1988 JEEP CHEROKEE Service Repair Manual

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.

MANIFOLD AIR TEMPERATURE (MAT) SENSOR
Removal
1) Disconnect the MAT sensor wire connector. See Fig. 18.
2) Remove the MAT from the intake manifold.
Fig. 18: Manifold Air Temperature (MAT) Sensor Connectors
Courtesy of Chrysler Motors.
Installation
1) Install the MAT sensor to the cylinder block. Tighten the
MAT sensor to 21 Ft. Lbs. (28 Nm).
2) Connect the MAT sensor wire connector.

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
Removal
1) Disconnect the MAP sensor wire connector. See Fig. 19.
2) Disconnect MAP sensor vacuum supply hose from MAP sensor.
3) Remove the MAP sensor attaching nuts. Remove MAP sensor
from the firewall.
Fig. 19: View of Manifold Absolute Pressure (MAP) Sensor
Mounting Nuts & Vacuum Supply Hose
Courtesy of Chrysler Motors.
Installation

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

WARNING: The knock sensor MUST be tightened to the EXACT torque
specified in order to ensure proper operation.
1) Install the knock sensor to the cylinder block. Tighten
the knock sensor to 89 INCH Lbs. (10 Nm).
2) Connect the knock sensor wire connector.
3) Lower vehicle.
ENGINE SPEED SENSOR
Removal
1) Remove engine speed sensor wire connector. See Fig. 21.
2) Remove the engine speed sensor-to-transmission housing
attaching bolts. Remove engine speed sensor from transmission housing.
Fig. 21: Engine Speed Sensor Mounting Bolts
Courtesy of Chrysler Motors.
Installation
1) Install the engine speed sensor to the transmission

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.

Fig. 23: Location of ECU Mounting Screws
Courtesy of Chrysler Motors.
Installation
1) Connect the ECU wiring harness connector.
2) While holding the ECU in position, attach the 3 ECU
attaching screws. See Fig. 23.
3 Connect the negative battery cable.
DISTRIBUTOR