1988 JEEP CHEROKEE coolant temperature

with a warm engine. See the COOLANT TEMPERATURE SENSOR (CTS)
RESISTANCE VALUES table below.
COOLANT TEMPERATURE SENSOR (CTS) RESISTANCE VALUES








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Degrees F  Degrees C  Resistance (Ohms) 
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-40  -40  100,700 
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0  -18  25,000 
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20  -7  13,500 
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40  4  7,500 
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70  20  3,400 
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100  38  1,600 
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160  70  450 
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212  100  185 










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3) If any resistance is not within the range as specified in
the table, replace the coolant temperature sensor.
4) Test the resistance of the wire harness between the ECU
wire harness connector terminal "D-3" and the sensor connector
terminal "C-10".
5) Repair any open circuits.

MANIFOLD AIR TEMPERATURE (MAT) SENSOR TEST
1) Disconnect the MAT wire harness connector from the MAT
sensor. See Fig. 14*.
Fig. 14: Location of Manifold Air Temperature (MAT) Sensor
Courtesy of Chrysler Motors.
2) Using a high input impedance (digital) volt-ohmmeter, tes\
t
the resistance of the sensor. Resistance should be less than l000 ohms

SPARK PLUG CHECK
Faulty or fouled plugs may perform well at idle speed, but at
higher engine speeds, they frequently fail. Faulty plug can exhibit
the following symptoms:
* Poor fuel economy.
* Power loss.
* Decreased engine speed.
* Hard starting.
* Generally poor performance.
Spark plugs also malfunction due to carbon fouling,
excessive electrode air gap, or broken insulators.
SYNC PULSE SIGNAL GENERATOR (STATOR) TEST
NOTE: For this test, an analog voltmeter MUST be used.
1) Insert the positive (+) lead of the voltmeter into the
Blue wire at the distributor connector.
2) Insert the negative (-) voltmeter lead into the Gray/Whit\
e
wire at the distributor connector.
CAUTION: DO NOT remove the distributor connector from distributor.
Insert the voltmeter leads into the backside of the
distributor connector to make contact with the terminals.
3) Set the voltmeter to the 15-Volt D/C scale. Turn ignition
key to "ON".
4) The voltmeter should display approximately 5.0 volts.
5) If no voltage displays, check that the voltmeter leads are
making good contact. If there is still no voltage, go to next step.
6) Remove the ECU and check for voltage at pin "C-16" and
ground with harness connected. If there in still no voltage, proceed
to the next step.
7) Connect Diagnostic Tester M.S. 1700 to the vehicle. Using
the diagnostic tester, perform vehicle test. If voltage is present, go
to the next step.
8) Check for continuity between the Blue wire at the
distributor connector and pin C-16 at the ECU.
9) If there in no continuity, repair harness as necessary.
10) Check for continuity between the Gray/White wire at the
distributor connector and pin C-5 at the ECU.
11) If there is no continuity, repair harness as necessary.
12) Check for continuity between the Black wire at the
distributor connector and ground.
13) If there is no continuity, repair harness as necessary.
14) While observing the voltmeter, crank the engine; the
voltmeter needle should fluctuate back and forth while the engine in
cranking. A fluctuation verifies that the stator in the distributor is
operating properly.
15) If there is no pulse sync, replace the stator. Refer to
REMOVAL & INSTALLATION below in this article.
REMOVAL & INSTALLATION
COOLANT TEMPERATURE SENSOR (CTS)
Removal
1) Drain the cooling system.

2) Remove air cleaner assembly.
3) Disconnect the CTS wire connector. See Fig. 17.
4) Remove the CTS from the left side of the engine block.
Fig. 17: Coolant Temperature Sensor (CTS) Connector
Courtesy of Chrysler Motors.
Installation
1) Install the CTS to the cylinder block. Tighten the CTS
to 21 Ft. Lbs. (28 Nm).
2) Connect the CTS wire connector.
3) Install air cleaner assembly.
4) Fill the cooling system.

