1988 JEEP CHEROKEE lock

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 OIL SEAL
Removal
1) Remove oil pan. See OIL PAN REMOVAL in this section.
Remove rear main bearing cap. Note direction of seal lip installation.
Remove seal from bearing cap. Loosen all remaining main bearing cap
bolts.
2) Using a brass drift, tap upper seal around crankshaft
until seal protrudes enough to permit removal with pliers. Remove
seal.
Installation
1) Clean crankshaft seal surface. Coat seal-to-block contact
areas with liquid soap. Lightly coat all seal lips with engine oil.
See Fig. 7 . Install upper seal into block with lip facing toward front
of engine.
2) Apply Silicone sealer on both sides of lower seal tabs.
Ensure no sealer is applied on seal lip. Apply liquid soap on seal-to-
cap contact surfaces.
3) Install lower seal into bearing cap with lip facing toward
front of engine. Ensure seal is firmly seated in bearing cap. Apply
Silicone sealer to chamfered edges of bearing cap. See Fig. 7.
CAUTION: DO NOT apply Silicone sealer on cap-to-block contact
surfaces. Sealer should only be applied to chamfered edges
only.
4) Install rear main bearing cap. Tighten main bearing cap
bolts to specification.
Fig. 7: Installing Rear Main Bearing Oil Seal
Courtesy of Chrysler Motors.
WATER PUMP

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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.

ECU signal line and the other end connected to ground. As throttle
valve angle changes, a return voltage is sent back to the ECU through
the third wire. Output voltage to the ECU is about one volt when
throttle valve is at idle position, and about 5 volts when throttle
valve is at wide open throttle.
A dual TPS is used on automatic transmission equipped models.
The additional sensor provides throttle position information to the
transmission.
Knock Sensor
A knock sensor is mounted on the lower left side of block,
just above the oil pan. This sensor detects abnormal engine vibration
due to "detonation" and/or "pre-ignition". The knock sensor supplies
detonation information to the ECU. The ECU then alters ignition timing
as needed to maintain maximum timing under most operating conditions.
Park/Neutral (P/N) Switch
The P/N switch is mounted in automatic transmission equipped
vehicles. The switch indicates when the transmission is in Park or
Neutral.
Speed Sensor
The speed sensor is a nonadjustable sensor attached to the
flywheel/drive plate housing with special shoulder bolts. This sensor
provides Top Dead Center (TDC) and engine speed information to the ECU\
by counting the flywheel teeth as they pass during engine operation.
The flywheel has a large trigger tooth and notch located 12 small
teeth before each TDC position. See Fig. 2.
Fig. 2: Design of Speed Sensor
When a small tooth and notch pass the magnetic core of the
sensor, the concentration and collapse of the magnetic field created
induces a small voltage spike into the sensor pick-up coil windings.

proper increased enrichment for the next engine start. Idle speed is
nonadjustable.
EMISSION CONTROL
The ECU electrically controls Exhaust Gas Recirculation (EGR).\
An ECU-controlled solenoid valve is used to control EGR valve
function. This valve is located on the left inner fender panel and is
operated by the ECU in response to coolant temperature, throttle
position, and manifold pressure.
Under conditions of engine warm-up, engine idle, wide open
throttle, or rapid acceleration/deceleration, the solenoid valve is
energized, blocking vacuum to the EGR valve. At normal operating
temperatures with engine speed above idle, the solenoid valve is de-
energized, allowing normal EGR valve function.
NOTE: If the electrical connector is removed from the EGR solenoid,
EGR flow will be allowed at all times.
A/C CLUTCH CONTROL
The ECU controls the A/C compressor clutch to improve idle
quality. The A/C compressor clutch will be engaged or disengaged as
deemed necessary by the ECU through the A/C clutch relay.
SHIFT LIGHT CONTROL
The shift light system is used on all manual transmission
equipped vehicles. The ECU monitors coolant temperature, throttle
position, vehicle speed, and engine speed to control the shift light.
The ECU calculates what gear position the vehicle should be in and
uses this information to turn on the light. The light indicates the
best shift point to the driver for maximum fuel economy.
The light is tested when the ignition switch is turned on.
When the engine is started, the light should go out. A transmission-
mounted switch prevents the light from illuminating when the
transmission is shifted into high gear. The ECU turns the light off if
the shift to the next higher gear is not performed within 3-5 seconds
after light comes on.
DIAGNOSIS & TESTING
PRELIMINARY CHECKS
Before assuming that the ECU is faulty, the following systems
and components must be in good condition and operating properly:
* Air filter.
* All support systems and wiring.
* Battery connections and specific gravity.
* Compression pressure.
* Electrical and vacuum connections to components, sensors and
switches.
* Emission control devices.
* Ignition system.
* All vacuum and fuel line (hose) connections.
FUEL SYSTEM TEST
Fuel Pressure
1) Remove cap from pressure test port on fuel rail and

