engine JEEP CHEROKEE 1988 Service Repair Manual

Spark control systems are designed to ensure the air/fuel
mixture is ignited at the best possible moment to provide optimum
efficiency and power and cleaner emissions.
Ensure vacuum hoses to the distributor, carburetor, spark
delay valves, thermal vacuum switches, etc., are in place and routed
properly. On Computerized Engine Controls (CEC), check for presence of\
required sensors (O2, MAP, CTS, TPS, etc.). Ensure they have not been
tampered with or modified.
Check for visible modification or replacement of the feedback
carburetor, fuel injection unit or injector(s) with a non-feedback
carburetor or fuel injection system. Check for modified emission-
related components unacceptable for use on pollution-controlled
vehicles.
AIR INJECTION SYSTEM (AIS)
Air Pump Injection System (AP)
The air pump is a belt-driven vane type pump, mounted to
engine in combination with other accessories. The air pump itself
consists of the pump housing, an inner air cavity, a rotor and a vane
assembly. As the vanes turn in the housing, filtered air is drawn in
through the intake port and pushed out through the exhaust port. See
Fig. 13 .
Check for missing or disconnected belt, check valve(s),
diverter valve(s), air distribution manifolds, etc. Check air
injection system for proper hose routing.
Fig. 13: Typical Air Pump Injection System
Courtesy of General Motors Corp.
Pulsed Secondary Air Injection (PAIR) System
PAIR eliminates the need for an air pump and most of the
associated hardware. Most systems consists of air delivery pipe(s),
pulse valve(s) and check valve(s). The check valve prevents exhaust
gases from entering the air injection system. See Fig. 14.
Ensure required check valve(s), diverter valve(s), air
distribution manifolds, etc., are present. Check air injection system
for proper hose routing.

Fig. 14: Typical Pulsed Secondary Air Injection System
Courtesy of General Motors Corp.
OXYGEN SENSOR (O2)
The O2 sensor is mounted in the exhaust system where it
monitors oxygen content of exhaust gases. Some vehicles may use 2 O2
sensors. The O2 sensor produces a voltage signal which is proportional
to exhaust gas oxygen concentration (0-3%) compared to outside oxygen
(20-21%). This voltage signal is low (about .1 volt) when a lean
mixture is present and high (1.0 volt) when a rich mixture is present.\
As ECM compensates for a lean or rich condition, this voltage
signal constantly fluctuates between high and low, crossing a
reference voltage supplied by the ECM on the O2 signal line. This is
referred to as cross counts. A problem in the O2 sensor circuit should
set a related trouble code.
COMPUTERIZED ENGINE CONTROLS (CEC)
The CEC system monitors and controls a variety of
engine/vehicle functions. The CEC system is primarily an emission
control system designed to maintain a 14.7:1 air/fuel ratio under most
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) emissions.
The CEC system consists of the following sub-systems:
Electronic Control Module (ECM), input devices (sensors and switches)\
and output signals.

EARLY FUEL EVAPORATION (EFE)
The EFE valve is actuated by either a vacuum actuator or a
bimetal spring (heat-riser type). The EFE valve is closed when engine
is cold. The closed valve restricts exhaust gas flow from the exhaust
manifold. This forces part of the exhaust gas to flow up through a
passage below the carburetor. As the exhaust gas quickly warms the
intake mixture, distribution is improved. This results in better cold
engine driveability, shorter choke periods and lower emissions.
Ensure EFE valve in exhaust manifold is not frozen or rusted
in a fixed position. On vacuum-actuated EFE system, check EFE thermal
vacuum valve and check valve(s). Also check for proper vacuum hose
routing. See Fig. 15.
Fig. 15: Typical Vacuum-Actuated EFE System
Courtesy of General Motors Corp.
EMISSION MAINTENANCE REMINDER LIGHT (EMR) (IF EQUIPPED)

