1988 JEEP CHEROKEE lock

mounted on throttle body and senses angle of throttle blade opening.
A voltage signal of up to 5 volts at wide open throttle is
produced by TPS. Voltage varies with throttle angle changes. This
signal is transmitted to ECU where it is used to adjust air/fuel
ratio during acceleration, deceleration, idle, and wide open throttle
conditions.
A dual TPS is used on models with automatic transmissions.
This dual TPS not only provides ECU with input voltages but also
supplies automatic transmission control unit with input signals
relative to throttle position.
Knock Sensor
Knock sensor (detonation sensor) is located on lower left
side of cylinder block just above oil pan. Knock sensor picks up
detonation vibration from engine and converts it to an electrical
signal for use by ECU.
ECU uses this information to determine when a change in
ignition timing is required. Knock sensor allows for engine operation
on either "premium" unleaded or "regular" unleaded fuel.
When knock occurs, ECU retards ignition timing in one or
more cylinders until detonation is eliminated.
Speed Sensor
Speed sensor is secured by special shouldered bolts to
flywheel/drive plate housing. Speed sensor is nonadjustable and
preset at factory. Speed sensor senses TDC and engine speed by
detecting flywheel teeth as they pass pick-up coil during engine
operation. See Fig. 2.
Flywheel has a large trigger tooth and notch located 12
small teeth before each TDC position. When a small tooth and notch
pass the magnetic core in sensor, concentration and collapse of the
magnetic field created induces a small voltage spike into sensor
pick-up coil windings. These small voltage spikes are sent to ECU,
allowing ECU to count the teeth as they pass sensor.
When a large tooth and notch pass magnetic core in sensor,
increased concentration and collapse of the magnetic field induces a
higher voltage spike than smaller teeth. Higher spike indicates to
ECU that a piston will soon be at TDC position, 12 teeth later.
Ignition timing for cylinder is either advanced or retarded by ECU
based upon "sensor input".
Fig. 2: Speed Sensor Operation
Courtesy of Chrysler Motors.
Engine Switches
Several switches provide operating information to ECU. These

3) Voltage should be 4.5-5.5 volts. Same voltage should also
be at terminal C-14 of ECU wire harness connector. Using Diagnostic
Tester (M.S. 1170), test MAP sensor ground circuit at terminal D-3
and terminal "A" of sensor connector.
4) Using an ohmmeter, test MAP sensor ground circuit at ECU
connector between terminal D-3 of ECU connector and terminal B-11
with an ohmmeter.
5) If ohmmeter or diagnostic tester indicates an open
circuit, inspect for a defective sensor ground connection, located on
right side of cylinder block. If ground connection is good, ECU may
need to be replaced.
Fig. 5: MAP Sensor Test Points
Courtesy of Chrysler Motors.
O2 Sensor Heating Element Test
Disconnect O2 sensor connector. Connect an ohmmeter to
terminals "A" and "B" only (marked on the connector) of O2 sensor
connector. Resistance should be between 5 and 7 ohms. Replace sensor
if ohmmeter indicates an infinity reading.
CTS Test

1) Disconnect wire harness connector from CTS sensor. Test
resistance of sensor with a high impedance digital ohmmeter.
Resistance should be less than 1000 ohms with engine warm. See
TEMPERATURE-TO-RESISTANCE VALUES table.
2) Test resistance of wire harness between ECU terminal D-3
and sensor connector terminal. Repeat test at terminal C-10 of ECU
and sensor connector terminal. Repair wire harness if an open circuit
is indicated.
MAT Sensor Test
1) Disconnect wire harness connector from MAT sensor. Test
resistance of sensor with a high impedance digital ohmmeter.
Resistance should be less than 1000 ohms with engine warm. Replace
sensor if resistance is not within specified range. See
TEMPERATURE-TO-RESISTANCE VALUES table.
2) Test resistance of wire harness between ECU wire harness
connector terminal D-3 and sensor connector terminal. Repeat test
with terminal C-8 at ECU and sensor connector terminal. Repair wire
harness if an open circuit or resistance is greater than one ohm is
indicated.
TPS Test
See THROTTLE POSITION SENSOR TEST PROCEDURE chart in this
article.
TEMPERATURE-TO-RESISTANCE VALUES (CTS & MAT SENSOR) TABLE
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F
C Ohms
(Approximate)
212 .......................... 100 ........................... 185
160 .......................... 70 ............................ 450
100 .......................... 38 ........................... 1600
70 ........................... 20 ........................... 3400
40 ............................ 4 ........................... 7500
20 ........................... -7 ......................... 13,500
0 ............................ -18 ........................ 25,000
-40 .......................... -40 ....................... 100,700
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Knock Sensor Test
1) Start engine until engine reaches normal operating
temperature. Connect Diagnostic Tester (M.S. 1700). Observe knock
value on tester. Using tip of screw driver, gently tap on cylinder
block next to knock sensor and observe knock sensor value on tester.
2) Knock sensor value should increase while tapping on
cylinder block. If knock sensor value does not increase while tapping
on cylinder block, check knock sensor for proper connection. If
connection is good, replace knock sensor.
Speed Sensor Test
Disconnect speed sensor connector from ignition control
module. Place an ohmmeter between terminals "A" and "B". (Marked on
connector) Reading should be 125-275 ohms with engine hot. Replace
sensor if readings are not within specifications.
Idle Speed Stepper (ISS) Motor
1) Set parking brake and block drive wheels. Route all
tester cables away from cooling fans, drive belts, pulleys and
exhaust system. Always allow engine speed to return to normal before
disconnecting testing tools.
2) With ignition off, disconnect ISS motor connector at