COMPONENT TESTING
Throttle Position Sensor
See THROTTLE POSITION SENSOR DIAGNOSTICS chart near the end
of this article. See Fig. 8.
Coolant Temperature Sensor (CTS) &
Manifold Air Temperature (MAT) Sensor
1) Disconnect the electrical connector from the sensor. Using
a high impedance, digital volt/ohmmeter, measure the resistance of the
sensor. If measured resistance is not as specified, replace sensor.
See the CTS & MAT SENSOR TEMPERATURE-TO-RESISTANCE VALUE table.
2) Test electrical harness resistance of both sensors by
testing between ECU harness connector "D-3" and sensor connector. Also
test between sensor connector and ECU harness connector "C-10" ("C-8"
on MAT sensor). Repair wire if open circuit is detected. Repair MAT
sensor wiring harness if resistance is greater than one ohm.
CTS & MAT SENSOR TEMPERATURE-TO-RESISTANCE VALUE









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F(C) Ohms
212 (100) .................................. 185
160 (71) ................................... 450
100 (38) .................................. 1600
70 (21) ................................... 3400
40 (4) .................................... 7500
20 (-7) ................................. 13,500
0 (-18) ................................. 25,000
-40 (-40) .............................. 100,700









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Manifold Absolute Pressure (MAP) Sensor
NOTE: Terminal identification letters are stamped on MAP sensor
body.
1) Disconnect electrical connector from sensor. With ignition
on and engine stopped, measure voltage output of sensor terminal "B".
See Fig. 4 . Ensure wiring harness is okay by also measuring voltage at
ECU terminal "C-t". Output voltage should be 4-6 volts at both points.
Repair or replace wiring harness as required.
2) With ignition on and engine stopped, measure supply
voltage of sensor terminal "C". See Fig. 4. Ensure wiring harness is
okay by also measuring voltage at ECU terminal "C-14". Supply voltage
should be 4.4-5.5 volts at both points. Repair or replace wiring
harness as required.
3) Using an ohmmeter, measure ground circuit resistance at
sensor terminal "A" and ECU connector terminal "D-3". Ensure wiring
harness is okay by also measuring resistance between ECU terminal "D-
3" and "B-11". If ohmmeter indicates an open circuit, check for
defective sensor ground connection at right side of cylinder block.
4) If ground connection is okay, replace ECU. If ECU terminal
"D-3" has short to 12-volts, repair wire before replacing ECU. Repair
or replace wiring harness as required.

ELECTRONIC CONTROL UNIT (ECU)
Removal & Installation
Information not available from manufacturer.
COOLANT TEMPERATURE SENSOR (CTS)
Removal & Installation
Drain cooling system. Remove air cleaner assembly. Disconnect
electrical connector and remove sensor from block. To install, reverse
removal procedure. Refill cooling system.
OXYGEN (O2) SENSOR
Removal & Installation
Raise and support vehicle. Disconnect electrical connector
from sensor. Remove sensor from exhaust manifold. Install and tighten
sensor to 35 ft. lbs. (47 N.m). Reconnect electrical connector. Lower
vehicle.
THROTTLE POSITION SENSOR (TPS)
Removal
Disconnect electrical connector from TPS. Bend lock tabs away
from retaining screws and remove screws. Remove TPS.
Installation
With throttle valve in normal closed position, install TPS.
Install TPS retaining screws. Perform OUTPUT CHECK.
NOTE: Throttle position sensor is nonadjustable. Only output
voltage can be monitored.
Output Check (Manual Transmission Only)
1) Connect negative lead of digital voltmeter to terminal "B"
and positive lead to terminal "A" of TPS connector. Do not disconnect
electrical connector. Insert leads through back of connector. It may
be necessary to remove throttle body from vehicle to gain access to
connector.
2) Turn ignition on, engine off. With throttle closed and
resting against idle stop, input voltage should be about 5 volts. Move
positive lead from terminal "B" to terminal "C" and read voltage
output. Output voltage should be about 0.8 volt with throttle closed
and resting against idle stop.
3) If voltage is not as specified, loosen lower retaining
screw and pivot sensor for large adjustments. Loosen upper retaining
screw and pivot sensor for small adjustments. Adjust sensor so output
voltage reading equals 16 percent of input voltage. If voltage
specifications cannot be obtained, replace sensor. Remove voltmeter.
Tighten screws and bend retaining tabs into position.
ALL OTHER SENSORS, SOLENOIDS & SWITCHES
Removal & Installation
Removal of sensors, switches, and solenoids is accomplished
by disconnecting the electrical and/or vacuum connectors and removing
or detaching the component. To install, reverse removal procedure.
TESTING
NOTE: Refer to Figs. 8-10 for Testing information.