If equipped, the EMR light (some models may use a reminder
flag) reminds vehicle operator that an emission system maintenance is
required. This indicator is activated after a predetermined
time/mileage.
When performing a smog check inspection, ensure EMR indicator
is not activated. On models using an EMR light, light should glow when
ignition switch is turned to ON position and should turn off when
engine is running.
If an EMR flag is present or an EMR light stays on with
engine running, fail vehicle and service or replace applicable
emission-related components. To reset an EMR indicator, refer to
appropriate MAINTENANCE REMINDER LIGHTS in the MAINTENANCE section.
MALFUNCTION INDICATOR LIGHT (MIL)
The Malfunction Indicator Light (MIL) is used to alert
vehicle operator that the computerized engine control system has
detected a malfunction (when it stays on all the time with engine
running). On some models, the MIL may also be used to display trouble
codes.
As a bulb and system check, malfunction indicator light will
glow when ignition switch is turned to ON position and engine is not
running. When engine is started, light should go out.

\003
EM IS SIO NS R EC ALL # 617 - O XYG EN S EN SO R & C AT. C O NV.

1 988 J e ep C hero ke e
EMISSION RECALL BULLETIN
EMISSIONS RECALL #617 - OXYGEN SENSOR AND CATALYTIC CONVERTER
Model(s): 1989 and 1990 Jeep Cherokee (XJ), Comanche (MJ) and\
Wrangler (YJ) Vehicles Equipped With a 2.5L Engine and
a Federal Emission Control System and Built After
November 27, 1988
Bulletin No.: 617
Date: May, 1995
NOTE: This is an Emission Recall bulletin.
VEHICLES AFFECTED
1989 and 1990 Jeep Cherokee (XJ), Comanche (MJ) and Wrangler (YJ)\
Vehicles Equipped With a 2.5L Engine and a Federal Emission Control
System and Built After November 27, 1988.
SERVICE INFORMATION
Failure of the oxygen sensor and catalytic converter on the listed
models, may cause a vehicle to be in violation of U.S Environmental
Protection Agency (EPA) Emissions Standards. To correct this
condition, the oxygen sensor and catalytic converter must be replaced
with improved design parts.
Details of this service action are explained in the following
sections.
SERVICE PROCEDURE VIDEOTAPE
No videotape of the service procedure for this recall will be
provided.
DEALER NOTIFICATION & VEHICLE LIST
INVOLVED DEALERS
Each dealer to whom involved vehicles were invoiced (or the current
dealer at the same street address) will receive a copy of this dealer
recall notification letter and a list of the involved vehicles by
first class mail.
The Vehicle List is arranged in Vehicle Identification Number (VIN)
sequence. Owners known to Chrysler are also listed. The lists are for
dealer reference in arranging for service of involved vehicles as
necessary.
ALL OTHER DEALERS
Each Jeep & Eagle dealer who does not receive a Vehicle List will
receive a copy of this dealer recall notification letter by first
class mail.
DIAL SYSTEM FUNCTION 70

Chrysler Corporation has determined that some 1989 and 1990 Jeep
Cherokee, Comanche and Wrangler vehicles equipped with a 2.5L engine,
may be in violation of Federal Emissions Standards.
The Problem is... The oxygen sensor and catalytic convener on your
vehicle (identified on the enclosed form), may be
susceptible to failure. This could result in
hydrocarbon (HC), carbon monoxide (CO) and oxides
of nitrogen (NOx) emission levels above the
allowable limits, which were established to protect
the public health from the dangers of air pollution.
What you must do... * Simply contact your Jeep dealer to schedule
a service appointment. Ask the dealer to hold
parts for your vehicle or order them prior to
your appointment.
* Bring the enclosed Owner Notification Form with
you to your dealer. It tells the dealer what
service is required for your vehicle.
What Chrysler and Chrysler will repair your vehicle free of charge
your dealer will do... (parts and labor). To do this, your dealer will
replace the oxygen sensor and catalytic
converter. The service will take about one hour
but additional time may be required depending on
how service work is scheduled and processed.
If you need help... If you have trouble getting your vehicle
repaired, please call the Chrysler Customer
Center, toll free, at 1-800-853-1403.
A representative will assist you in getting your
vehicle repaired. If you are still unable to
obtain the repair as described in this letter
within a reasonable time, you may also contact
the Manufacturers Operations Division of the
Environmental Protection Agency (6405J), 401 M
Street, S.W., Washington, D.C. 20460.
In order to ensure your full protection under the emission warranty
made applicable to your vehicle under Federal law, and your right to
participate in future recalls, it is recommended that you have your
vehicle serviced as soon as possible. Failure to do so could legally
be determined to be a lack of proper maintenance of your vehicle.
Further, without this repair your vehicle may fail a state or local
emission inspection test.
We're sorry for any inconvenience, but trust that you understand our
interest in clean air and your continuing satisfaction with our
product. Thanks for your attention to this important matter.
Customer Services Field Operations
Chrysler Corporation

