1988 JEEP CHEROKEE change time

Removal
1) Remove PCV valve hose at valve cover. Remove valve cover
bolts. Using a razor knife, cut RTV sealant along valve cover. Pry
upward on valve cover in areas marked "PRY HERE" near bolt hole areas.
2) Remove valve cover. Alternately loosen each rocker arm
bolt one turn at a time. Remove rocker arm assemblies and push rods.
Mark components for reassembly. Components must be installed in
original location.
Installation
Reverse removal procedures. Install rocker arm components in
original location. Tighten bolts to specification. Apply RTV sealant
on valve cover prior to installation.
VALVE SPRINGS
Valve springs can be removed without removing cylinder head.
Valve Spring Installed Height
Information not available from manufacturer.
HYDRAULIC VALVE LIFTERS
Removal
Remove rocker arms and push rods. See ROCKER ARMS & BRIDGE.
Using Lifter Remover/Installer (J-21884), remove lifter through push
rod openings of cylinder head. Mark lifter location for reassembly
reference. Replace lifters as an assembly if damaged. Internal
components cannot be interchanged.
Inspection
Inspect lifter and camshaft mating surfaces for wear. Check
cylinder block lifter bore diameter. Lifter bore diameter should be
within .9055-.9065" (22.999-23.025 mm). Replace parts as necessary.
Installation
Soak lifter assembly in engine oil supplement prior to
installation. Reverse removal procedures for installation. Install
lifter in original location.
ENGINE FRONT COVER
Removal
1) Disconnect negative battery cable. Remove drive belts, fan
and hub assembly. Remove pulley from vibration damper. Remove
vibration damper retaining bolt and washer.
2) Using Puller (J-21719-01), remove vibration damper and
key. Remove oil pan-to-front cover bolts. Remove cover-to-block
retaining bolts. Remove front cover.
3) Cut oil pan gasket even with face of cylinder block.
Remove gasket from oil pan. Pry crankshaft oil seal from cover.
Installation
1) Ensure all gasket surfaces are clean. Ensure oil slinger
is installed on crankshaft. Apply sealing compound on both sides of
front cover gasket. Install gasket on cylinder block. Replace front
section of oil pan seal with similar section fabricated from new seal.
2) Coat seal with RTV sealant and place in position. Apply
sealant to the joint area of oil pan and cylinder block. Place front
cover on cylinder block. Place Front Cover Seal Installer (J-22248) in\
front cover seal area.
3) Install all retaining bolts. Tighten bolts to

input sensors. During engine start-up, the injector delivers an extra
amount of fuel to aid in starting.
EMISSION CONTROL
Both EGR and canister purge operation are regulated by the
ECU. Regulation of these 2 systems is accomplished through the use of
an electrically-operated vacuum solenoid.
Whenever the solenoid is energized by the ECU, it prevents
vacuum action on the EGR valve and canister. The solenoid is
energized by the ECU during engine warm-up, improving cold
driveability. It is also energized during closed throttle (idle),
wide open throttle and during rapid acceleration or deceleration.
In this way the EGR is prevented from operating until the
engine reaches a predetermined temperature. The canister purge does
not operate until the oxygen sensor warms up and becomes operational.
This prevents an over-rich mixture until the oxygen sensor can
compensate for the extra fuel vapor.
IDLE SPEED ACTUATOR (ISA)
The ISA motor, located on the throttle body, is an
electrically-driven actuator that changes the throttle stop angle by
acting as a movable idle stop. The ECU commands the ISA to control
engine idle speed and maintain a smooth idle during sudden engine
deceleration. It does this by providing the appropriate voltage
outputs to produce the idle speed or throttle stop angle required for
the particular engine operating condition. There is no idle speed
adjustment.
For cold engine starting, the throttle is held open for a
longer period to provide adequate engine warm-up prior to normal
operation. When starting a hot engine, the throttle is open for
shorter time.
Under normal engine operating conditions, engine idle is
maintained at a pre-programmed RPM, which may vary slightly due to
engine operating conditions. Under certain engine deceleration
conditions, the throttle is held slightly open.
IGNITION ADVANCE CONTROL
Under certain engine operating conditions, the predetermined
ignition advance curve is modified. This is accomplished through 2
switching circuits that connect the ECU and the ignition control
module.
ECU-CONTROLLED RELAYS
System Power Relay
Located on the right strut tower, this relay is energized
during engine start up and remains energized until 3 to 5 seconds
after the engine is stopped. This permits the ECU to extend the idle
speed actuator for the next start up and then cease operation. See
Fig. 4.

