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Fuel introduction point on a fuel-injected engine

Aviation Mechanic Powerplant (AMP) practice question 4 of 13 on Reciprocating Engine Induction and Cooling Systems. ACS element AM.III.J.K1 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONOn a fuel-injected reciprocating engine, at what point is fuel introduced into the induction air?

  1. AAt the intake port just before the intake valve
  2. BAt the air scoop just ahead of the induction filter
  3. CIn the throttle body at the induction manifold inlet
Show the answer and explanation

Correct answer: A. At the intake port just before the intake valve

  • A — correct On fuel-injected engines the fuel is injected at the intake port just before the intake valve, so it is important to keep the pressure consistent at each intake port.
  • B — incorrect The air scoop only collects inlet air and the filter removes dirt; no fuel is added at that point.
  • C — incorrect That describes a carbureted arrangement, where the fuel metering device adds fuel upstream of the manifold; an injected engine adds fuel much farther downstream.

BACKGROUND

The basic induction system of an aircraft reciprocating engine consists of an air scoop that collects inlet air and ducting that carries the air to the inlet filter. The filtered air then passes through a fuel metering device, which on light aircraft is either a carburetor or a fuel-injection system. With a carburetor, fuel is added at the metering device and the air-fuel mixture travels through the intake manifold to the cylinders. With fuel injection, only air travels through the manifold and the fuel is injected at each intake port just before the intake valve. Because of this, even port pressure is critical on an injected engine, while even induction pressure is critical on a carbureted one.

STUDY TIP

Fix the order of components in your head: scoop, duct, filter, metering device, manifold, intake port. Then ask where the fuel joins the air for the system in question.

KEY POINTS

  • Fuel-injected engines inject fuel at the intake port just before the intake valve.
  • Carbureted engines mix fuel and air at the fuel metering device, upstream of the manifold.
  • Consistent pressure at each intake port matters most on an injected engine.

SOURCES

  • amp-powerplant/ch03.txt "Reciprocating Engine Induction Systems"
Practice the Aviation Mechanic Powerplant (AMP) test →Timed 100-question exam, by ACS area, or review your misses. Free.
MORE ON RECIPROCATING ENGINE INDUCTION AND COOLING SYSTEMS

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.