1988 JEEP CHEROKEE sensor

housing with 2 shoulder bolts. Tighten the engine speed sensor
shoulder bolts.
2) Connect the engine speed sensor wire connector.
ELECTRONIC CONTROL UNIT (ECU)
Removal
NOTE: The ECU is located below the instrument panel, between
the steering column and the A/C-Heater housing. See
Fig. 22. Three screws mount the ECU to a bracket.
1) Disconnect the negative battery cable.
2) Remove the 3 ECU attaching screws. See Fig. 23.
3) Disconnect the ECU wiring harness connector.
4) Remove the ECU.
Fig. 22: Location of ECU
Courtesy of Chrysler Motors.

4) Install the distributor gear washer and distributor gear
onto the shaft.
5) Install the distributor gear retaining pin.
6) Install the distributor rotor.
7) Install the distributor as specified in DISTRIBUTOR under
REMOVAL & INSTALLATION above in this article.
TORQUE SPECIFICATIONS
TORQUE SPECIFICATIONS








\









\









\









\









\









\







Application Ft. Lbs. (N.m)
Coolant Temperature Sensor ....................... 21 (28)
Distributor Hold-Down Clamp Bolt .......... 9.5-14 (13-19)
Manifold Air Temperature Sensor .................. 21 (28)
INCH Lbs. (N.m)
Knock Sensor ..................................... 89 (10)









\









\









\









\









\









\







Electronic Spark Timing (EST) is used on most computer
controlled systems. The Electronic Control Module (ECM) monitors
information from various engine sensors, computes desired spark
timing, and signals distributor for correct timing change. The HEI
distributor with EST does not have centrifugal advance weights,
springs, or a vacuum advance unit. See Figs. 2 and 3.
HEI & EST WITH ELECTRONIC SPARK CONTROL (ESC)
All fuel injected vehicles are equipped with Electronic Spark
Control (ESC). ESC systems contain a knock sensor mounted in the
engine block. A Blue wire connects the sensor to the ESC module. If
the sensor detects knock, it sends a signal to the module which, in
turn, signals the ECM. The ECM sends a signal to the distributor to
retard spark timing.
Fig. 2: Typical HEI/EST Distributor, Integral coil system shown.
Courtesy of General Motors Corp.
OPERATION

The ECM monitors information concerning crankshaft position,
engine RPM, engine load, atmospheric conditions, engine temperature,
and transmission gear position. This information is used by the ECM to
compute desired spark timing which is relayed to the distributor,
enabling appropriate changes to be made to ignition timing. A back-up
spark advance system is incorporated to signal ignition module in the
event of ECM failure.
CAUTION: Although similar in appearance, components of HEI/EST and
HEI distributors are NOT interchangeable.
All Models With EST
The distributor module is connected to ECM by a 4-wire EST
connector which performs the following functions:
* Terminal "A" of the 4-wire connector is the reference ground
low. It is grounded in the distributor and ensures ground
circuit does not have a voltage drop. If circuit is open,
engine may experience poor performance.
* Terminal "B" of the 4-wire connector is the by-pass circuit.
At about 400 RPM, ECM applies 5 volts to this circuit to
switch spark timing control from module to ECM. An open or
grounded by-pass circuit will set a code 42 and the engine
will operate at base timing, plus a slight amount of advance
built into the module.
* Terminal "C" is the distributor reference High circuit. This
circuit provides the ECM with RPM and crankshaft position
information.
* Terminal "D" is the EST circuit, which triggers the module.
The ECM does not know what actual timing is, but does know
when it receives the reference signal. It will advance or
retard spark from that point. If base timing is set
incorrectly, engine spark curve will be incorrect.
SENSORS
On EST systems, the coolant temperature sensor signals ECM to
advance timing on a cold engine and return timing to programmed
advance curve as engine reaches normal operating temperature. If
engine overheats, spark is retarded to prevent detonation. During
light throttle operation, throttle position sensor input to ECM allows
for additional advance.
Spark advance is also governed by input from engine RPM and
Manifold Absolute Pressure (MAP) sensor. When MAP output voltage is
low (high vacuum), ECM gives less spark advance. More spark advance is\
given when MAP output voltage is high (low vacuum).
ELECTRONIC SPARK CONTROL (ESC) SYSTEM
All Fuel Injected Engines
The basic components of Electronic Spark Control (ESC) system\
are detonation (knock) sensor, HEI/EST distributor, ESC module and
ECM. When detonation (knock) occurs, sensor sends an electrical signal\
to ESC module. The ESC module then sends the signal voltage to the
ECM. When the ECM senses a voltage drop (to less than one volt) on the\
knock sensor signal line, spark timing will be retarded. The ECM will
retard spark timing until all signals from detonation sensor cease.
See Fig. 4 .

