DD 15 – Section 5.7 Rail Pressure Bleed Off

Section 5.7
Rail Pressure Bleed Off

This procedure, the Rail Pressure Bleed Off (RPBO) test will allow a technician to identify a leak in the high pressure system. A leak in one of the following locations will show a fast bleed down rate over time.‪

• High pressure pump (pumping elements)
• Fuel lines from the high pressure pump to fuel rail
• Fuel lines to each injector
• Leak at the rail pressure sensor
• Leaking pressure limiting valve
• Internal amplifier or needle leakage to the return
• Internal amplifier or needle leakage to the cylinder

Section 5.7.1
RPBO Test Using DDDL

Test as follows:‪

1. Install DDDL hardware.
2. Start DDDL software.
3. Go to “Instrumentation”, “Chart”, and select the parameter “Rail Pressure.”
4. Start engine and bring to operating temperature (over 140°F/60°C).
5. Turn engine OFF.
6. When the engine has stopped, turn ignition ON (key ON, engine OFF). Do not start.

   Note: Failure to turn the ignition back ON will cause the MCM to power down before completing the test.

7. Monitor rail pressure trace over time.
8. A normal sealed system should show the characteristics shown in the following illustration.
   
   1. Note the time at which rail pressure reaches 280 bar.
   2. Note the time at which rail pressure reaches 10 bar.
   3. Subtract the end time (10 bar) from the start time (280 bar). Use the following worksheet.

      Time noted when rail pressure reads 10 bar _______________________________‪
      Time noted when rail pressure reads 280 bar _______________________________‪
      Bleed down rate__________________________‪
      Example: ‪
      Time at 10 bar=8:19.32‪	8:19.32 – 8:18.28 = 0:01.04‪
      Time at 280 bar=8:18.28‪	One minute four seconds or 64 seconds.‪
      ‪	This engine passes a rail pressure bleed off test.‪

      Table 1. Rail Pressure Bleed Off Worksheet
9. A system that developed a leak in the high pressure system will show the following characteristics.
   
10. Return to symptom based diagnostic routine.