Reciprocation Engine Induction And Cooling Systems Oral Practice Test

In higher altitude driving, what must happen in the ECU to maintain proper air-fuel mixtures?

It ignores altitude changes. It compensates for air density changes due to altitude. It disables fueling adjustments at high altitude. It increases injector size automatically.

Correct Answer:

It compensates for air density changes due to altitude.

Explanation:

When you climb to higher altitude, the air is thinner, so there are fewer oxygen molecules in each intake. To keep the air-fuel mixture near the target ratio (about 14.7:1 for gasoline), the ECU adjusts fuel delivery based on sensors that estimate how much air is entering the engine and how the engine is running. It uses measurements from the air intake (MAP or MAF), RPM, throttle position, and temperature, and it relies on the oxygen sensor in the exhaust to fine-tune fueling. Through short-term and long-term fuel trims, the ECU maintains a proper mixture as altitude changes. It doesn’t ignore altitude, disable fueling, or automatically increase injector size; it modulates the injector pulse width to keep the mixture correct.

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