1988 JEEP CHEROKEE check engine

3) Remove rocker arms and push rods. See ROCKER ARMS &
BRIDGE under VALVES. Remove cylinder head bolts. Remove cylinder head.
Inspection
Inspect cylinder head for cracks or damage. Using
straightedge, check cylinder head for warpage in several areas. Repair
or replace cylinder head if warpage exceeds .002" (.05 mm) per each 6"\
(152 mm) or damage exists.
Installation
1) Ensure all gasket surfaces are clean. Clean carbon from
combustion chambers and tops of pistons. Apply sealant to both sides
of new cylinder head gasket. Install new gasket with the word "TOP"
upward. Ensure all holes are aligned.
2) Install cylinder head. Apply sealing compound to threads
of cylinder head bolt No. 8 prior to installation. See Fig. 2. Install
head bolts. Tighten all bolts in sequence (except No. 8) to 110 ft.
lbs. (149 N.m). Tighten No. 8 head bolt to 100 ft. lbs. (136 N.m). S\
ee
Fig. 2 .
3) Reverse removal procedures for remaining components. When
installing valve cover, use RTV sealant between cover and head.
Tighten bolts to specification.
4) Fill cooling system with temperature sending unit removed.
Allow trapped air to escape, then install sending unit. Refill and
purge cooling system. See COOLING SYSTEM AIR PURGE under ENGINE
COOLING.
Fig. 2: Cylinder Head Bolt Tightening Sequence
VALVES
Valve Arrangement
E-I-I-E-E-I-I-E (Front-to-rear).
Valve Guides
Valve guides are not replaceable. If clearance is excessive,
valve guides must be reamed to accommodate oversized stem valves.
ROCKER ARMS & BRIDGE

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

engine and connecting rod oil squirt hole should face camshaft side of
engine.
3) Install bearings. Check oil clearance and connecting rod
side play clearance. Reverse removal procedures for remaining
components. Tighten bolts to specification.
Fitting Pistons
1) Determine cylinder taper, wear and out-of-roundness and
piston clearance. For cylinder specifications, see CYLINDER, PISTON &
CONNECTING ROD SPECIFICATIONS table. If taper or out-of-roundness are
not within specification, hone or bore cylinders for installation of
new pistons.
2) Measure piston at right angle of the piston pin at the
center line of the pin. Compare reading to cylinder bore to determine
clearance. Mark fitted piston for cylinder location.
CYLINDER, PISTON & CONNECTING ROD SPECIFICATIONS TABLE









\









\









\









\









\









\






Application In. (mm)
Connecting Rod
Crankshaft Bore .......... 2.2080-2.2085 (56.083-56.095)
Pin Bore ................... .9288-.9298 (23.591-23.616)
Cylinder Bore
Diameter ................. 3.8751-3.8775 (98.427-98.488)
Out-of-Round ................................ .001 (.02)
Taper ....................................... .001 (.02)
Piston Pin Bore Diameter ..... .9308-.9313 (23.642-23.655)
Piston Pin Diameter .......... .9304-.9309 (23.632-23.644)
Piston-to-Cylinder Clearance ..... .0009-.0017 (.022-.043)









\









\









\









\









\









\






PISTON PIN REPLACEMENT
NOTE: Note direction of arrow on piston and oil squirt hole in
connecting rod prior to removal.
Removal
Position piston on Support (J-21872-1), Pin Pilot (J-21872-2\
)
and Driver (J-21872-3) on an arbor press. See Fig. 6. Press piston pin
from piston.
NOTE: Piston and pin must be at standard room temperature when
measuring fit. Piston pin should gravity-fall through the
piston at room temperature. Piston pin cannot be reused
after removal.
Inspection
Measure piston pin diameter, piston bore and connecting rod
bores. Replace components if not within specification. See CYLINDER,
PISTON & CONNECTING ROD SPECIFICATIONS table.
NOTE: Connecting rod must be positioned on the piston so the oil
squirt hole faces the camshaft side of the engine with
piston installed with arrow toward the front of the engine.
Installation
1) Insert pin pilot through piston and connecting rod. Place
assembly on support. Insert piston pin through the upper piston pin
bore and into connecting rod pin bore. See Fig. 6.

