Which test method is used to detect leaking injectors by monitoring rail pressure while isolating the injector?

• A. Listening with a stethoscope.
• B. Visual inspection of injector wiring.
• C. Pressure hold test by isolating the injector and monitoring rail pressure.
• D. Disconnecting the battery while the engine is running.

Answer: (C)

Focusing on how an injector behaves when it’s shut off is the key. In a high-pressure rail system, a leaking injector will allow fuel to escape past its seat even when it’s not commanded to spray. The pressure hold test does exactly that: you bring the rail up to spec, then isolate a single injector and watch the rail pressure. If the injector is sealing properly, the rail pressure should stay steady. If there’s a leak through that injector, the pressure will fall as fuel leaks past the injector into the cylinder or back toward the rail, revealing the faulty unit.

This method directly tests the injector’s sealing integrity under closed conditions, which is why it’s the best fit for detecting leaking injectors. Other options aren’t as effective: listening with a stethoscope can miss leaks and only confirms audible noise, visual wiring checks don’t address fuel leakage, and disconnecting the battery while the engine runs doesn’t test injector sealing and is unsafe.