Diesel injectors can suffer from the same kinds of aliments as gasoline injectors, including varnish deposits, clogging, wear and leakage.  Because diesel injectors operate at a much higher pressure than gasoline injectors, their opening pressure can drop over time.  Up to 300 psi is considered acceptable, but more than 300 psi means the injectors should be replaced or reset back to their (fully rebuilt) original operating specs.

TESTING: 1. Install a suitable pressure gauge.  2. Open the shut-off valve on the gauge a 1/4 turn.  CAUTION:  When testing nozzle opening pressure, always keep your hands (or any exposed skin) away from the nozzle.  Diesel injectors have suficient pressure to penetrate your skin!  3. Slowly depress the lever on the gauge.  Note when the needle on the gauage stops-the maximum pressure is the opening pressure.  Pressure ahould never fall below 1500 psi(10,342 kpa) on the 6.2 engines or 1700psi (11,721kpa) on the 6.5L engines.  4. As indicated above replace any injector which does not meet these pressures.

You may find that one or more injectors need nozzle tips.  Replace them with NEW BOSCH Nozzles, NOT reconditioned nozzles or knock-offs.  Both may cost less, but often do not perform.  As the spray holes wear, spray pattern and fuel atomization are affected as well.  This in turn, can have an adverse effect on fuel economy, noise and emissions.  Used nozzles tips also lose their temper from long-term exposures to operating temperatures, which means they wont hold up over the miles like a new or fully rebuilt injector.