1) Install the MAP sensor to the firewall. Tighten the MAP
sensor attaching nuts.
2) Connect the MAP sensor vacuum supply hose.
3) Connect the MAP sensor wire connector.
KNOCK SENSOR
Removal
1) Raise and support the vehicle.
2) Disconnect the knock sensor wire connector located below
and to the rear of the Coolant Temperature Sensor. See Fig. 20.
3) Remove knock sensor from left side of the engine block.
Fig. 20: Knock Sensor Connector
Courtesy of Chrysler Motors.
Installation

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








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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)









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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 .

\003
IN STR UM EN T P A N EL - S TA N DAR D

1988 J e ep C hero ke e
1988 Switches & Instrument Panels
JEEP
DESCRIPTION & OPERATION
Instrument panel is composed of speedometer housing,
tachometer and instrument cluster gauges.
FUEL GAUGE
System consists of a fuel gauge, an in-tank sending unit, and
appropriate wiring. Fuel gauge is grounded through variable resistor
of sending unit. A float attached to a slide rheostat follows fuel
level and varying resistance increases or decreases indicator reading.
TEMPERATURE GAUGE
System consists of gauge and sending unit and appropriate
wiring. The gauge is grounded through variable resistor of sending
unit. Changes in coolant temperature vary resistance in sending unit,
increasing or decreasing indication on gauge.
VOLTMETER
The voltmeter indicates regulated voltage to provide an
indication of charging system's ability to maintain battery charge.
OIL PRESSURE GAUGE
The oil pressure gauge system consists of gauge and a
variable resistance sending unit. Gauge needle, attached to bi-
metallic strip, responds to temperature changes.
REMOVAL & INSTALLATION
INSTRUMENT CLUSTER
Removal & Installation
1) Disconnect negative battery cable. On models with cruise
control, reach behind instrument cluster and disconnect speedometer
cable from speed switch. See Fig. 1.
2) On models without cruise control, raise vehicle on hoist.
Disconnect speedometer cable from transfer case (or transmission) and
at frame rail bracket. Move speedometer cable forward and upward to
provide slack. Lower vehicle.
3) On all models, remove instrument panel bezel screws and
bezel. Remove screws attaching cigarette lighter and switch housings
to instrument panel. Move housings aside.
4) Remove screws attaching cluster to instrument panel and
carefully pull cluster and speedometer toward rear of vehicle.
Disconnect wiring harness connectors.
5) Squeeze speedometer cable locking tabs and disconnect
cable from speedometer. See Fig. 1. Remove instrument cluster. To
install, reverse removal procedure.

Fig. 10: Identification Label Locations
Courtesy of American Motors Corp.
LUBRICATION SPECIFICATIONS
LUBRICATION SPECIFICATIONS TABLE








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Application Fluid Specifications
Automatic Transmission ......................... Dexron-IIE ATF
Brake Master Cylinder ......... DOT 3 (SAE J-1703F) Brake Fluid
Engine Coolant .......... Alugard 340-2 & Water (50/50 Mixture)
Engine Oil ( 1)
Gasoline Engine
Temperature Range
Above 30
\b F (-1\bC) ....... SAE 20W-40 Or 20W-50 API SH/CD
Above 0\b F (-18\bC) ........ SAE 10W-30 Or 10W-40 API SH/CD
Less Than 60\b F (16\bC) .............. SAE 5W-30 API SH/CD
Diesel Engine
Temperature Range
Above 30
\b F (-1\bC) ................ SAE 15W-40, 20W-40 Or
20W-50 API SH/CD
0
\b F (-18\bC) to 100\b F (38\bC) ...... SAE 10W-30 API SH/CD
Less Than 50\b F (10\bC) .............. SAE 5W-30 API SH/CD
Front Axle ................................ SAE 80W-90 API GL-5
Rear Axle ................................. SAE 80W-90 API GL-5
Rear Axle (Trac-Lok) ( 2) ................. SAE 80W-140 API GL-5
Rear Axle (Trailer Towing) ( 3) .......... SAE 75W-140 Synthetic
Hydraulic Clutch .............. DOT 3 (SAE J-1703F) Brake Fluid
Manual Transmission ....................... SAE 75W-90 API GL-5
Manual Steering Box .............. Multi-Purpose NLGI Grade 2EP
Power Steering Pump ...................... Power Steering Fluid
Transfer Case .................................. Dexron-IIE ATF