You do not need to immediately pull the injector to suspect barrel and plunger wear. There are three classic symptoms that point directly to this specific failure mode:

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  Symptom 1: Erratic Idle with Black Smoke. If the plunger is worn, it cannot seal consistently at low speeds. Fuel dribbles past the plunger at the wrong time, causing a "lumpy" idle and a haze of black smoke that does not clear up with tuning.

  
  


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  Symptom 2: Low Power with "Clean" Exhaust. A worn set cannot generate high injection pressure. The fuel leaves the tip as large droplets rather than a fine mist. This results in incomplete combustion, but surprisingly, the smoke may look white or gray rather than black. The engine feels flat.

  
  


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  Symptom 3: Fuel Dilution of Engine Oil. This is the definitive indicator. If the plunger is severely worn, high-pressure fuel blows past the plunger, down the injector body, and into the valve cover area. It then drains into the oil pan. If your oil level is rising and it smells like diesel, your barrel and plunger are failing.