FAA Aviation Mechanic Powerplant (AMP)Reciprocating EnginesHard
A pilot reports that during a flight, the engine's manifold pressure gauge fluctuates erratically, especially at higher power settings. The engine operation feels rough. Which of the following is the most likely cause?
- AAn intake manifold air leak.
- BA faulty manifold pressure gauge.
- CA magneto timing issue.
- DA partially clogged fuel injector nozzle.
Show answer & explanationAnswer & explanation
Correct answer: A. An intake manifold air leak.
An intake manifold air leak allows unmetered air to enter the cylinders, leading to a lean mixture in affected cylinders. This can cause rough running due to uneven combustion and erratic manifold pressure readings as the engine struggles to maintain consistent power and airflow.
Why the other options are wrong
- B. While a faulty gauge can fluctuate, rough running points to an actual engine issue.
- C. A magneto timing issue would typically cause a more consistent power loss or roughness, or a distinct RPM drop during magneto check, rather than erratic manifold pressure fluctuations.
- D. A partially clogged fuel injector would lead to a lean condition in one cylinder, causing roughness, but manifold pressure fluctuation would be less pronounced.
Intake Manifold Air Leak
An unintended opening in the intake manifold system that allows unmetered air to enter the engine.
- Causes lean fuel/air mixture in affected cylinders.
- Leads to rough engine operation and power loss.
- Can cause fluctuating manifold pressure readings.
Memory trick: Leaky intake, lean and shaky.