In a common rail system, if a nozzle valve sticks open, which device most directly limits the cylinder's fuel delivery?

• A. Rail pressure sensor
• B. Flow limiter valve
• C. Rail pressure regulator valve
• D. Unintended fuel sensor

Answer: (B)

In a common rail system, the amount of fuel a cylinder actually receives is limited not just by rail pressure or how long the injector is energized, but by a flow control device that caps how much fuel can pass to the injector. When a nozzle valve sticks open, fuel would tend to flow continuously, but the flow limiter valve acts as the final gate that restricts that flow. It sets a maximum delivery per cycle, preventing an injector fault from delivering unlimited fuel to the cylinder.

The rail pressure sensor merely monitors pressure, and the rail pressure regulator valve controls rail pressure rather than per-cycle flow to a particular injector. An unintended fuel sensor isn’t a standard component used to regulate delivery.