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Fuel pressure limits with fuel injection

Aviation Mechanic Powerplant (AMP) practice question 6 of 12 on Engine Instrument Systems. ACS element AM.III.D.K4 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONAn engine using a fuel injection system indicates 8 psi on its fuel pressure gauge. Compared with the pressures the handbook gives for fuel injection systems, what does this reading show?

  1. APressure is below the minimum
  2. BPressure is in the normal range
  3. CPressure has exceeded the maximum
Show the answer and explanation

Correct answer: A. Pressure is below the minimum

  • A — correct For fuel injection systems the minimum allowable pressure is approximately 10 psi, so an indication of 8 psi falls short of it.
  • B — incorrect The normal band for fuel injection runs from roughly 10 psi to about 25 psi, and 8 psi lies under that band.
  • C — incorrect The maximum for a fuel injection system is generally 25 psi, far above the indicated value.

BACKGROUND

The fuel pressure gauge is calibrated in pounds per square inch (psi) and shows engine fuel pressure at points such as the carburetor inlet or the main fuel supply line. Fuel pressures vary with the type of fuel system and the size of the engine, so the markings differ between installations. On the carburetor-equipped example described in the powerplant handbook, a red line at 2 psi is the minimum permitted in flight, a green arc covers 2 to 9 psi, and a red line at 9 psi is the maximum allowable. When a fuel injection system is used, the pressure range is much higher: the minimum allowable pressure is approximately 10 psi and the maximum is generally 25 psi. Comparing an indication against the correct set of limits for the installation is what makes the reading meaningful.

STUDY TIP

Keep the two sets of numbers separate: about 2 to 9 psi for the carburetor example and about 10 to 25 psi for fuel injection.

KEY POINTS

  • Fuel injection minimum is approximately 10 psi; maximum is generally 25 psi.
  • The carburetor example is marked 2 psi minimum, 2 to 9 psi green, 9 psi maximum.
  • Fuel pressure limits depend on the system type and engine size.

SOURCES

  • FAA-H-8083-32B ch10 "Fuel Pressure Indicator"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-32B Aviation Maintenance Technician Handbook – Powerplant, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.