\003
4.0 L C EC S YSTE M

1988 J e ep C hero ke e
1988 COMPUTERIZED ENGINE Controls
ENGINE CONTROL SYSTEM
JEEP 4.0L MPFI 6-CYLINDER
Cherokee, Comanche & Wagoneer
DESCRIPTION
The 4.0L engine control system controls engine operation to
lower exhaust emissions while maintaining good fuel economy and
driveability. The system is designed to maintain a 14.7:1 air/fuel
ratio under all engine operating conditions. When the ideal air/fuel
ratio is maintained, the catalytic converter can control oxides of
nitrogen (NOx), hydrocarbon (HC), and carbon monoxide (CO) emissio\
ns.
The system consists of the following sub-systems: Fuel
Control, Data Sensors and Switches, Electronic Control Unit (ECU),
Diagnostics, Electronic Spark Advance, Idle Speed Control, Exhaust Gas
Recirculation, and Transmission Shift Light.
OPERATION
FUEL CONTROL
The fuel control system delivers fuel to the engine. Fuel
from the in-tank fuel pump flows to the fuel rail, injectors and
pressure regulator. The pressure regulator maintains fuel system
pressure at 31-39 psi (2.l-2.7 kg/cm
). Excess fuel is returned to the
tank by a fuel return line.
The fuel pump is energized through the fuel pump relay that
is located on the right inner fender panel in the engine compartment.
Battery voltage is provided through the ignition switch and is
energized when the ECU completes the ground path.
The fuel injectors are electrically operated solenoid valves.
The ECU determines injector pulse width ("on/off") time based upon
engine operating conditions and delivers the proper pulse width to
maintain an air/fuel ratio of 14.7:l.
The ECU varies the amount of voltage applied to the injectors
to compensate for battery voltage changes. Battery voltage information
is provided to the ECU through the wiring harness. No sensor or switch
is required.
DATA SENSORS & SWITCHES
Each sensor and/or switch furnishes electronic impulses to
the ECM. Based on these input signals, the ECM computes spark timing
and air/fuel mixture for proper engine operation.
Coolant Temperature Sensor (CTS)
The CTS is located on the left side of the block, just below
exhaust manifold. The sensor provides coolant temperature information
to the ECU. Engine coolant temperature is used by the ECU for the
following functions:
* Enrich air/fuel mixture for cold engine starts.
* Control idle speed during warm-up.
* Increase spark advance during cold engine operation.
* Prevent EGR flow during cold engine operation.

2) Loosen discharge port valve slightly. Loosen valve port
cap to allow refrigerant to force out air from compressor. Back-seat
the discharge valve and tighten the port cap. Compressor is ready for
service.
REFRIGERATION OIL
Only new, pure, moisture-free refrigeration oil should be
used in the air conditioning system. This oil is highly refined and
dehydrated (moisture content less than 10 parts per million).
Refrigeration oil container must be kept tightly closed at
all times when not in use, or moisture will be absorbed from the air
and introduced into the refrigeration system.
NIPPONDENSO 10-CYLINDER
SHAFT SEAL
NOTE: Check compressor refrigerant oil level when replacing seals.
See COMPRESSOR REFRIGERANT OIL CHECKING article in this
section.
Removal
1) Hold clutch hub stationary and remove center nut. Screw
remover into center of hub. Turn center bolt to remove pressure plate.
2) Remove shims from shaft. Remove snap ring from inside of
pulley. Tap pulley off of shaft with plastic mallet. Be careful not
to distort pulley while removing.
3) Disconnect clutch coil wires from compressor housing.
Remove snap ring inside coil and lift coil off compressor. Pry dust
seal out from around compressor shaft (if equipped).
4) Place shaft key remover on shaft and turn to remove key.
Remove drain plug (if equipped). Remove bolts holding service valves
to body of compressor and remove valves. Discard "O" rings. Drain oil
out of compressor.
5) Remove 6 through bolts from front head of compressor and
discard washers. Tap head loose from compressor, being careful not to
scratch sealing surfaces. Remove snap ring (if equipped) from front
housing. Press seal plate out. Remove seal from shaft. See Fig. 1.
Installation
1) Lubricate shaft seal with clean refrigerant oil. Place on
compressor shaft. Lubricate seal plate (and "O" ring, if equipped) and\
install in front housing. Install snap ring (if equipped).
2) Place front housing on compressor body. Using new
washers, install through bolts. Tighten bolts evenly and alternately
to 18 ft. lbs. (24 N.m). Install shaft key with installer and plastic
mallet. Insert dust seal into front of compressor.
3) Install drain plug using new gasket. Add correct amount
of refrigerant oil to compressor. If service valves were removed,
coat new "O" rings with refrigerant oil and install service valves.
4) Place clutch coil on compressor and install snap ring.
Install shims on shaft to adjust clearance between pressure plate and
rotor to .016-.028" (.41-.71 mm). Tighten shaft nut to 12 ft. lbs. (1\
6
N.m). See REFRIGERANT OIL & R-12 SPECIFICATIONS table for system
capacities.
SANKYO/SANDEN 5-CYLINDER COMPRESSOR SERVICING
NOTE: During the past year, Sankyo International (USA), Inc. has
changed its name to Sanden International (USA), Inc.

