1988 JEEP CHEROKEE check engine light

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.

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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

throttle body. Connect Exerciser Tool (Part No. 8980 002 646) into
ISS motor. See Fig. 6.
3) Connect Red clip to battery positive cable. Connect
Black clip to battery negative cable. Red light on exerciser tool
will illuminate when properly connected. Start engine.
NOTE: When switch on exerciser tool is in "High" or "Low"
position, light on exerciser tool will flash indicating
voltage pulses are being sent to ISS motor.
4) Move exerciser tool switch to "High" position. Engine
speed should increase. Move switch to "Low" position. Engine speed
should decrease. If engine speed increases or decreases while using
exerciser tool, ISS motor is functioning properly.
5) Disconnect exerciser tool and reconnect ISS motor
connector. If engine speed does not change, turn ignition off and
remove ISS motor from throttle body.
6) With ignition off, switch exerciser tool between "High"
and "Low" positions. Check movement of ISS motor pintle. Pintle
should move in and out. If pintle does not move, replace ISS motor.
7) Start engine and test new ISS motor for proper
operation. If pintle operates properly, check ISS motor bore in
throttle body for blockage and clean as necessary. Reinstall ISS
motor into throttle body.
Fig. 6: ISS Motor Test Connector
Courtesy of Chrysler Motors.
Fuel Injector Test

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FU EL IN JE C TIO N S YSTE M - T B I

1 988 J e ep C hero ke e
1988 Electronic Fuel Injection
JEEP/RENIX THROTTLE BODY INJECTION
2.5L Cherokee, Comanche, Wagoneer, Wrangler
DESCRIPTION
The Throttle Body Injection (TBI) system is a single
injector system that introduces fuel into throttle body from above
throttle plate. Fuel injector, located within throttle body, is
controlled by the Electronic Control Unit (ECU).
The ECU is a sealed microprocessor that receives input
signals from several sensors and other related engine components.
Based on these inputs, ECU generates output signals that control and
adjust air/fuel mixture and ignition timing as necessary for proper
engine performance.
ECU also controls engine idle speed, emission control
systems, upshift indicator light (manual transmission only), and A/C
compressor clutch.
OPERATION
ELECTRONIC CONTROL UNIT (ECU)
On Cherokee, Comanche and Wagoneer, ECU is located under
instrument panel, above accelerator pedal. On Wrangler, ECU is
located behind glove box. Input information from various engine
sensors to ECU is used to determine engine operating conditions and
needs. Battery voltage input is used to ensure that correct output
voltage is supplied by ECU during fluctuations in battery voltage.
FUEL INJECTOR
Fuel injector is mounted in throttle body so that fuel is
injected into incoming airflow. When injector solenoid is energized,
armature and plunger move upward against spring. Check ball above
injector nozzle moves off seat and opens small orifice at end of
injector.
Fuel supplied to injector is forced around ball and through
orifice, resulting in fine spray of fuel. Volume of fuel injected is
dependent only on length of time that injector is energized by ECU,
as fuel pressure is constant at injector. During cold engine starts,
extra fuel is supplied so richer mixture will aid in starting.
FUEL PRESSURE REGULATOR
Fuel pressure regulator is integral part of throttle body.
Pressure regulator has a spring chamber that is vented to same
pressure as tip of injector. Because differential pressure between
injector nozzle and spring chamber is same, only the length of time
that injector is energized controls volume of fuel injected.
Fuel pump delivers more fuel than is required by engine.
Excess fuel goes to fuel tank from pressure regulator via fuel return
hose. Fuel pressure regulator function is mechanical and ECU does not
control it.
FUEL PUMP

