What could cause a fuel pressure gauge to fluctuate?

• A. Electrical interference
• B. The loss of the light oil in the line between the gauge and the engine
• C. The temperature change in cockpit
• D. Altitude change

Answer: (B)

Fuel pressure readings tend to pulse because the engine fuel pump delivers fuel in cycles. To keep the gauge reading steady, the line from the engine to the gauge includes a dampening section filled with light oil that smooths those pulses. If that dampening oil leaks away, the line loses its ability to dampen the pulses, so the pulsations are transmitted directly to the gauge and you see fluctuations. Temperature changes in the cockpit or altitude shifts don’t directly cause this kind of damping failure, and electrical interference would typically produce different kinds of gauge behavior. So the loss of the light oil in the line between the gauge and the engine is the best explanation for fluctuating readings.