be obtained. During high speeds "on" time may be 10 percent and "off"
time 90 percent. During low speeds with high electrical loads, "on"
time may be 90 percent and "off" time 10 percent.
SI SERIES
A rectifier bridge, connected to stator windings, contains 6
diodes (3 positive and 3 negative) molded into an assembly. This
rectifier bridge changes stator AC voltage into DC voltage, which
appears at output terminal.
Alternator field current is supplied through a diode trio
which is also connected to stator windings. A capacitor is mounted to
end frame, protecting rectifier bridge and diodes from high voltage
and suppressing radio interference noise.
TROUBLE SHOOTING
NOTE: See the TROUBLE SHOOTING - BASIC PROCEDURES article
in the GENERAL TROUBLE SHOOTING section.
TESTING
PRELIMINARY INFORMATION
NOTE: Before making electrical checks, visually inspect all
terminals for clean, tight connections. Check alternator
mounting bolts and drive belt tension. Battery must be in
good condition to test charging system.
TESTING (ON-VEHICLE)
CS SERIES
Over/Undercharged Battery (W/ STandard Instruments)
1) If an overcharging condition is suspected, run engine at a
moderate speed. Connect a voltmeter across battery terminals. If
voltmeter indicates more than 16 volts, replace alternator.
2) If an undercharging condition is suspected, disconnect
2
wire connector from alternator. Turn ignition on with engine off.
Connect a voltmeter between terminal "L" in wiring harness and ground.
Record reading.
3) If terminal "I" is used, connect voltmeter between
terminal "I" and ground. Record reading. If voltmeter reads battery
voltage, circuits are okay. If voltmeter reads zero, this indicates an
open circuit between terminal checked and battery. Repair as
necessary.
Overcharged Battery (W/ Gauges)
If an overcharging condition is suspected, run engine at a
moderate speed. Connect a voltmeter across battery terminals. If
voltmeter indicates more than 16 volts, replace alternator.
Alternator Output Test (W/ Standard Instruments Or Gauges)
1) Run engine at moderate speed, all electrical accessories
off. Measure voltage across battery, if above 16 volts, replace
alternator.
2) Connect an ammeter in circuit at "BAT" terminal of
alternator. Turn on all available accessories. Connect a battery load
tester across battery. Operate engine at 2000 RPM and adjust battery
load tester as required to obtain maximum current output while

* CARTRIDGE ERROR
* HIGH BATTERY
* KEYPAD TEST FAILURE
* LOW BATTERY
* RAM TEST FAILURE
3) If no error messages appear, display will read as follows
after a few seconds: 1) VEHICLES TESTED, 2) HOW TO USE, 3) CONFIGURE
and 4) SELECT SYSTEM.
4) Select 4) SELECT SYSTEM to enter diagnostic system. Once
in SELECT SYSTEM, select 2) TRANSMISSION to enter transmission.
Display will read 1) EATX and 2) AW4.
5) Select 2) AW4. After a few seconds display will change to
read AW4, VERSION 01. After a few seconds, display will read AW4 MENU,
1) SYSTEM TEST and 2) READ FAULTS. If DOWN ARROW is depressed 3 times,\
display will read as follows: 3) STATE DISPLAY, 4) ACTUATOR TESTS and
5) ADJUSTMENTS.
NOTE: The ACTUATOR TESTS and ADJUSTMENTS cannot be used when
diagnosing the AW-4 transmission.
Retrieving Diagnostic Trouble Codes
1) Select 2) READ FAULTS from AW4 MENU. If no diagnostic
trouble code exists, display will read as follows: AW4 FAULTS, NO
FAULTS DETECTED.
2) If diagnostic trouble code exists, the following message
will be displayed: 1 OF 3 FAULTS. This number will vary depending on
number of diagnostic trouble codes stored in the TCM memory.
3) Diagnostic trouble code and message will be displayed.
Press DOWN ARROW key to display next diagnostic trouble code. To
identify diagnostic trouble code, see DIAGNOSTIC TROUBLE CODE
IDENTIFICATION table.
NOTE: See TROUBLE SHOOTING CHARTS to diagnose faults indicated by
trouble codes.
NOTE: Valve body solenoid diagnostic trouble code 700 may appear
in a FAULT PRESENT or FAULT STORED status. Status will be
displayed along with diagnostic trouble code. Diagnostic
trouble code must be diagnosed depending on the status. See
TEST 1A - VERIFICATION OF THE COMPLAINT under TROUBLE
SHOOTING CHARTS.
DIAGNOSTIC TROUBLE CODE IDENTIFICATION