AB BREVIA TIO NS

1988 J e ep C hero ke e
GENERAL INFORMATION
COMMONLY USED ABBREVIATION
"A" ABBREVIATION TABLE
"A" ABBREVIATION TABLE







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ABBREVIATION DEFINITION 










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A Amperes 

A/C Air Conditioning 

A/T Automatic Transmission/Transaxle 

AAP Auxiliary Accelerator Pump 

AB Air Bleed 

ABCV Air Bleed Control Valve 

ABDC After Bottom Dead Center 

ABRS Air Bag Restraint System 

ABS Anti-Lock Brake System 

AC Alternating Current 

ACC A/C Clutch Compressor 

ACCS A/C Cycling Switch 

ACCUM Accumulator 

ACCY Accessory 

ACT Air Charge Temperature Sensor 

ACV Thermactor Air Control Valve 

ADJ Adjust or Adjustable 

ADV Advance 

AFS Airflow Sensor 

AI Air Injection 

AIR or A.I.R. Air Injection Reactor 

AIS Air Injection System 

ALCL Assembly Line Communications Link 

ALDL Assembly Line Diagnostic Link 

ARC Automatic Ride Control 

ASCD Automatic Speed Control Device 

ASCS Air Suction Control Solenoid 

ASD Auto Shutdown 

ASDM Air Bag System Diagnostic Module 

ASV Air Suction Valve 

ATC Automatic Temperature Control 

ATDC After Top Dead Center 

ATF Automatic Transmission Fluid 

ATS Air Temperature Sensor 

AXOD Automatic Transaxle Overdrive 

Abs. Absolute 

Accy. Accessory 

Alt. Alternator or Altitude 

Amp. Ampere 

Assy. Assembly 

Auto. Automatic 

Aux. Auxiliary 

Avg. Average 











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"B" ABBREVIATION TABLE
"B" ABBREVIATION TABLE









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ABBREVIATION DEFINITION 










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B/P Backpressure 

BAC By-Pass Air Control 

BAP Barometric Absolute Pressure Sensor 

BARO Barometric 

BBDC Before Bottom Dead Center 

BCM Body Control Module 

BDC Bottom Dead Center 

BHP Brake Horsepower 

BLK Black 

BLU Blue 

BMAP Barometric & Manifold Absolute Pressure Sensor 

BOO Brake On-Off Switch 

BP Barometric Pressure sensor 

BPS Barometric Pressure Sensor 

BPT Backpressure Transducer 

BRN Brown 

BTDC Before Top Dead Center 

BTU British Thermal Unit 

BVSV Bimetallic Vacuum Switching Valve 

Baro. Barometric 

Batt. Battery 

Bbl. Barrel (Example: 4-Bbl.) 

Blst. Ballast 

Blwr. Blower 

Brkr. Breaker 











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"C" ABBREVIATION TABLE
"C" ABBREVIATION TABLE







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ABBREVIATION DEFINITION 










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C Celsius (Degrees) 

C(3) I Computer Controlled Coil Ignition 

C(4) Computer Controlled Catalytic Converter 

CANP Canister Purge solenoid 

CARB California Air Resources Board 

CAT Catalytic Converter 

CB Circuit Breaker 

CBD Closed Bowl Distributor 

CBVV Carburetor Bowl Vent Valve 

cc Cubic Centimeter 

CCC Computer Command Control 

CCD Computer Controlled Dwell 

CCM Central Control Module 

CCO Converter Clutch Override 

CCOT Cycling Clutch Orifice Tube 

CCW Counterclockwise 

CDI Capacitor Discharge Ignition 

CEC Computerized Engine Control 

CFI Central Fuel Injection 

CID Cubic Inch Displacement 

CID Cylinder Identification sensor 

CIS Continuous Injection System 

CIS-E Continuous Injection System-Electronic 

CKT Circuit 

CLR Clear 

CNG Compressed Natural Gas