FAA Aviation Mechanic Powerplant (AMP)Fuel, Induction and LubricationMedium
A mechanic is troubleshooting a continuous-flow fuel injection system on a reciprocating engine. The pilot reports that the engine runs rough at idle and stalls frequently. After checking fuel pressure and flow, the mechanic suspects an issue with the fuel manifold valve (flow divider). What is the most likely symptom of a malfunctioning fuel manifold valve related to this complaint?
- AContinuous fuel spray from the nozzles after engine shutdown.
- BUneven fuel distribution to the individual cylinders.
- CExcessively high fuel pressure at all engine speeds.
- DComplete loss of fuel flow to all cylinders.
Show answer & explanationAnswer & explanation
Correct answer: B. Uneven fuel distribution to the individual cylinders.
The fuel manifold valve (flow divider) is responsible for distributing fuel evenly to each cylinder's nozzle. If it malfunctions, it can cause uneven fuel flow, leading to a rough idle and frequent stalling as some cylinders run too rich or too lean.
Why the other options are wrong
- A. Continuous fuel spray after shutdown is typically caused by a leaking fuel nozzle or a problem with the fuel shutoff valve, not the manifold valve's ability to divide flow during operation.
- C. Excessively high fuel pressure at all engine speeds would typically be caused by a problem with the relief valve or a restriction upstream of the manifold valve, not the manifold valve itself causing rough idle.
- D. A complete loss of fuel flow to all cylinders would typically be a more severe issue like a pump failure or a main fuel line blockage, not usually a manifold valve malfunction causing only rough idle.
Fuel Manifold Valve Function
The fuel manifold valve (flow divider) in a continuous-flow fuel injection system evenly distributes metered fuel to each engine cylinder's fuel nozzle.
- Ensures equal fuel delivery to all cylinders for smooth operation.
- Contains a diaphragm and spring to open at a specific pressure.
- If faulty, can cause rough running, especially at idle, due to uneven distribution.
Memory trick: Manifold's Mission: Make Mixture Match