1988 JEEP CHEROKEE Service Repair Manual

Fig. 8: EGR Valve
Courtesy of Chrysler Motors.
EGR SOLENOID

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. 11: Comanche Multi-Point Fuel Injection Wiring Diagram
(Wiring Diagram Not Available for Cherokee & Wagoneer Models)

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

Fig. 13: Fuel Injector Test Procedure Chart

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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)