Reciprocation Engine Induction And Cooling Systems Oral Practice Test

What does a correctly functioning MAP sensor indicate during idle, part-throttle, and full-throttle?

MAP reads ambient pressure at idle. MAP reads vacuum at idle and stays there. MAP reads near vacuum at idle, then increases with load, and at full-throttle approaches ambient pressure plus boost. MAP reads only atmospheric pressure and is not influenced by boost.

Correct Answer:

MAP reads near vacuum at idle, then increases with load, and at full-throttle approaches ambient pressure plus boost.

Explanation:

The MAP sensor measures the pressure inside the intake manifold, which changes as engine load changes. At idle, the throttle is mostly closed, creating a strong vacuum in the manifold, so the sensor reads a low absolute pressure. As you move to part-throttle, the throttle opens more, vacuum drops, and manifold pressure climbs toward ambient. At full-throttle on a boosted engine, the turbo or supercharger pushes air into the manifold, pushing the pressure above ambient—so the MAP approaches ambient pressure plus the boost. This sequence—near vacuum at idle, increasing with load, and approaching ambient plus boost at full throttle—best describes a correctly functioning MAP sensor. The other descriptions ignore how manifold pressure actually varies with load and boost.

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