EM IS SIO NS S TA N DAR DS

1988 J e ep C hero ke e
1988 EMISSION & TUNE-UP STANDARDS
MANUFACTURING STANDARDS
Federal and state governments have established air quality
standard during the past 20 years. Automobile manufacturers design
their vehicles to conform to standards where the vehicle will be sold
and operated. These standards cover carbon monoxide (CO), hydrocarbons\
(HC) and oxides of nitrogen (NOx).
Federal and California Standards which must be met by
manufacturers are specified in units easily measured in a testing
laboratory. Since 1970, these standards have been in "grams per mile".
This means no vehicle, whether 2-cylinder or V8, may emit more than a
set weight (in grams) of pollutants for each mile travelled. Since
large engines burn more fuel per mile than do small engines, they must
be "cleaner" per gallon burned if they are to meet these standards.
When manufacturers certify vehicle models prior to sale,
the vehicles are placed on a dynamometer and the exhaust gases are
collected in a bag. After the vehicle runs for a specified time, the
gases are analyzed and weighed. Engines and emission systems are
designed so the weight of emissions will be less than the specified
grams per mile standard.
Infra-red exhaust analyzers are commonly used in vehicle test
stations. The analyzer uses a test probe placed in the exhaust stream
to sample the exhaust gases, and measure the percentage of CO and the
parts per million of HC. These are not the same units used by the
manufacturer when the vehicle is certified. The NOx emissions cannot
be measured by an infra-red exhaust analyzer. Laboratory equipment
must be used to determine NOx emissions.
TUNE-UP STANDARDS
The technician must use the proper specifications when
adjusting the vehicle during a tune-up. The first few years of
emission-regulated vehicles were adjusted using an exhaust gas
analyzer which measured CO and HC.
In the past few years, manufacturers have produced much
cleaner running vehicles. The CO (percentage) and HC (ppm) have beco\
me
very low, especially when measured downstream of catalytic converter.
It has become difficult to measure the effect of fuel and ignition
adjustments.
One solution to this problem for vehicles using carburetors
requires the use of artificially-enriched propane adjustments. The
added propane increases or decreases engine RPM for evaluation of
carburetor rich/lean setting. This allows the technician to check
carburetor setting quickly and accurately.
As computer-controlled systems were developed, it became
possible for the vehicles to adjust the air/fuel ratio, ignition
timing and emission control device operation throughout the entire
driving range. These computer control systems use a variety of sensors
that provide the electronic control unit with information on vehicle
speed, altitude of vehicle operation and transmission gear position,
along with engine operating conditions.
Fuel delivery to achieve a lean air/fuel ratio is controlled
by the computer. The computer controls the on/off (duty cycle) time of\
the fuel injector(s) or carburetor mixture control solenoid to achieve\
leanest possible air/fuel ratio while maintaining good driveability.
Although most repair shops have exhaust gas analyzers,
computer-controlled vehicles normally do not have a CO and HC

