degrees.
ADJUSTMENT
TOE
1) Measure toe with front wheels straight-ahead and steering
wheel locked in a centered position. Adjust toe by loosening clamps
and adjusting sleeve or adjusting ends on right and left tie rods
equally and in opposite directions to maintain steering wheel in
centered position.
2) If steering wheel is not centered to begin with,
determine which tire assembly is toed in or out more than the other