1988 JEEP CHEROKEE check engine

NOTE: Whenever transmission or drivetrain service is performed
that affects the suspension alignment, for example,
removing the engine cradle, it is required that the
alignment be checked and corrected if necessary.
AUTOMATIC TRANSMISSION/TRANSAXLE ASSEMBLIES
AUTOMATIC TRANSMISSION/TRANSAXLE ASSEMBLY INSPECTION








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Condition Code Procedure
Any internal component
failure that requires
removal of the assembly
from the vehicle for
service. ( 1) ........... A ........... ( 2) Require repair or
replacement of the automatic
transmission/transaxle
assembly.
( 1) - It is Required that the torque converter and all other
failure related components be inspected for cause and
condition.
( 2) - For components not requiring removal of the assembly,
refer to the component listing in this document.









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DIFFERENTIAL AND FINAL DRIVE ASSEMBLIES
NOTE: Does not include half shafts.
DIFFERENTIAL AND FINAL DRIVE ASSEMBLY INSPECTION









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Condition Code Procedure
Any internal component
failure that requires
removal of the assembly
from the vehicle for
service. ( 1) ........... A ... Require repair or replacement
of the differential assembly.
( 1) - For components not requiring removal of the assembly,
refer to the component listing in this document.









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MANUAL TRANSMISSION/TRANSAXLE ASSEMBLIES
MANUAL TRANSMISSION/TRANSAXLE ASSEMBLY INSPECTION








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Condition Code Procedure
Any internal component
failure that requires
removal of the assembly
from the vehicle for
service. ( 1) ........... A ... Require repair or replacement
of the manual
transmission/transaxle
assembly.
( 1) - For components not requiring removal of the assembly,

EG R F U NCTIO N T E STIN G

1988 J e ep C hero ke e
1983-88 Exhaust Emission Systems
JEEP EXHAUST GAS RECIRCULATION
TESTING
EGR VALVE
Valve Opening Test
1) With engine at normal operating temperature and at idle,
rapidly open and close throttle. Open throttle sufficiently to obtain
at least 1500 RPM. Movement should be noticed in EGR diaphragm.
2) If diaphragm does not move, probable causes are: faulty
vacuum signal to EGR, defective EGR diaphragm or defective
backpressure sensor diaphragm (if equipped), or leaks in vacuum lines
or connections.
Valve Closing Test
1) With engine at normal operating temperature and at idle,
manually depress EGR valve diaphragm. RPM should immediately drop,
indicating that EGR valve is not leaking and had been properly
cutting off exhaust gas flow at idle.
2) If there is no change in RPM and engine is idling
properly, exhaust gases are not reaching combustion chamber. Check
for plugged passage between EGR valve and intake manifold.
3) If engine idles poorly and RPM is not greatly affected by
manually moving diaphragm up, EGR valve is not closing off exhaust
gas flow. Check for carbon between pintle, leaking EGR valve gasket
or bad EGR valve.
COOLANT TEMPERATURE OVERRIDE (CTO) SWITCH
NOTE: Engine coolant temperature must be below 100F (38C) to
perform this test.
1) Check vacuum lines for leaks and correct routing.
Disconnect vacuum line at backpressure sensor (if equipped) or at EGR
valve, and attach this line to vacuum gauge.
2) Operate engine at 1500 RPM. No vacuum should be indicated
on gauge. If vacuum is shown, replace CTO switch.
3) Idle engine until coolant temperature exceeds 100
F
(38C) on 4-cylinder engines, or 115F (46C) on 6-cylinder and V8
engines.
4) Raise engine speed to 1500 RPM. Ported vacuum should be
shown on gauge. If not, replace CTO switch.
DUMP VALVE
1) With engine at normal operating temperature, remove dump
valve vacuum hose from manifold and plug manifold connection.
2) Raise engine speed to 2000 RPM. Vacuum should be present
at exhaust ports on bottom of valve. If not, replace valve.
3) Reconnect vacuum hose to manifold and raise engine speed
to 2000 RPM. No vacuum should be felt at exhaust ports on bottom of
valve. If vacuum is present, replace valve.
THERMAL VACUUM SWITCH (TVS)
1) With the air cleaner temperature below 40F (-4C),
disconnect vacuum hoses from TVS and connect vacuum source to large

