FAA Powerplant Written Practice Test

What does a manifold pressure gauge indicate?

1. Atmospheric pressure outside the engine

2. Absolute pressure in the intake manifold

3. Pressure fluctuations in the fuel system

4. Dynamic pressure in the exhaust system

The correct answer is: Absolute pressure in the intake manifold

A manifold pressure gauge indicates the absolute pressure in the intake manifold of a reciprocating engine. This measurement is crucial for understanding the engine's performance as it directly reflects the air-fuel mixture available for combustion. The gauge reads pressure in inches of mercury (inHg) or kilopascals (kPa), which helps pilots and technicians assess engine condition and efficiency. When an engine is operating normally, the manifold pressure will vary according to throttle position, altitude, and engine load, making it an essential tool for monitoring engine performance. Understanding the manifold pressure is vital for managing engine operations, as it can influence fuel flow and engine power output. Properly reading and interpreting this gauge allows for adjustments that ensure optimal performance and efficiency. While atmospheric pressure outside the engine, fuel system fluctuations, and exhaust system dynamics may affect engine performance, they are not directly indicated by the manifold pressure gauge. The gauge specifically conveys information about the pressure within the intake manifold, making it a key instrument for engine analysis and performance adjustment.