1988 JEEP CHEROKEE Service Repair Manual

When handling an electronic part that is ESD sensitive, the
technician should follow these guidelines to reduce any possible
electrostatic charge build-up on the technician's body and the
electronic part.
1) Always touch a known good ground source before handling
the part. This should be repeated while handling the part and more
frequently after sitting down from a standing position, sliding across
the seat or walking a distance.
2) Avoid touching electrical terminals of the part, unless
instructed by a diagnostic procedure.
3) DO NOT open the package of a new part until it is time to
install the part.
4) Before removing the part from its package, ground the
package to a known good ground source.
CHECKING STATIC-SENSITIVE CIRCUITS/DEVICES
1) Solid State circuits in electronic devices are shown
greatly simplified in schematics. See Fig. 2. Due to the
simplification of the electronic devices on the schematic, resistance
measurements could be misleading or could lead to an electrostatic
discharge. Always follow the recommended diagnostic procedure.
Fig. 2: Sample Schematic Showing Typical ESD Sensitive Device
2) Only measure resistance at the terminals of the devices
when instructed by the recommended diagnostic procedure.
3) When using a voltmeter, be sure to connect the ground lead
first.

EM IS SIO N A PPLIC ATIO N

1988 J e ep C hero ke e
1988 ENGINE EMISSIONS
Jeep Emission Control Applications
Cherokee, Comanche, Grand Wagoneer, Pickup,
Wagoneer, Wrangler
EMISSION CONTROL DEVICE APPLICATIONS
EMISSION CONTROL DEVICE APPLICATIONS TABLE








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2.5L (150") 4-Cyl. TBI
PCV, EVAP, OC (3), EGR, SPK, CEC, O2
4.0L (242") 6-Cyl. MPFI
PCV, EVAP, AIS (2), DBC, EGR, SPK, CEC, O2, ACV, ASV
4.2L (258") 6-Cyl. 2-Bbl.
PCV, TAC, AIS, EVAP, DBC, EGR, SPK, CEC, O2, ACV, ASV,
EFE, EGR-CTO, EGR-TVS, MCU, SLV, VSA (1)
5.9L (360") V8 2-Bbl.
PCV, TAC, AIS, EVAP, DBC, EGR, SPK, ACV, DLV, EGR-CTO,
EGR-TVS, MCU (2), NLV, RDV, VA-CTO (2) (3), VSA (2)
(1) - Some Fed., all Calif.
(2) - Calif. only.
(3) - TWC on Calif.









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ABBREVIATION DEFINITIONS
ABBREVIATIONS DEFINITIONS TABLE








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Abbreviation Description
ACV ......................................... Air Control Valve
AIS ...................................... Air Injection System
ASV ....................................... Air Switching Valve
CEC ............................... Computerized Engine Control
DC-VLV ..................................... Deceleration Valve
DLV ............................................... Delay Valve
DVTRV .......................................... Diverter Valve
EGR ................................. Exhaust Gas Recirculation
EGR-CTO ...................... EGR Coolant Temperature Override
EGR-FDLV ............................... EGR Foward Delay Valve
EGR-TVS ............................. EGR Thermal Vacuum Switch
EST .................................. Electronic Spark Control
EVAP ................................... Evap. Emission Control
HDSP-CT ............... Heavy Duty Spark Coolant Temp. Override
HDVA-CTO ....... Heavy Duty Vac. Advance Coolant Temp. Override
MCU ....................................... Micro Computer Unit
MPS .................................. Manifold Pressure Sensor
NLRV .............................. Non-Linear Vacuum Regulator
OC ......................................... Oxidation Catalyst
O2 .............................................. Oxygen Sensor
PCV ............................ Positive Crankcase Ventilation
RDV ....................................... Reverse Delay Valve
S-CTO ............................ Spark Coolant Temp. Override
SLV ................................................... Solevac

SPK ..................................................... Spark
TAC .................................. Thermostatic Air Cleaner
TPS .................................. Throttle Position Sensor
TSD ......................................... Throttle Solenoid
TP ........................................ Throttle Positioner
TWC ........................................ Three-Way Catalyst
VA-CTO .................. Vacuum Advance Coolant Temp. Override
VSA .................................... Vacuum Switch Assembly
VTP ................................ Vacuum Throttle Positioner









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EM IS SIO N C O M PO NEN T ID EN TIF IC ATIO N

1988 J e ep C hero ke e
1988 Exhaust Emission Systems
JEEP SYSTEMS
NOTE: Information not available from manufacturer for Jeep 2.5L
TBI and 4.0L MPFI emission systems.
DESCRIPTION
Several systems are used to control emissions. System usage
depends on model, engine and transmission combinations. Each system
is designed to control vehicle emissions. In addition, specially
calibrated carburetors (carbureted models), fuel injection system,
distributors and modified combustion chambers are used with these
systems.
AIR INJECTION
Air injection system consists of air pump, diverter valve,
check valve, and various air distribution lines necessary to inject
fresh air adjacent to exhaust valves. Injection of fresh air adjacent
to exhaust valves creates an afterburn which further consumes
unburned gases in engine's exhaust.
CATALYTIC CONVERTER (CAT)
Converter is installed in vehicle's exhaust system to aid in
reduction of exhaust emissions. This unit changes unburned
hydrocarbons (HC) and carbon monoxide (CO) into water vapor and
carbon dioxide.
COMPUTERIZED EMISSION CONTROL (CEC) SYSTEM
CEC system closely controls air/fuel ratio through a
feedback system from an oxygen sensor in exhaust system. Major
components of this system include exhaust gas oxygen sensor, vacuum
switches, temperature switches, Micro Computer Unit (MCU), fuel
injection system or computer controlled carburetor (carbureted
models) to maintain a constant air/fuel mixture. For additional
information, see appropriate article in COMPUTERIZED ENGINE CONTROL
section.
EVAPORATIVE EMISSION CONTROL
All models use closed tank (sealed) system, which returns
raw fuel vapors and routes them to intake manifold for burning.
Carbon canister stores vapors until engine draws them off for burning.
OTHER EMISSION SYSTEMS
For additional information on description, operation,
testing and adjusting other exhaust emission systems, refer to the
following articles in this section.