MAIN TE N AN CE R EM IN DER L IG HT R ESET P R O CED URES

1988 J e ep C hero ke e
1988-92 MAINTENANCE
Chrysler Motors Maintenance Reminder Lights
Jeep; Cherokee, Comanche, Wagoneer (1988-90), Wrangler
EMISSION MAINTENANCE INDICATOR LIGHT (1988-90)
Vehicles are equipped with an emission maintenance indicator
light on instrument cluster. This light will come on one time at 82,
500 miles to alert driver that emission service is required. At this
time, oxygen sensor and PCV valve must be replaced and all other
emission components should be inspected and serviced or replaced as
necessary.
Indicator timer is located under dash, near accelerator pedal
or to right of steering column. Timer cannot be reset. To turn off
light, timer must be replaced or disconnected. Since timer and sensor
are interdependent, if timer should fail prematurely, oxygen sensor
should be replaced at same time to preserve correct replacement
interval.
To replace timer on Cherokee, Comanche and Wagoneer models,
remove cruise control module (if equipped). Remove timer mounting
screws. Disconnect electrical connector. On Wrangler models, remove
timer mounting screws. Disconnect electrical connector. On all models,
install remaining components.
EMISSION MAINTENANCE INDICATOR LIGHT (1991-92)
Vehicles are equipped with an emission maintenance indicator
light on instrument cluster. This light will come on one time at 82,
500 miles to alert driver that emission service is required. At this
time, oxygen sensor must be replaced and all other emission components
should be inspected and serviced or replaced as necessary. Chrysler's
Diagnostic Readout Box (DRB-II) tester is required to reset the
emission maintenance indicator light.
Reset Procedure
Using DRB-II tester, access SELECT SYSTEMS. Select
appropriate engine. Select with or without A/C. Select FUEL &
IGNITION. Select ADJUSTMENTS. Select RESET EMR LIGHT. Reset EMR light.
When DRB-II is finished resetting light, DRB-II display will read EMR
LIGHT IS RESET.

\003
REC ALL 5 61 - 4 .0 L E N G . F E D . V EH IC LE S - O XYG EN S EN SO R

1988 J e ep C hero ke e
EMISSION RECALL BULLETIN
EMISSIONS RECALL #561 - OXYGEN SENSOR
Model(s): 1987-90 (XJ) Jeep Cherokee, Wagoneer
1987-90 (MJ) Jeep Comanche
Bulletin No.: 561
Date: October, 1993
NOTE: This is an Emission Recall bulletin.
VEHICLES AFFECTED
1987-90 Jeep Cherokee and Wagoneer (XJ); and Comanche (MJ) vehicle\
s
equipped with a 4.0L engine and located outside of California.
SERVICE INFORMATION
Failure of the oxygen sensor on the listed models, may cause a
vehicle to be in violation of Federal Emissions Standards. To correct
the condition, the oxygen sensor must be replaced with an improved
design sensor.
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.
ALL DEALERS
Each Jeep & Eagle dealer will receive a copy of this dealer recall
notification letter by first class mail.
DIAL SYSTEM FUNCTION 70
All involved vehicles will be entered to DIAL System Function 70 at
the time of recall implementation for dealer inquiry by VIN as needed.
PARTS INFORMATION

IMPORTANT: A quantity of parts will be distributed initially and
billed to all involved dealers. This quantity will cover a
portion of the total vehicles involved. Additional parts
will ba supplied as indicated in the Special Parts Supply
Message with this notification letter.
Each involved dealer, to whom vehicles in the recall were invoiced
(or the current dealer at the same street address), will receive
enough Oxygen Sensor Packages, Recall P/N C3905610, to service 25% of
those vehicles (minimum of 5 and maximum of 20 packages).
Each uninvolved dealer will receive 5 parts packages to service
vehicles upon request.
Each parts package contains the following components:
PARTS INFORMATION
PARTS INFORMATION TABLE







\









\








\
 
Description  Qty. 










\









\

\b







Oxygen Sensor  1 










\









\

\b







Instruction Sheet  1 











\









\







\f
OWNER NOTIFICATION & SERVICE SCHEDULING
All involved vehicle owners known to Chrysler are being notified of
the service requirement by first class mail. They are requested to
schedule appointments for the service with their dealers at the
earliest possible date. A copy of the
CUSTOMER NOTIFICATION LETTER is
in this bulletin.
Enclosed with each owner notification is an Owner Notification Form.
The involved vehicle and recall are identified on the form for owner
or dealer reference as needed.
SERVICE PROCEDURE
A. OXYGEN SENSOR INSPECTION
1. Raise Vehicle on a hoist and locate oxygen sensor in exhaust
manifold as shown in Fig. 1.
a. If the oxygen sensor has a metal stone shield around the sensor
body continue with Step B.
b. If the sensor does not have a stone shield, a new sensor has
already been installed and no further service is required.
WARNING: Exhaust manifold becomes very hot during engine operation.
Allow engine to cool before removing oxygen sensor.
1. Disconnect the oxygen sensor electrical connector.
2. Remove oxygen sensor using a crowfoot socket.
3. Clean exhaust manifold threads.

4. Install provided oxygen sensor (P/N C3905610). Tighten to
30 N.m (22 ft-lb).
5. Connect oxygen sensor connector.
6. Lower vehicle.
Fig. 1: Wire Connector & Oxygen Sensor - Location
CUSTOMER NOTIFICATION LETTER