specification for tuning. An abnormal exhaust gas reading on an
exhaust analyzer may be helpful in diagnosing a problem, but should
not be used as a basis for adjustments.
These procedures and specifications are supplied by the
manufacturer and may not list CO or HC specifications.
STATE TEST STANDARDS
Some states have established standards for allowable
pollutants for used vehicles. These standards are normally given in CO
(percentage) and HC (ppm). Vehicle tail-pipe emissions can be checke\
d
against the standard using an exhaust gas analyzer. Typical standards
for newer vehicles would be 0.5 percent CO and 200 ppm HC. If vehicle
emissions are below this standard, vehicle would pass emissions test.
These standards are used to determine if the vehicle is running
properly, not to be used for tuning or adjusting the engine. If the
vehicle will not pass emission test or is running poorly, use the
manufacturer's diagnostic procedures and specifications for repair.
Test standards may change each year and vary from state to
state, and even by county within each state. It is not possible to
provide an accurate and up-to-date list of emissions standards.
Emission standards can be obtained for your area by contacting your
local county or state office. Remember, the emission standards are
only for test purposes. The manufacturer's adjustment procedures and
specifications must be followed when repairing vehicles.

EN G IN E C O OLIN G F A N

1988 J e ep C hero ke e
1987-88 ENGINE COOLING
Thermostatically Controlled Electric Fans
Cherokee, Comanche, Wagoneer
DESCRIPTION & OPERATION
On Cherokee, Comanche and Wagoneer models with a 4.0L engine,
A/C and/or heavy duty cooling system, an auxiliary electric fan is
used. The auxiliary fan is controlled by a relay mounted on the left
inner fender panel. A radiator temperature switch attached to the
radiator outlet tank above the lower radiator hose senses engine
coolant temperature.
When coolant temperature is more than 190(0)F (88(0)C), t\
he
radiator coolant temperature switch closes allowing current from the
ignition switch to flow through the fan relay to ground activating the
relay. When relay is activated, battery voltage is supplied to the fan
causing it to operate. When coolant temperature is below 190(0)F
(88(0)C), the radiator coolant temperature switch opens preventing t\
he
relay from being grounded and electric cooling fan from being
energized.
When the A/C (if equipped) is turned on, the Electronic
Control Unit (ECU) grounds the A/C relay coil allowing current to flow\
through it. This activates the A/C relay which then supplies current
to the A/C clutch, fan diode assembly and cooling fan relay. The
cooling fan relay is activated and the fan operates. Whenever the A/C
is used, regardless of engine coolant temperature, the auxiliary
electric cooling fan operates.
TESTING
NOTE: For following tests, refer to fan relay connector terminal
identification and fan controls identification. See Figs. 1
and 2.
With Air Conditioning
1) If electric cooling fan does not work all the time, go to
step 3). If electric cooling fan is inoperative when A/C compressor
operates, start engine and turn A/C on. Disconnect fan relay
connector. Fan relay is located on left inner fender panel.
2) Using a voltmeter, check for voltage at fan relay
connector terminal No. 2. If voltmeter does not read battery voltage,
replace fan diode assembly.
3) Disconnect fan relay connector. Fan relay is located on
left inner fender panel. Using a jumper wire with an in-line 25-amp
fuse, supply battery voltage to fan relay connector terminal No. 4.
4) If fan operates, motor is okay. Go to next step. If fan
motor does not operate, check continuity between fan relay connector
terminal No. 4 and body ground connections. If continuity exists,
replace fan motor. If continuity does not exist, repair open and
retest.
5) Disconnect fan relay connector. Turn ignition switch to
the "RUN" position. Check continuity between fan relay connector
terminal No. 5 and body ground connections. If continuity does not
exist, repair open circuit. If continuity exists, go to next step.
6) Using a jumper wire with an in-line 25-amp fuse, jump
across fan relay connector terminals No. 1 and No. 4. If fan motor
operates, go to next step. If fan motor does not operate, repair fan

EN G IN E O IL P A N R EM OVA L

1988 J e ep C hero ke e
1988 ENGINES
Jeep - Engine Oil Pan Removal
Cherokee, Comanche, Wagoneer
Wrangler, Grand Wagoneer
NOTE: Only engine applications with special oil pan removal and
installation procedures are included in this article.
Illustrations of most manufacturer's oil pans and attaching
hardware are provided.
Fig. 1: View of Jeep 2.5L Oil Pan
Courtesy of Chrysler Motors.