1988 JEEP CHEROKEE sensor

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.

Disconnect solenoid vacuum hoses. Disconnect solenoid wiring
connector. Remove solenoid retaining bolts and solenoid. To install
valve, reverse removal procedure.
ECU CONNECTOR PIN IDENTIFICATION 24-PIN CONNECTOR MPFI TABLE
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Terminal No. Wire Function
A1 .................................................. Injector No. 3
A2 .................................................. Injector No. 6
A3 .................................................. Injector No. 2
A4 .................................................. Injector No. 4
A5 ................................................. Fuel Pump Relay
A6 ........................................................ Not Used
A7 ............................................. Oxygen Sensor Relay
A8 ..................................................... Shift Light
A9 ..................................................... Latch Relay
A10 ............................................. EGR/Evap. Solenoid
A11 ....................................................... Not Used
A12 ...................................................... A/C Relay
B1 .................................................. Injector No. 1
B2 .................................................. Injector No. 5
B3 ........................................................... AIS A
B4 .......................................................... AIS A1
B5 ........................................................... AIS C
B6 .......................................................... AIS C1
B7 .................................................. Battery (Pos.)\
B8 ........................................................ Ignition
B9 ........................................................ Not Used
B10 ............................................... Latched B (Pos.)\
B11 ......................................................... Ground
B12 ......................................................... Ground
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Fig. 9: Multi-Point Injection ECU Connector
Courtesy of Chrysler Motors.
ECU CONNECTOR PIN IDENTIFICATION 32-PIN CONNECTOR MPFI TABLE
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Terminal No. Wire Function
C1 ............................................. Speed Sensor (Pos.)\
C2 ..................................................... A/C Request
C3 ........................................................... Start
C4 ...................................................... P/N Switch
C5 .................................................... Sync. (Neg.)\

C6 ...................................................... MAP Sensor
C7 ...................................................... TPS Sensor
C8 ................................................ Air Temp. Sensor
C9 ........................................................ Not Used
C10 ........................................... Coolant Temp. Sensor
C11 ............................................... Injection Supply
C12 ................................................. TX Serial Data
C13 ....................................................... Not Used
C14 ...................................... MAP Sensor Supply Voltage
C15 ............................................. TPS Supply Voltage
C16 ................................................... Sync. (Pos.)\
D1 ............................................. Speed Sensor (Neg.)\
D2 ...................................................... A/C Select
D3 ................................................... Sensor Ground
D4 ........................................................ Not Used
D5 ........................................................ Not Used
D6 ........................................................ Not Used
D7 ........................................................ Not Used
D8 ............................................. Knock Sensor Ground
D9 ............................................. Oxygen Sensor Input
D10 ................................................ Injector Supply
D11 ................................................. RX Serial Data
D12 ....................................................... Not Used
D13 .................................................... Spark/Dwell
D14 ....................................................... Not Used
D15 ....................................................... Not Used
D16 ................................................... Knock Sensor
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Fig. 10: Multi-Point Injection Diagnostic Connector
Courtesy of Chrysler Motors.

Fig. 12: Throttle Position Sensor Test Procedure Chart (M/T)

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FU EL IN JE C TIO N S YSTE M - T B I

1 988 J e ep C hero ke e
1988 Electronic Fuel Injection
JEEP/RENIX THROTTLE BODY INJECTION
2.5L Cherokee, Comanche, Wagoneer, Wrangler
DESCRIPTION
The Throttle Body Injection (TBI) system is a single
injector system that introduces fuel into throttle body from above
throttle plate. Fuel injector, located within throttle body, is
controlled by the Electronic Control Unit (ECU).
The ECU is a sealed microprocessor that receives input
signals from several sensors and other related engine components.
Based on these inputs, ECU generates output signals that control and
adjust air/fuel mixture and ignition timing as necessary for proper
engine performance.
ECU also controls engine idle speed, emission control
systems, upshift indicator light (manual transmission only), and A/C
compressor clutch.
OPERATION
ELECTRONIC CONTROL UNIT (ECU)
On Cherokee, Comanche and Wagoneer, ECU is located under
instrument panel, above accelerator pedal. On Wrangler, ECU is
located behind glove box. Input information from various engine
sensors to ECU is used to determine engine operating conditions and
needs. Battery voltage input is used to ensure that correct output
voltage is supplied by ECU during fluctuations in battery voltage.
FUEL INJECTOR
Fuel injector is mounted in throttle body so that fuel is
injected into incoming airflow. When injector solenoid is energized,
armature and plunger move upward against spring. Check ball above
injector nozzle moves off seat and opens small orifice at end of
injector.
Fuel supplied to injector is forced around ball and through
orifice, resulting in fine spray of fuel. Volume of fuel injected is
dependent only on length of time that injector is energized by ECU,
as fuel pressure is constant at injector. During cold engine starts,
extra fuel is supplied so richer mixture will aid in starting.
FUEL PRESSURE REGULATOR
Fuel pressure regulator is integral part of throttle body.
Pressure regulator has a spring chamber that is vented to same
pressure as tip of injector. Because differential pressure between
injector nozzle and spring chamber is same, only the length of time
that injector is energized controls volume of fuel injected.
Fuel pump delivers more fuel than is required by engine.
Excess fuel goes to fuel tank from pressure regulator via fuel return
hose. Fuel pressure regulator function is mechanical and ECU does not
control it.
FUEL PUMP