throttle body. Connect Exerciser Tool (Part No. 8980 002 646) into
ISS motor. See Fig. 6.
3) Connect Red clip to battery positive cable. Connect
Black clip to battery negative cable. Red light on exerciser tool
will illuminate when properly connected. Start engine.
NOTE: When switch on exerciser tool is in "High" or "Low"
position, light on exerciser tool will flash indicating
voltage pulses are being sent to ISS motor.
4) Move exerciser tool switch to "High" position. Engine
speed should increase. Move switch to "Low" position. Engine speed
should decrease. If engine speed increases or decreases while using
exerciser tool, ISS motor is functioning properly.
5) Disconnect exerciser tool and reconnect ISS motor
connector. If engine speed does not change, turn ignition off and
remove ISS motor from throttle body.
6) With ignition off, switch exerciser tool between "High"
and "Low" positions. Check movement of ISS motor pintle. Pintle
should move in and out. If pintle does not move, replace ISS motor.
7) Start engine and test new ISS motor for proper
operation. If pintle operates properly, check ISS motor bore in
throttle body for blockage and clean as necessary. Reinstall ISS
motor into throttle body.
Fig. 6: ISS Motor Test Connector
Courtesy of Chrysler Motors.
Fuel Injector Test

See FUEL INJECTOR TEST PROCEDURE chart in this article.
REMOVAL & INSTALLATION
COOLANT TEMPERATURE SENSOR (CTS)
Removal & Installation
Drain cooling system. Remove air cleaner assembly.
Disconnect CTS wire connector. Remove CTS from engine block. Install
replacement CTS and connect CTS wire connector. Install air cleaner
assembly. Fill cooling system.
OXYGEN SENSOR
Removal & Installation
Raise and support vehicle. Disconnect O2 sensor wire
connector. Remove O2 sensor from exhaust manifold. Install O2 sensor
and tighten to 30 ft. lbs. (41 N.m). Connect O2 sensor wire connector
and lower vehicle.
KNOCK SENSOR
Removal & Installation
Raise and support vehicle. Disconnect knock sensor wire
connector. Remove knock sensor from cylinder block. Install knock
sensor and connect knock sensor wire connector. Lower vehicle.
SPEED SENSOR
Removal & Installation
Disconnect speed sensor wire connector. Remove 2 speed
sensor retaining bolts at transmission housing. Install speed sensor
and connect speed sensor wire connector.
STARTER MOTOR RELAY
Removal & Installation
Disconnect negative battery cable. Identify, tag and
disconnect wiring to relay. Remove relay retaining screws and remove
relay from inner fender panel. Install replacement relay and connect
relay wires. Connect negative battery cable. Test relay operation.
MANIFOLD AIR/FUEL TEMPERATURE (MAT) SENSOR
Removal & Installation
Disconnect wire connector from MAT sensor. Remove MAT sensor
from intake manifold. To install, reverse removal procedure.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
Removal & Installation
Disconnect wire connector, vacuum hose, and retaining nuts
from MAP sensor. Remove sensor from firewall. To install, reverse
removal procedure.
FUEL INJECTOR
WARNING: Always relieve residual fuel pressure in fuel delivery
system before opening system. To prevent chance of personal
injury, cover fittings with shop towel while disconnecting
fittings.

FUEL PRESSURE REGULATOR
WARNING: Always relieve residual fuel pressure in fuel delivery
system before opening system. To prevent chance of personal
injury, cover fittings with shop towel while disconnecting
fittings.
Removal & Installation
Remove injector fuel rail assembly. Remove 2 pressure
regulator retaining screws. Remove regulator from fuel rail. To
install, reverse removal procedure. Adjust regulator after
installation.
IDLE SPEED STEPPER (ISS) MOTOR
Removal & Installation
1) Disconnect ISS motor connector. Remove ISS motor
retaining screws and ISS motor. To install, reverse removal
procedure. No idle speed adjustment is necessary. Idle speed is
controlled by the Electronic Control Unit (ECU).
THROTTLE POSITION SENSOR
Removal & Installation
Disconnect TPS wire connector. Bend retaining bolts lock
tabs and remove retaining bolts. Remove TPS from throttle plate
assembly. To install, reverse removal procedure. Adjust TPS after
installation. See ADJUSTMENTS in this article.
EGR VALVE
Removal & Installation
Disconnect vacuum hose from EGR valve. Remove bolts which
hold EGR valve to intake manifold. Remove valve and discard gasket.
Clean intake manifold gasket mating surface. To install valve,
reverse removal procedure. Always use new gasket. See Fig. 8.