NOTE: When diagnosing fuel system problems using following
procedures, no specialized service equipment is needed.
Following diagnostic procedures are NOT applicable if
special tester M.S. 1700 is used.
Six different test flow charts are used to fully evaluate
fuel injection system:
TEST 1: IGNITION OFF
This test checks that system power provides for ECU memory
keep-alive voltage.
TEST 2: IGNITION ON: POWER
This test checks system power function and fuel pump power
function.
TEST 3 & 3A: IGNITION ON: INPUT
These tests check the following components and their
circuits: closed throttle (idle) switch, Throttle Position Sensor
(TPS), MAP sensor, A/T gear selector switch, Coolant Temperature
Sensor (CTS) and MAT sensor. Coolant temperature and MAT sensors are
tested in cold condition. This procedure also checks all interrelated
wiring circuits as well.
TEST 4 & TEST 4A: SYSTEM OPERATIONAL
These tests check engine start-up circuit, fuel injector,
"Closed Loop" air/fuel mixture function, coolant temperature sensor
function, MAT sensor function, detonation sensor "Closed Loop"
ignition retard/advance function, EGR valve and canister purge
solenoid function, idle speed control and A/C control functions.
TEST 5: BASIC ENGINE
This test indicates failures in related engine components
that are not part of fuel injection system.
TEST 6: MANUAL TRANSMISSION UPSHIFT
This test checks upshift indicator light function on vehicles
with manual transmissions.
Fig. 5: Jeep/Renix Fuel Injection ECU Connector
Courtesy of Chrysler Motors.
REMOVAL & INSTALLATION

Fig. 15. With a hot idle condition, the voltage reading should drop to
between 0.5-1.5 volts.
3) Test ECU terminal "C-6" for the same voltage as described
in step 2) to verify the wiring harness. Repair as necessary.
4) Test the MAP sensor supply voltage at the sensor connector
terminal "C" with the ignition ON. Voltage reading should be between
4.5-5.5 volts. Check that the voltage reading at terminal "C-14" is
also 4.5-5.5 volts.
5) Repair or replace the wire harness as necessary.
6) Test the MAP sensor ground circuit at the sensor connector
terminal "A" and ECU connector terminal "D-3". Repair the wire harness
as necessary.
7) Using an ohmmeter, test the MAP sensor ground circuit at
the ECU connector between terminal "D-3" and terminal "B-ll". If an
open circuit is indicated, check for a defective sensor ground
connection. The MAP sensor ground is located on the right side of the
engine block.
8) If, after performing step 7), the ground connection is
verified to be good, check for a short to 12 volts at terminal "D-3".
If a short is found, repair the short and then replace the ECU.
KNOCK SENSOR TEST
1) Connect Diagnostic Tester M.S. 1700 to the vehicle.
2) Go to "State Display" mode.
3) Start the engine and let idle.
4) Observe knock sensor value.
5) Using the tip of a screwdriver, lightly tap the cylinder
block near the sensor while observing the knock sensor value.
6) The knock sensor value should increase when the cylinder
block is tapped.
7) If the knock sensor value does not increase while tapping
on the cylinder block near the knock sensor, check for proper
connections to the knock sensor. If connections are good, replace
the knock sensor. Refer to REMOVAL & INSTALLATION in this article.
ENGINE SPEED SENSOR TEST
1) Disconnect the engine speed sensor connector from the
ignition control module.
2) place an ohmmeter between terminals "A" and "B" (marked on\
the connector). On a hot engine, the resistance reading should be
between 125-275 ohms.
3) Replace sensor if readings are not within specification.
Fig. 16: View of Engine Speed Sensor Connectors (At Sensor)
Courtesy of Chrysler Motors.

the ENGINE PERFORMANCE section.
Fuel filter should be drained whenever "WATER IN FUEL"
warning light glows. Diesel fuel can damage asphalt and
painted surfaces. Always place a drain pan under fuel filter
to collect contaminated fuel. See Fig. 2.
1) Stop vehicle and turn engine off. Attach a long piece
of tubing to drain cock outlet. Place end of drain hose into
drain pan. Open filter assembly vent valve (Black + shaped
knob) and drain cock.
2) Drain approximately 1/2 pint (.24 Liters) from fuel
filter. Close vent valve and drain cock. Start engine and
check for leaks. If "WATER IN FUEL" warning lamp comes on
again, remove water contaminated fuel from fuel lines and
fuel tank.
WARNING: DO NOT bleed fuel lines on hot engine, as high exhaust
temperatures could cause fire. Use care when bleeding fuel
lines, as fuel is under extreme pressure and could penetrate
skin, causing personal injury. Wear safety goggles and
protective clothing when bleeding fuel lines.
CAUTION: DO NOT drain fuel/water separator when engine is running or
hot. Allow engine to cool before draining. Verify that the
WATER IN FUEL light on instrument panel is OFF.
Fig. 3: Locking Crankshaft at TDC
Courtesy of American Motors/Jeep Corp.