Definition
The fuel pressure measured in a fuel injection system at the point after the engine-driven fuel pump but before the fuel metering unit (the device that controls how much fuel is delivered to the engine). It represents the supply pressure available to the metering system and is one of the values used to verify correct fuel system operation during ground checks and troubleshooting.
Plain English
The fuel pressure on the pump side of the system, measured before the fuel has been adjusted into the precise amount the engine needs. It tells a technician whether the pump is delivering fuel to the metering unit at the correct pressure.
Context Anchor
Seen during engine fuel-system troubleshooting, fuel pressure checks, and maintenance run-ups.
Derivation
Unmetered means 'not yet measured out.' A meter is a device that measures or controls a flow. So unmetered fuel is fuel that has not yet passed through the metering unit, where its quantity is controlled before reaching the engine.
Why Pilots Care
Low unmetered fuel pressure reduces fuel delivery to the engine and can cause power loss, rough running, or complete engine stoppage.
Analogy
It is like low water pressure before a spray nozzle. The nozzle can only control the spray properly if enough water reaches it first.
Intuition Check
“Unmetered” does not mean bad or wasted fuel. It means fuel before the system has measured and controlled the amount going to the engine. “Low” means below the required system value, not just a small-looking number.
Example Sentence 1
During the engine ground run, the technician checked low unmetered fuel pressure to confirm the engine-driven pump was delivering the correct supply pressure to the fuel control.
Example Sentence 2
After replacing the electric boost pump, the low unmetered fuel pressure reading returned to the normal range specified in the maintenance manual.