Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSSUBARU1991LEGACY L, 4D SEDAN, AWD, STANDARDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETHEORY AND OPERATIONENGINE CONTROLS - THEORY & OPERATION
1991 Subaru Legacy L, 4D Sedan, AWD, Standard
Engine Controls - Theory & Operation
1991 Subaru Legacy L, 4D Sedan, AWD, StandardSECTION Engine Controls - Theory & Operation
- Introduction
- Air Induction System
- Computerized Engine Controls
- Engine Control Unit (Ecu)
- Input Devices (CARBURETED)
- Output Signals (CARBURETED)
- Notes
- Canister Purge Control (CPC) Solenoid Valve
- Check Engine Light
- Coasting Fuel Cut (CFC) Solenoid
- Duty Solenoid Valve (DSV)
- EGR Control Solenoid Valve
- Float Chamber Vent (FCV) Solenoid Valve
- Fuel Pump Relay
- High Altitude COMPENSATOR (HAC) Solenoid Valve - Federal
- Idle-Up Control Solenoid Valve (ICSV)
- Power Transistor
- Self-Diagnostics
- Vacuum Line Control Solenoid Valve & Vacuum/Pressure Sensor
- Input Devices (Fuel Injection)
- Notes
- A/C Switch
- Airflow Meter (Except JUSTY)
- Air Temperature Sensor (JUSTY)
- Atmospheric Pressure Sensor
- Cam Angle Sensor (Legacy)
- Coolant Temperature Sensor
- Crank Angle Sensor (Legacy)
- Crank Angle & TDC (Cylinder Id) Sensor Assembly (Exc. Legacy)
- Detonation (Knock) Sensor
- Idle Switch
- Inhibitor Switch (A/T)
- Neutral & Park Switches
- Oxygen (O2) Sensor
- Pressure Switch (Turbo)
- Throttle Sensor (Except JUSTY)
- Throttle Switch (JUSTY)
- Vehicle Speed Sensor
- Output Signals (Fuel Injection)
- Notes
- Auxiliary Air Valve
- By-Pass Air Control Valve
- Canister Purge Control (CPC) Solenoid
- Check Engine Light
- Detonation (Knock) Sensor
- EGR Control Solenoid Valve
- Fast Idle Control Device (FICD) Solenoid Valve
- Fuel Injector Resistor Pack
- Fuel Injector(S) (Fuel Control - TBI Or PFI)
- Fuel Pump Relay (Fuel Delivery - Fuel Injection)
- Power Transistor (Ignition System)
- Self-Diagnostics (Self-Diagnostics)
- Fuel System (CARBURETED)
- Fuel System (Fuel Injection)
- Ignition System
- Emission Systems
- Self-Diagnostics
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.