2.5L TBI
1) Adjustment of fuel pressure is required after replacement
of pressure regulator. Remove air inlet from throttle body. Connect
tachometer to diagnostic connector terminals D1-1 and D1-3. Connect
fuel pressure gauge to fuel body pressure test fitting.
NOTE: Some TBI models do not have a pressure test fitting on
throttle body. Use Fitting (PN 8983 501 572) for this
purpose.
2) Start engine and accelerate to 2000 RPM. Turn adjustment
screw to obtain 14.5 psi (1.02 kg/cm
) fuel pressure. Location of
adjustment screw is on bottom of regulator. Install lead seal ball to
cover regulator adjustment screw after adjusting fuel pressure to
specification. Turn ignition off. Disconnect fuel pressure gauge.
Install cap on test fitting. Install air inlet.
NOTE: To increase fuel pressure, turn adjustment screw inward. To
decrease fuel pressure, turn adjustment screw outward.
4.0L MPFI
1) Remove cap from pressure test port in fuel rail. Connect
Fuel Pressure Gauge (J-37730-1) to pressure fitting. Start vehicle.
Pressure should be approximately 31 psi (2.7 kg/cm
) with vacuum
hose connected to pressure regulator.
2) Pressure should be 39 psi (2.74 kg/cm
) with vacuum
hose removed from regulator. If fuel pressure is not to
specifications, check for kinks or restricting bends in fuel supply
and return lines. Check fuel pump flow rate. Pump should deliver
minimum of 1.06 quarts (one liter) of fuel per minute with fuel
return line pinched off.
3) If flow is inadequate, check system for plugged fuel
filter or filter sock. Fuel pump flow rate can be checked by
connecting a hose to fuel test port on fuel rail and inserting other
end in clean container.
4) To operate fuel pump, install a jumper wire into
diagnostic connector terminals D1-5 and D1-6. Pinch off fuel return
line to ensure that no fuel returns to fuel tank. If fuel pressure is
still not to specifications and fuel flow is normal, replace
regulator.
REMOVAL & INSTALLATION
FUEL PUMP
Removal (2.5L TBI)
1) Disconnect battery cables. Ensure fuel level is less than
1/2 for this procedure. Remove fuel outlet and return hoses. Remove
sending unit wires. Remove sending unit retaining lock ring.
2) Remove sending unit/pump assembly with "O" ring seal.
Disconnect fuel hose from fuel pump. Disconnect wires from fuel pump.
Remove fuel pump from sending unit.
Installation
Clean seal contact are of fuel tank. Install new "O" ring
seal. Install a new filter on end of suction tube. Position sending
unit/pump assembly in tank. To complete installation, reverse removal
procedure. Start engine and check for leaks.
CAUTION: Fuel leaks can develop from over tightening sending
unit/pump during installation.

1 - 25 Amp
Rear Washer/Wiper.
2 - 15 Amp
Radio, Cigarette Lighter.
3 - 25 Amp
Blower Motor.
4 - 20 Amp
Turn Signal, Back-Up Lights, Rear Window Defogger Relay.
5 - 10 Amp
Dome Light, Courtesy Lights, Glove Box Light, Cargo Light,
Radio Memory, Power Mirrors, Teltak Connector.
6 - 15 Amp
Hazard Warning System, Stoplights.
7 - 10 Amp
Parking Lights, Headlight Warning Chime/Buzzer, Instrument
Panel Light Dimmer.
8 - 7.5 Amp
Gauges, Instrument Cluster, Seat Belt Warning, Headlight
Delay, Chime Module, Overhead Console.
9 - 5 Amp
Instrument Panel Illumination.
10 - 25 Amp
Rear Window Defogger.
11 - 30 Amp (Circuit Breaker)
Power Door Locks, Power Seats, Trailer Towing Wiring Harness.
12 - 10 Amp
ETR Radio, Power Antenna.
13 - Not Used (1984-87); 7.5 Amp (1988)
Transmission Control Unit.
14 - 25 Amp
Headlight Delay, Horns, Security Alarm.
15 - 5.5 Amp (Circuit Breaker)
Front Wiper.
16 - 30 Amp (Circuit Breaker)
Power Windows.
17 - 10 Amp
Clock, Security Alarm (Ign).
CAUTIONS & WARNINGS
REPLACING BLOWN FUSES
Before replacing a blown fuse, remove ignition key, turn off
all lights and accessories to avoid damaging the electrical system. Be
sure to use fuse with the correct indicated amperage rating. The use
of an incorrect amperage rating fuse may result in a dangerous