1987-1990 Renix System Manual

The Renix fuel injection system was used in Jeep vehicles from 1987-1990, featuring an integrated engine management system with electronic fuel injection, ignition control, and various sensors. This system includes the Renix ECU, throttle body injection, MAP sensor, coolant temperature sensor, crankshaft position sensor, and oxygen sensor. Below are key sections for system overview, components, installation, troubleshooting, specifications, and maintenance procedures.

1. System Overview 2. Component Identification 3. Installation Procedures 4. Technical Specifications 5. Sensor Locations 6. Wiring Diagrams 7. Diagnostic Procedures 8. Maintenance Schedule 9. Calibration Settings 10. Troubleshooting Guide

System Overview

The Renix system is a multi-point fuel injection system designed for 4.0L and 2.5L engines, providing precise fuel metering and ignition timing control through electronic sensors and actuators.

Component	Function
Renix ECU	Main control unit for fuel and ignition timing
MAP Sensor	Measures manifold absolute pressure
Throttle Position Sensor	Monitors throttle plate position
Coolant Temp Sensor	Provides engine temperature data
Crankshaft Position Sensor	Detects engine RPM and position
Oxygen Sensor	Monitors exhaust oxygen content
Idle Air Controller	Regulates idle speed
Fuel Injectors	Delivers precise fuel amounts
Ignition Control Module	Controls spark timing
System Relay	Powers ECU and fuel pump

Component Identification

Locate and identify all Renix system components for proper maintenance and troubleshooting.

ECU Location: Under dashboard, passenger side
MAP Sensor: Mounted on firewall or intake manifold
TPS: Attached to throttle body shaft
CPS: Mounted on bellhousing near flywheel
O2 Sensor: In exhaust manifold or downpipe
Coolant Sensor: In thermostat housing or cylinder head

WARNING! Disconnect battery before servicing electrical components to prevent short circuits.

Installation Procedures

Proper installation ensures optimal Renix system performance and reliability.

ECU Installation: Secure in mounting bracket, connect 60-pin connector
Sensor Installation: Apply anti-seize to threads, torque to specifications
Wiring Harness: Route away from heat sources and moving components
Ground Connections: Clean contact surfaces for proper electrical grounding
Final Check: Verify all connections before battery reconnection

CAUTION! Use proper torque values to avoid sensor damage.

Technical Specifications

System Type: Multi-point fuel injection
Fuel Pressure: 31 psi (idle), 39 psi (with vacuum disconnected)
Injector Flow Rate: 19 lbs/hr at 39 psi
Ignition Timing: 12° BTDC (set with connector disconnected)
Idle Speed: 750 RPM (in drive for automatics)
TPS Voltage: 0.8V at closed throttle, 4.5V at WOT
MAP Sensor: 1.0-1.5V at idle, 4.5V at WOT
Operating Voltage: 12V DC system
Temperature Range: -40°F to 250°F operating

Sensor Locations

Proper sensor location is critical for accurate system operation and diagnostics.

Primary Sensors: MAP sensor (firewall), TPS (throttle body), CPS (bellhousing), CTS (thermostat housing), O2 sensor (exhaust manifold).

Secondary Sensors: Vehicle speed sensor (transfer case), knock sensor (block), barometric pressure sensor (integrated in MAP). Grounds: Engine block, firewall, cylinder head. Connectors: Weather-pack style, color-coded for identification.

Wiring Diagrams

Reference wiring diagrams for proper circuit identification and troubleshooting.

ECU Connector: 60-pin configuration with pinout identification
Sensor Circuits: 5V reference, signal return, sensor ground
Power Distribution: Battery, ignition switch, system relay
Ground Circuits: Engine, chassis, sensor grounds

Tip: Use DVOM for voltage and resistance measurements during diagnostics.

Diagnostic Procedures

Systematic approach to Renix system diagnostics and repair.

Visual Inspection: Check connectors, wiring, vacuum lines
Code Retrieval: Ground diagnostic connector to flash codes
Sensor Testing: Measure resistance and voltage outputs
Fuel System: Check pressure and injector pulse
Ignition System: Verify spark output and timing
Data Monitoring: Use scan tool for live data (if available)
Component Replacement: Test new components before installation
System Verification: Road test for performance confirmation

WARNING! Always disconnect battery before electrical testing to prevent ECU damage.

Maintenance Schedule

Regular maintenance ensures long-term Renix system reliability and performance.

Calibration Settings

Proper calibration is essential for optimal engine performance and emissions compliance.

CAUTION! Use factory specifications for all adjustments.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
No start condition	CPS failure, fuel pump, ignition	Test CPS signal, check fuel pressure, verify spark
Poor idle quality	Vacuum leaks, IAC, TPS	Smoke test for leaks, test IAC operation, calibrate TPS
Hesitation/stumbling	MAP sensor, fuel pressure	Test MAP output, verify fuel pressure under load
High fuel consumption	O2 sensor, coolant sensor	Test O2 sensor switching, verify CTS resistance
Rough running	Ignition components, injectors	Check plugs/wires, test injector balance

Reset: Disconnect battery for 30 minutes to clear adaptive memory.

Technical Support: Refer to factory service bulletins for updates