Because the PT injector is a mechanically driven, precision component operating under extreme heat and pressure, it is subject to specific wear patterns and failure modes. Diagnosing these correctly is key to keeping an old Cummins (like an NH, NT, or N14) running strong.
Here are the three most common issues:
Plunger and Barrel Wear (The "Stiction" Problem): The injector plunger fits inside the barrel with a clearance measured in millionths of an inch. Over hundreds of thousands of miles, contaminants in the fuel or simple wear can increase this clearance. This allows fuel to leak past the plunger during the injection event.
Symptoms: Hard starting, low power, misfiring at idle, and "white smoke" from unburned fuel. In severe cases, the plunger can scuff or seize in the barrel.