Jeep Cherokee 1988 User Manual

2.5L CEC SYSTEM
1988 Jeep Cherokee
1988 Computerized Engine Controls
JEEP 4-CYLINDER 2.5L TBI COMPUTERIZED EMISSION CONTROL
Cherokee, Comanche
DESCRIPTION
The computerized engine control system, used on 2.5L models
with throttle body fuel injection, is built around an electronic
control unit (ECU). The ECU is a microprocessor-based computer.
The major function of the system is to reduce emissions. It
accomplishes this through a series of 13 sensors or switches that
constantly monitor several engine conditions. See Fig. 16.
Fig. 1: Vacuum Diagram for Jeep 2.5L CEC System
The computer processes input information from the sensors to
get an accurate picture of engine operation. It then provides output
control signals to regulate air/fuel ratio, ignition, idle speed and

Jeep Cherokee 1988 Specifications

General

Brand	Jeep
Model	Cherokee 1988
Category	Automobile
Language	English

Summary

DESCRIPTION

OPERATION

ELECTRONIC CONTROL UNIT (ECU)

Explains the function and location of the ECU.

SENSORS & SWITCHES

Details the various sensors and switches used in the system.

Exhaust Gas Oxygen (EGO) Sensor

Describes the EGO sensor's function and operation.

Manifold Air/Fuel Temperature (MAT) Sensor

Explains the MAT sensor's role in engine control.

Coolant Temperature Sensor (CTS)

Details the CTS function in monitoring engine temperature.

Manifold Absolute Pressure (MAP) Sensor

Describes the MAP sensor's function and location.

Knock Sensor

Explains the knock sensor's role in preventing detonation.

Speed Sensor

Describes the speed sensor's function in calculating engine speed.

Battery Voltage

Explains how battery voltage is monitored by the ECU.

Starter Motor Relay

Describes the starter motor relay input to the ECU.

Wide Open Throttle (WOT) Switch

Details the WOT switch's function and ECU response.

Closed Throttle (Idle) Switch

Explains the closed throttle switch's role in idle speed control.

Transmission Gear Position Indicator

Describes the gear position indicator input to the ECU.

Power Steering Pressure Switch

Explains the power steering switch function.

A/C Switch

Describes the A/C switch input to the ECU.

FUEL CONTROL

EMISSION CONTROL

IDLE SPEED ACTUATOR (ISA)

IGNITION ADVANCE CONTROL

ECU-CONTROLLED RELAYS

Load Swap Relay

Describes the load swap relay's function.

Fuel Pump Control Relay

Explains the fuel pump relay operation.

A/C Clutch Relay

Describes the A/C clutch relay.

UP-SHIFT INDICATOR LAMP

MODES OF OPERATION

IGNITION SWITCH "ON" MODE

Describes system behavior with ignition on.

ENGINE START-UP MODE

Explains ECU actions during engine start-up.

ENGINE WARM-UP MODE

Details ECU control during engine warm-up.

CRUISE MODE

Describes ECU functions during cruising.

DECELERATION MODE

Explains ECU actions during deceleration.

WIDE OPEN THROTTLE MODE

Describes ECU control during WOT.

IGNITION SWITCH "OFF" MODE

Explains system behavior when ignition is off.

COMPONENT TESTING

COOLANT TEMPERATURE SENSOR

Testing procedures for the CTS.

WIDE OPEN THROTTLE (WOT) SWITCH

Testing procedures for the WOT switch.

CLOSED THROTTLE SWITCH

Testing procedures for the closed throttle switch.

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR

Testing procedures for the MAP sensor.

THROTTLE POSITION SENSOR TEST

Testing procedures for the Throttle Position Sensor.

BASIC ENGINE TEST

Procedures for basic engine diagnostics.

MAN. TRANS. UP-SHIFT TEST

Testing the manual transmission up-shift indicator.

ELECTRONIC CONTROL UNIT

SYSTEM DIAGNOSIS

PRELIMINARY CHECKS

Initial checks before detailed diagnosis.

DIAGNOSTIC TEST CHARTS

Lists various diagnostic test flows.

ECU Connector Terminal Identification

Identifies ECU connector pin assignments.

REMOVAL & INSTALLATION

THROTTLE BODY ASSEMBLY

Removal and installation of the throttle body.

FUEL INJECTOR

Removal and installation of the fuel injector.

FUEL PRESSURE REGULATOR

Removal and installation of the fuel pressure regulator.

IDLE SPEED ACTUATOR, MOTOR & WIDE OPEN THROTTLE SWITCH

Removal and installation of ISA and WOT switch.

ELECTRONIC CONTROL UNIT

Removal and installation of the ECU.

OXYGEN SENSOR

Removal and installation of the oxygen sensor.

MANIFOLD AIR TEMPERATURE & MANIFOLD ABSOLUTE PRESSURE SENSORS

Removal and installation of MAT and MAP sensors.

COOLANT TEMPERATURE SENSOR (CTS)

Removal and installation of the CTS.

EGR VALVE & CANISTER PURGE SOLENOID

Removal and installation of EGR/purge solenoid.

ADJUSTMENTS

IDLE SPEED ACTUATOR (ISA) MOTOR

Adjustment procedures for the ISA motor.

WIDE OPEN THROTTLE SWITCH

Adjustment procedures for the WOT switch.

FUEL PRESSURE REGULATOR