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Trouble Code Problem Area
700 ( 1) .............................. Valve Body Solenoid
702 ......................................... Speed Sensor
703 ............................... ( 2) Gear Select Switch
705 ............................. Throttle Position Sensor
706 ......................................... Brake Switch
707 ..................................... Wrong TCM Or TCU
( 1) - Trouble code may apply to individual valve body
solenoids. Valve body solenoid may be referred to
as S1 for No. 1, S2 for No. 2 and S3 for No. 3.
( 2) - Gear select switch is the same as the neutral
safety switch.









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CLEARING DIAGNOSTIC TROUBLE CODES

PINION DEPTH
1) Depth Gauge Set (D-271) is used to determine pinion depth\
.
Place Master Pinion Block (D-139 on Model 44; D-120 on Model 60 and
61; D-137 on Model 70; T80T-4020-F42 on Model 80) in pinion bore of
carrier. Put Arbor Discs (D-115-4-44 on Model 44; D-116-2 on Models
60,61 and 70; (T88T-4020-A) on Arbor (D-115-3). Install arbor in
carrier with discs riding in bearing bore.
2) Put Pinion Height Block (D-115-1-44 on Model 44; D-116-1
on Models 60, 61, 70 and 80) on top of master pinion block with side
against arbor. Place Scooter Block (115-2) with Dial Indicator (D-106\
-
5) on small step of pinion height block. Zero dial indicator with
scooter block flat on pinion height block.
3) Move scooter block so dial indicator tip touches arbor.
Move block back and forth (perpendicular to arbor) to get highest
reading. This reading, plus or minus value etched on pinion head, is
thickness of shim pack necessary for pinion bearing.
4) On Model 80, Use Gauge Tube (D81T-4020-F51) and Gauge
Block (D81T-4020-F56) to determine required thickness of shim pack.
5) On all models, measure shims separately with micrometer.
If baffle is used, its thickness must be included in shim pack. This
is also true if slinger is used between inner bearing and head of
pinion shaft. Place pinion height shim pack in carrier bore for inner
bearing race. Drive bearing race into carrier, making sure cup is
fully seated.
PINION BEARING PRELOAD
1) Drive outer pinion bearing into carrier housing. Press
inner pinion bearing onto pinion shaft using Press Tube (C-3095-A).
Ensure bearing seats fully. Insert pinion shaft into carrier. Install
outer bearing, slinger (if equipped), flange, washer and nut.
NOTE: Pinion preload shims and oil seal should NOT be installed at
this time.
2) Using an INCH lb. torque wrench, tighten pinion nut until
10 INCH lbs. (1.13 N.m) rotational torque is required to move pinion
shaft. Recheck pinion depth with arbor and discs at this time. Place
pinion height block on face of pinion shaft.
3) Place dial indicator on small step of height block for
Model 44, 60 and 61 axles. Place dial indicator on high step of block
for Models 70 and 80 axles. Zero dial indicator and move it across
arbor to get highest reading. If reading is within .002" (.05 mm) of
etching on pinion face, pinion depth is correct.
NOTE: If pinion depth is not with .002" (.05 mm) of etched number
on face of pinion, shim pack under inner bearing race must
be changed before proceeding with differential settings.
4) Remove pinion nut, washer, flange, slinger and outer
bearing. Place preload shims (removed during disassembly) on pinion.
Install bearing and slinger. After lightly coating lips with gear oil,
install pinion seal in carrier housing. Install flange, washer and NEW
pinion nut. Tighten nut to specification. See TORQUE SPECIFICATIONS
table at end of this article.
5) Using an INCH lb. torque wrench, measure preload
(rotational torque) of pinion shaft. Rotational torque required to
keep pinion shaft turning freely and smoothly should be 20-40 INCH
lbs. (2.3-4.5 N.m). If preload needs to be increased, remove a few
shims and recheck. To decrease preload, add a few shims and recheck.
See Fig. 14 .

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