valve.
FORWARD DELAY VALVE
Forward delay valve is located between EGR CTO switch and EGR
valve. It modifies initial vacuum signal applied to EGR valve by
delaying full vacuum force.
TESTING
EGR VALVE
Valve Opening Test
1) With engine at normal operating temperature and at idle,
rapidly open and close throttle. Open throttle sufficiently to obtain
at least 1500 RPM. Movement should be noticed in EGR diaphragm.
2) If diaphragm does not move, probable causes are: faulty
vacuum signal to EGR, defective EGR diaphragm or defective
backpressure sensor diaphragm (if equipped), or leaks in vacuum lines
or connections.
Valve Closing Test
1) With engine at normal operating temperature and at idle,
manually depress EGR valve diaphragm. RPM should immediately drop,
indicating that EGR valve is not leaking and had been properly cutting
off exhaust gas flow at idle.
2) If there is no change in RPM and engine is idling
properly, exhaust gases are not reaching combustion chamber. Check for
plugged passage between EGR valve and intake manifold.
3) If engine idles poorly and RPM is not greatly affected by
manually moving diaphragm up, EGR valve is not closing off exhaust gas
flow. Check for carbon between pintle, leaking EGR valve gasket or bad
EGR valve.
COOLANT TEMPERATURE OVERRIDE (CTO) SWITCH
NOTE: Engine coolant temperature must be below 100F (38C) to
perform this test.
1) Check vacuum lines for leaks and correct routing.
Disconnect vacuum line at backpressure sensor (if equipped) or at EGR
valve, and attach this line to vacuum gauge.
2) Operate engine at 1500 RPM. No vacuum should be indicated
on gauge. If vacuum is shown, replace CTO switch.
3) Idle engine until coolant temperature exceeds 100
F (38C)
on 4-cylinder engines, or 115F (46C) on 6-cylinder and V8 engines.
4) Raise engine speed to 1500 RPM. Ported vacuum should be
shown on gauge. If not, replace CTO switch.
DUMP VALVE
1) With engine at normal operating temperature, remove dump
valve vacuum hose from manifold and plug manifold connection.
2) Raise engine speed to 2000 RPM. Vacuum should be present
at exhaust ports on bottom of valve. If not, replace valve.
3) Reconnect vacuum hose to manifold and raise engine speed
to 2000 RPM. No vacuum should be felt at exhaust ports on bottom of
valve. If vacuum is present, replace valve.
THERMAL VACUUM SWITCH (TVS)

Wire lead conductors
exposed ................ B .. Require repair or replacement.
Wire lead corroded ...... A .. Require repair or replacement.
Wire lead open .......... A .. Require repair or replacement.
Wire lead shorted ....... A .. Require repair or replacement.
(1) - Refer to manufacturer's diagnostic trouble code procedure
and require repair or replacement of affected
component(s).
( 2) - Determine cause and correct prior to repair or replacement
of part.
( 3) - Determine source of contamination, such as engine
coolant, fuel, metal particles, or water. Require
repair or replacement.
( 4) - Inoperative includes intermittent operation or out of OEM
specification. Some components may be serviceable; check
for accepted cleaning procedure.









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CRUISE CONTROL BRAKE SWITCHES
See SWITCHES.
CRUISE CONTROL CABLES
See CRUISE CONTROL LINKAGES AND CABLES .
CRUISE CONTROL CLUTCH SWITCHES
See SWITCHES.
CRUISE CONTROL LINKAGES AND CABLES
CRUISE CONTROL LINKAGE AND CABLE INSPECTION








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Condition Code Procedure
Attaching hardware
broken ................. A ... Require repair or replacement
of hardware.
Attaching hardware
missing ................ C .......... Require replacement of
hardware.
Attaching hardware not
functioning ............ A ... Require repair or replacement
of hardware.
Bent .................... A .. Require repair or replacement.
Binding ................. A .. Require repair or replacement.
Bracket bent, affecting
performance ............ A .. Require repair or replacement.
Bracket bent, not
affecting performance .. .. ........ No service suggested or
required.
Bracket broken, affecting
performance ............ A ............ Require replacement.
Bracket broken, not
affecting performance .. .. ........ No service suggested or
required.
Bracket corroded,
affecting performance .. A .. Require repair or replacement.
Bracket corroded, not
affecting performance .. 2 .. Suggest repair or replacement.

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.