Wear is inevitable over hundreds of thousands of cycles. Symptoms of a worn barrel and plunger are often related to a loss of ability to generate and hold peak injection pressure:

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  Hard Starting, Especially When Hot: This is a classic sign. As the metal expands with heat, the clearances in a worn set increase, allowing fuel to leak past the plunger more easily, reducing pressure needed to start.

  
  


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  Loss of Power Under Load: The engine may idle fine but struggle to produce full power because it cannot deliver a full, high-pressure shot of fuel when demanded.

  
  


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  Poor Fuel Economy: Inaccurate metering and pressure loss mean the engine isn't burning fuel efficiently.

  
  


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  Excessive Black Smoke: Incomplete combustion due to poorly atomized fuel (from low injection pressure) results in unburnt fuel exiting as black smoke.

  
  


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  Rough Idle or Misfiring: Inconsistent pressure between cylinders can cause a rough run pattern.

  
  

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