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.
Description & Operation
As altitude increases, air pressure decreases and air/fuel mixture becomes richer. High Altitude Compensation (HAC) system supplies additional air to primary low and high speed circuits on all models, and secondary high speed circuits on some models. This helps reduce emissions and improve driveability. Ignition timing is advanced for better driveability.
HAC system is designed to be functional at all altitudes. When altitude is above 3930 feet, HAC valve bellows expand and supply additional air. Components vary between the different models. See Fig 1- Fig 6 .
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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.