Electric roller type fuel pump is located in fuel tank.
Integral check valve is used to maintain pressure in fuel delivery
system after pump stops running. Fuel pump operation is controlled by
ECU through a fuel pump relay.
IDLE SPEED ACTUATOR (ISA) MOTOR
ISA motor acts as movable idle stop to change throttle stop
angle. Both engine idle speed and deceleration throttle stop angle
are set by ISA. ECU controls ISA motor by providing appropriate
voltage outputs to produce idle speed or throttle stop angle required
for engine operating condition.
OXYGEN (O2) SENSOR
Oxygen sensor is equipped with a heating element that keeps
sensor at proper operating temperature at all times. Oxygen sensor is
located in exhaust pipe.
Maintaining proper sensor temperature at all times, system
enters "Closed Loop" operation sooner and remains in "Closed Loop"
during periods of extended idle. Electrical feed to oxygen sensor is
through ignition switch.
The ECU receives sensor voltage signal which varies with
oxygen content in exhaust gas. Signal is used by ECU as reference for
setting air/fuel mixture ratio. ECU varies voltage to injector both
to compensate for battery voltage fluctuations and to change duration
of injector opening for control of air/fuel mixture.
MANIFOLD AIR/FUEL TEMPERATURE (MAT) SENSOR
MAT sensor provides a signal to ECU that changes depending
upon temperature of air/fuel mixture in intake manifold. During high
temperature conditions, ECU will compensate for changes in density of
air.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
MAP sensor measures absolute pressure in intake manifold.
Both mixture density and ambient barometric pressure are supplied to
ECU by MAP sensor. Sensor is mounted in middle of firewall in engine
compartment. Sensor receives manifold pressure information through
vacuum line from throttle body. See Fig. 1.
Fig. 1: Manifold Absolute Pressure (MAP) Sensor
Courtesy of Chrysler Motors.
COOLANT TEMPERATURE SENSOR (CTS)

Coolant temperature sensor is installed in intake manifold
water jacket to provide coolant temperature input signal for ECU.
During cold engine operation, ECU will make mixture richer, make up
for fuel condensation in cold intake manifold, increase idle speed
during warm-up period, increase ignition advance and keep EGR system
inoperative until engine warms up.
THROTTLE POSITION SENSOR (TPS)
Throttle position sensor provides ECU with input signal, up
to about 5 volts, to indicate throttle position. This allows ECU to
control air/fuel mixture according to throttle position. TPS is
mounted on throttle body assembly.
WIDE OPEN THROTTLE (WOT) SWITCH
WOT switch provides an input signal to ECU when engine is at
wide open throttle. The ECU enriches air/fuel mixture. The WOT switch
is located on the side of throttle body.
CLOSED THROTTLE (IDLE) SWITCH
Idle switch is integral with ISA motor and provides voltage
signal to ECU. ECU will signal ISA motor to change throttle stop
angle in response to engine operating conditions.
UPSHIFT INDICATOR LIGHT
On vehicles equipped with a manual transmission, ECU
controls upshift indicator light. Indicator light is normally
illuminated when ignition is turned on without engine running.
Indicator light is turned off when engine is started.
Indicator light will be illuminated during engine operation
in response to engine load and speed. If transmission is not shifted,
ECU will turn light off after 3 to 5 seconds. A switch located on
transmission prevents indicator light from being illuminated when
transmission is shifted to highest gear.
ENGINE SPEED SENSOR
Engine speed sensor is attached to bellhousing. It senses
and counts teeth on flywheel gear ring as they pass during engine
operation. Signal from speed sensor provides ECU with engine speed
and crankshaft angle. On flywheel gear ring, large trigger tooth and
notch is located 90 degrees before each TDC point. Each trigger tooth
is followed by 12 smaller teeth and notches before TDC point is
reached.
As each of 12 small teeth and notches pass magnetic core in
speed sensor, concentration and collapse of magnetic field induces
slight voltage (spike) in sensor pick-up coil winding. See Fig. 2.
Larger trigger teeth and notches induce higher voltage (spike) in
sensor pick-up coil winding. These voltage spikes enable ECU to count
teeth as they pass speed sensor.
Higher voltage spike (from larger tooth and notch) indicates
to ECU that piston will be at TDC position after 12 smaller voltage
spikes have been counted. ECU will then either advance or retard
ignition timing depending upon remaining sensor inputs.