1968 Shelby GT500

No Codes?

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The famous

•Check Battery voltage, must be above 10.5 volts.
     •Replace battery if not.
•Check battery connections, corrosion, ground faults, and wiring.
    • Fix all wiring.
•Check alternator output, must be between 13.5 and 14.5 volts.
    •Replace Alternator if not.
    •Any recent voltage irregularities from electrical charging system can cause failures.
     •Replace alternator and any damaged circuits, wiring, and components.
•Check fusible links on Starter Solenoid if equipped.
•Check fuses and surge protection diode in under hood Power Distribution Box.
     •Replace any fuses, diodes, and links if needed.
•Check EEC relay, must show battery voltage when engaged.
     •Replace relay and damaged wiring if not.
•Make sure pin 30 on the computer is hooked up correctly.
      •Manual transmission computers need to sense SIG-RTN on pin 30 when in neutral.
     •Automatic transmission computers need to sense Ground on pin 30 when in neutral.
      •Electronicly controled automatic computers need an operational Manual Lever Position Sensor (MLPS)
•Check aftermarket devices like alarm system connected to engine or computer components.
     •Restore engine and computer system to original configuration.
•Check aftermarket computer chips and other plug in controls.
     •Any chips or controls that impede basic engine and computer function need to be removed.
     •Restore computer and harness to original configuration.
•Disconnect computer and inspect for damaged or pushed out pins, corrosion, loose wires.
     •Replace computer if visually damaged, repair any damaged pins in harness.
•Visually inspect the ENTIRE engine and computer wiring harness and connections for corrosion, ground faults, shorts, physical damage, and general condition.
     •FIX ANY & ALL PROBLEMS!
•Check Self-Test Input circuit on Pin 48 at computer harness for shorts to ground.
     •Replace faulty wiring.
•Remove check engine light bulb and check Self-Test Output circuit for shorts to ground.
      •Replace faulty wiring.
     •Check Engine Light for damage.
     •Replace faulty light bulb.
•Measure resistance between battery negative post and pins 20, 40, and 60 at the computer harness.
     •Resistance must be less than 5.0 ohms.
     •Replace faulty wiring between computer and battery if not.
•Turn key to ON with engine OFF and computer removed. Measure voltage on pins 1, 37, and 57. Must be above 10.5 volts and within 1.0 volt of each other.
     •Replace faulty wiring between computer and battery if not.
•Turn key ON with engine OFF and computer reinstalled. Measure voltage between Pin 26 and 46 (voltage reference and signal return) must be between 4.0-6.0 volts.
      •Replace faulty wiring and sensors.
•Measure resistance between Pin 46 and Pins 40 and 60 at the computer harness, must be less than 5.0 ohms.
     •If all the wiring and sensors check out, Replace the computer.

Complete list of 2-Digit Self-Test Codes and their definitions.
Complete list of 3-Digit Self-Test Codes and their definitions.

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