EM IS SIO N C O NTR O L V IS U AL IN SPEC TIO N P R O CED URES

1988 J e ep C hero ke e
1983-98 GENERAL INFORMATION
Emission Control Visual Inspection Procedures
All Models
* PLEASE READ THIS FIRST *
This article is provided for general information only. Not
all information applies to all makes and models. For more complete
information, see appropriate article(s) in the ENGINE PERFORMANCE
Section.
EMISSION CONTROL LABELS
The vehicle manufacturer's emission control label, also known
as the underhood tune-up label or Vehicle's Underhood Emission Control
System (VECI) label, is located in the engine compartment. Information\
regarding year model of vehicle, engine size, number of cylinders,
emission equipment or type, engine tune-up specifications, whether
vehicle was manufactured for sale in California or is a Federal
vehicle, vacuum hose routing schematic, etc., can be found on this
label. See Fig. 1.
In addition to the VECI label, some emission control
inspection and maintenance programs may require an additional label to
be affixed to the vehicle in special circumstances. For example, in
California, a Bureau Of Automotive Repair (BAR) engine label may be
affixed to the left door post. A BAR engine label is only used when
the vehicle has an engine change, approved modification or is a
Specially Constructed (SPCN) or an acceptable Gray market vehicle.
Check your state's emission control inspection and maintenance laws to
determine if a similar label is used.
Fig. 1: Typical Emission Control Label
Courtesy of General Motors Corp.
EMISSION CONTROL VISUAL INSPECTION
* PLEASE READ THIS FIRST *
NOTE: The following emission control visual inspection procedures
should be used as a guide only. When performing a visual
inspection, always follow your state's recommended

inspection procedures.
A visual inspection is made to determine if any required
emission control devices are missing, modified or disconnected.
Missing, modified or disconnected systems must be made fully
operational before a vehicle can be certified.
POSITIVE CRANKCASE VENTILATION (PCV)
PCV controls the flow of crankcase fumes into the intake
manifold while preventing gases and flames from traveling in the
opposite direction. PCV is either an open or closed system. See Fig. 2
.
Ensure PCV system is installed as required. Verify valve,
required hoses, connections, flame arresters, etc., are present,
routed properly and in serviceable condition.
Fig. 2: Typical Open & Closed Type PCV System
THERMOSTATIC AIR CLEANER (TAC)
The TAC supplies warm air to air intake during cold engine
operation. This system is active during cold engine warm-up only.
Under all other operating conditions, air cleaner function is the same
as any non-thermostatic unit.
Ensure required exhaust shroud, hot air duct, vacuum hoses
and air cleaner components are present and installed properly. See
Fig. 3 . Ensure any required thermostatic vacuum switches are in place
and vacuum hoses are installed and in serviceable condition. Also
ensure air cleaner lid is installed right side up. Check for oversized
air filter elements and for additional holes in the air cleaner
housing.

Fig. 3: Typical Thermostatic Air Cleaner System
FUEL EVAPORATIVE SYSTEM (EVAP)
The EVAP system allows for proper fuel system ventilation
while preventing fuel vapors from reaching the atmosphere. This means
that vapors must be caught and stored while the engine is off, which
is when most fuel evaporation occurs. When the engine is started,
these fuel vapors can be removed from storage and burned. In most
systems, storage is provided by an activated charcoal (or carbon)
canister. See Fig. 4. On a few early systems, charcoal canisters are
not used. Instead, fuel vapors are vented into the PCV system and
stored inside the crankcase.
The main components of a fuel evaporation system are a sealed
fuel tank, a liquid-vapor separator and vent lines to a vapor-storing
canister filled with activated charcoal. The filler cap is normally
not vented to the atmosphere, but is fitted with a valve to allow both
pressure and vacuum relief.
Although a few variations do exist between manufacturers,
basic operation is the same for all systems. Check for presence of
vapor storage canister or crankcase storage connections when required.
Ensure required hoses, solenoids, etc., are present and connected
properly. Check for proper type fuel tank cap. Check for any non-OEM
or auxiliary fuel tanks for compliance and the required number of
evaporation canisters.

Fig. 4: Typical Fuel Evaporative System
CATALYTIC CONVERTERS
Oxidation Catalyst (OC)
This type of converter is the most common. It may use pellets
or monolith medium, depending upon application. See Fig. 5. Platinum
and palladium (or platinum alone) are used as catalyst in this type of\
converter.
Visually check for presence of catalytic converter(s). Check
for external damage such as severe dents, removed or damaged heat
shields, etc. Also check for pellets or pieces of converter in the
tailpipe.
Fig. 5: Typical Oxidation Catalytic Converter (Pellet Type) Shown;
Typical Three-Way Catalytic Converter Is Similar
Courtesy of General Motors Corp.
Three-Way Catalyst (TWC)
This type of converter is nearly identical to a conventional