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 MANUALSPONTIAC1991FIREBIRD FORMULA, 5.0 F, STANDARD, M39REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETHEORY AND OPERATIONENGINE CONTROLS - THEORY & OPERATIONCOMPUTERIZED ENGINE CONTROLSOUTPUT SIGNALS
1991 Pontiac Firebird Formula, 5.0 F, Standard, M39
Output Signals
1991 Pontiac Firebird Formula, 5.0 F, Standard, M39SECTION Output Signals
NOTE:
Vehicles are equipped with different combinations of computer-controlled components. Not all components listed below are used on every vehicle. For theory and operation on each output component, refer to the system indicated after component.
- A/C Clutch - See MISCELLANEOUS CONTROLS.
- Air Injection Control Solenoid - See EMISSION SYSTEMS.
- Canister Purge Solenoid - See EMISSION SYSTEMS.
- Computer Controlled Coil Ignition (C(3)I) - See IGNITION SYSTEM.
- Cooling Fan Relay - See MISCELLANEOUS CONTROLS.
- Digital EGR Valve - See EMISSION SYSTEMS.
- Direct Ignition System (DIS) - See IGNITION SYSTEM.
- EGR Control Solenoid - See EMISSION SYSTEMS.
- ESC Timing Retard - See IGNITION SYSTEM.
- EST Timing Control - See IGNITION SYSTEM.
- Fuel Injectors - See FUEL CONTROL.
- Fuel Pump & Fuel Pump Relay - See FUEL DELIVERY.
- HEI-EST Ignition - See IGNITION SYSTEM.
- HOT Light or Coolant TEMP Light - See MISCELLANEOUS CONTROLS.
- Idle Air Control (IAC) Valve - See IDLE SPEED.
- Idle Speed Control (ISC) Motor (4.9L Cadillac) - See IDLE SPEED.
- Integrated Direct Ignition System (IDIS) - See IGNITION SYSTEM.
- Self-Diagnostics - See appropriate G - TEST W/CODES article in this section.
- Serial Data - See appropriate G - TEST W/CODES article in this section.
- "SERVICE ENGINE SOON" Light - See appropriate G - TEST W/CODES article in this section.
- Shift Light - See MISCELLANEOUS CONTROLS.
- Torque Converter Clutch - See MISCELLANEOUS CONTROLS.
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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.