NOTE: Crankshaft journal diameters are indicated by a color coded
mark placed on the adjacent counterweight or cheek toward
the flanged (rear) end of crankshaft. Note color code to
determine proper bearing usage. Check oil clearance after
bearing installation.
Removal
1) Remove oil pan. See OIL PAN REMOVAL at end of ENGINE
section. See oil pump. See OIL PUMP under ENGINE OILING. Remove main
bearing cap.
2) Rotate crankshaft to position rod to be serviced at bottom
of stroke. Mark bearing cap and connecting rod. Remove bearing cap
with bearing. Push piston and rod assembly up to remove upper bearing.
Installation
1) Note color code on edge of bearings removed. Install
bearings. Using Plastigage method, check bearing clearances. Replace
bearings as necessary to obtain correct clearance. Bearings are
available in standard and undersize application.
2) If required, different sized upper and lower bearings may
be installed to obtain correct oil clearance. Tighten bolts to
specification. Check rod side play. Rotate crankshaft to ensure
freedom of movement. Reverse removal procedures for remaining
components. Tighten bolts to specification.
NOTE: Avoid combining bearing inserts in excess of .001" (.02 mm)
difference in size. Odd size inserts must be on bottom (rod
cap) side.
MAIN BEARINGS
Removal
1) Remove oil pan. See OIL PAN REMOVAL at end of ENGINE
section. Remove oil pump. See OIL PUMP under ENGINE OILING.
2) Ensure main bearing caps are marked for location. Rotate
crankshaft to remove bearings. Note color code on edge of bearing.
NOTE: Crankshaft journal diameters are indicated by a color coded
mark placed on the adjacent counterweight or cheek toward
the flanged (rear) end of crankshaft. Note color code to
determine proper bearing usage. Check oil clearance after
bearing installation.
Installation
1) Note color code on edge of bearings removed. Install
bearings. Ensure caps are installed in original location. Using
Plastigage method, check bearing clearances.
2) Replace bearings as necessary to obtain correct clearance.
Bearings are available in standard and undersize applications. If
required, different sized upper and lower bearings may be installed to
obtain correct oil clearance.
NOTE: If different sized bearings are used, the odd sized bearings
must all be uniform in location (upper or lower). DO NOT use
bearings with a thickness difference exceeding .001" (.02
mm).
3) Apply Loctite to corners of rear main bearing cap prior to
final installation. Tighten bolts to specification. Check crankshaft
end play. See CRANKSHAFT END PLAY. Rotate crankshaft to ensure freedom
of movement. Reverse removal procedures for remaining components.
Tighten bolts to specification.

Crankshaft End Play
1) Using dial indicator, check crankshaft end play. Inspect
crankshaft thrust surfaces or thrust bearing for wear if not within
specification. See ENGINE SPECIFICATIONS table.
2) Replace thrust bearing if required. When replacing thrust
bearing, pry crankshaft forward then reward prior to tightening main
bearing cap to specification. Recheck end play. Replace crankshaft if
not within specification.
REAR MAIN BEARING OIL SEAL
Removal
Remove transmission, clutch housing and flywheel or drive
plate. Using screwdriver, pry oil seal from housing. Avoid damage to
surrounding area.
NOTE: Shim must be used when installing old type oil seal Part No.
(324 1669) only. DO NOT use shim when installing new type
oil seal Part. No. (8933 004 143).
Installation
1) Position wing nut on Seal Installer (J-36306) until it
contacts the shaft nut. See Fig. 7. Install shim if old type seal Part
No. (324 1669) is used.
2) Lubricate inner and outer edges of seal. Install seal on
seal installer with seal dust shield toward the wing nut. Install seal
installer on crankshaft so pilot and dowel are positioned on the
crankshaft.
3) Thread the seal installer attaching screws into the
crankshaft and tighten. Rotate wing nut until it bottoms. This will
properly position the seal.
4) Remove seal installer. Ensure dust shield is not curled
under. Reverse removal procedures for remaining components.
Fig. 7: Installing Rear Main Bearing Oil Seal
WATER PUMP
Removal

