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.
High Altitude Compensation System: Description
The high altitude compensating system consists of the Electronic Control Module (ECM), an altitude switch, and a solenoid valve. The altitude switch senses altitude from atmospheric pressure and activates solenoid valve and ECM at high altitude.
The solenoid valve opens an leans air/fuel mixture by introducing air into the carburetor through the altitude compensating ports. The ECM changes the open duty cycle and also leans the air/fuel ratio. The lean mixture reduces HC and CO emissions at high altitudes. At low altitude the altitude compensating system does not operate.
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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.