FAA Powerplant Written Practice Test

What does a manifold pressure gauge indicate?

1. Relative pressure in the crankcase

2. Absolute pressure in the intake manifold

3. Vacuum pressure in the fuel system

4. Pressure in the exhaust manifold

The correct answer is: Absolute pressure in the intake manifold

The manifold pressure gauge is specifically designed to measure the absolute pressure within the intake manifold of an engine. This measurement is crucial because it helps determine the engine’s performance based on how much air is being drawn into the cylinders for combustion. Understanding manifold pressure is important for managing engine efficiency, as it directly relates to the air-fuel mixture and the engine’s ability to produce power. It aids pilots and mechanics in assessing the engine's operation under various conditions, including different altitudes and power settings. The other options refer to measurements that do not pertain to the primary function of the manifold pressure gauge. For instance, the crankcase pressure is not measured by this gauge, and vacuum pressure in the fuel system relates to fuel delivery rather than intake air. Additionally, pressure in the exhaust manifold does not involve the intake system that the manifold pressure gauge monitors.