sensor. With engine warm, resistance should be less than 1000 ohms.
2) Connect one ohmmeter lead to sensor connector terminal.
Connect other lead, in turn, to ECU harness connector terminals 32
and 14. Repair wiring harness if resistance is greater than 1 ohm.
COOLANT TEMPERATURE SENSOR
1) Disconnect wiring harness from CTS sensor. Test
resistance of sensor. If resistance is not 185-100,700 ohms (3400
ohms at 70
F; 1600 ohms at 100F), replace sensor. With engine warm,
resistance should be less than 1000 ohms.
2) Connect one ohmmeter lead to sensor connector terminal.
Connect other lead, in turn to ECU harness connector terminals 15 and
32. Repair wiring harness if an open circuit is indicated.
WIDE OPEN THROTTLE (WOT) SWITCH
1) Disconnect wiring harness from WOT switch. Connect
ohmmeter leads to switch terminals, and manually open and close the
switch. When switch is closed, resistance should be infinite. A low
resistance should be indicated at wide open position. Test switch
operation several times. Replace WOT switch if defective. Reconnect
wiring harness.
2) With ignition switch "ON", connect voltmeter between pin
6 and pin 7 (ground) of diagnostic connector D2. Voltage should be
zero with switch in wide open position and greater than 2 volts in
any other position.
3) If voltage is always zero, test for short circuit to
ground in wiring harness or switch. Check for open circuit between
pin 8 of ECU connector and the switch connector. Repair or replace
wiring harness as necessary.
4) If voltage is always greater than 2 volts, test for an
open wire or connector between the switch and ground. Repair as
required.
CLOSED THROTTLE SWITCH
NOTE: It is important that all testing be done with the idle speed
actuator (ISA) motor plunger in the fully extended position
(as it would be after a normal engine shut down). If it is
necessary to extend the motor plunger to test the switch, an
ISA motor failure can be suspected. Refer to ISA motor test.
1) With ignition on, connect voltmeter positive lead to pin
13 of diagnostic connector D2. Attach negative lead to pin 7. Voltage
should be close to zero at closed throttle and greater than 2 volts
at any position other than closed throttle.
2) If the voltage is always zero, test for a short circuit
to ground in the wiring harness or switch. Test for an open circuit
between pin 25 of ECU connector and throttle switch.
3) If voltage is always more than 2 volts, test for an open
circuit in the wiring harness between the ECU and switch connector.
Also check for open circuit between the switch connector and ground.
Repair or replace wiring harness as needed.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
1) Inspect MAP sensor vacuum hose connections at sensor and
throttle body. Repair as required. Test MAP sensor output voltage at
MAP sensor connector pin B (as marked on sensor body) with the
ignition switch "ON" and engine off. See Fig. 15. Output voltage
should be 4.0-5.0 volts.

NOTE: Voltage should drop 0.5-1.5 volts with hot engine, at idle.
Fig. 6: MAP Sensor Terminal Identification
If markings on MAP sensor vary from illustration, use markings on
sensor.
2) Test voltage at pin 33 of ECU connector for 4.0-5.0 volts
to verify wiring harness condition. Repair if required.
3) With ignition on, check for MAP sensor supply voltage of
4.5-5.5 volts at sensor connector pin C. Similar voltage should be
present at pin 16 of ECU connector. Repair or replace wiring harness
if required. Test for sensor ground between pin 17 of ECU connector
and pin A of sensor connector.
4) Using an ohmmeter, check for ground from pin 17 of ECU
connector to pin 2. If an open circuit is indicated, check for a
defective sensor ground on the flywheel housing near the starter
motor.
5) If ground is good, the ECU must be replaced. Before
replacing ECU, check to see if pin 17 of ECU connector is shorted to
12 volts. If so, correct the condition and test ECU before replacing.
Refer to the ELECTRONIC CONTROL UNIT TEST.
ELECTRONIC CONTROL UNIT

1) If all components have been checked and/or repaired, but
a system failure or problem still exists, the ECU may be at fault.
However, the ECU is a very reliable unit and must always be the final
component replaced if a doubt exists concerning the cause of a system
failure.
2) The only way to confirm an ECU malfunction is to take the
unit to an AMC dealer to have it tested. This is the only sure way to
avoid replacing a good ECU.
SYSTEM DIAGNOSIS
PRELIMINARY CHECKS
Be sure fuel is actually reaching the injector. Make sure no
air is entering the intake or exhaust system above the catalytic
converter. Before assuming an engine control system malfunction,
inspect the following systems to ensure components are in good
condition and are operating properly.
* All support systems and wiring.
* Battery connections and specific gravity.
* Electrical and vacuum connections on components and sensors.
* Emission control devices.
* Ignition system.
* Vacuum hoses.
CAUTION: Never connect or disconnect a component without turning the
ignition switch off. Never apply more than 12 volts or AC
voltage to system terminals. Disconnect battery cables
before charging it. Remove ECU if temperatures are expected
to exceed 176
F (80C), such as in a paint shop bake oven.
DIAGNOSTIC TEST CHARTS
Following are 6 different diagnostic test flow charts,
providing the shortest means of testing the system. These include:
* Ignition Switch "OFF" Chart - Tests system power for ECU
memory keep-alive voltage.
* Ignition Switch "ON" Power Chart - Tests system power
function and fuel pump power function.
* Ignition Switch "ON" Input Chart - Tests closed throttle
(idle) switch, wide open throttle (WOT) switch, manifold
absolute pressure (MAP) sensor, park/neutral switch, coolant
temperature sensor (CTS), manifold air/fuel temperature (MAT\
)
sensor and the respective switch or sensor circuits.
* System Operational Chart - Tests engine start-up and fuel
injector circuits, plus function of closed loop air/fuel
mixture, coolant temperature sensor, manifold air/fuel
temperature sensor, knock sensor and closed loop ignition
retard/advance, EGR valve and canister purge solenoid, idle
speed actuator, and A/C control.
* Basic Engine Chart - Indicates possible failures within other
engine related components.
* Man. Trans. Up-shift Chart - Tests up-shift indicator lamp
function on manual transmission vehicles.