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
RPBO Test Using DDDL
Test as follows:
- Install DDDL hardware.
- Start DDDL software.
- Go to “Instrumentation”, “Chart”, and select the parameter “Rail Pressure.”
- Start engine and bring to operating temperature (over 140°F/60°C).
- Turn engine OFF.
- 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.
- Monitor rail pressure trace over time.
- A normal sealed system should show the characteristics shown in the following illustration.
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- Note the time at which rail pressure reaches 280 bar.
- Note the time at which rail pressure reaches 10 bar.
- Subtract the two times from each other. Use the following worksheet.
Bleed Down Test Worksheet Time at Rail Pressure 10 bar Seconds Time at Rail Pressure 280 bar Seconds Bleed Down Time Seconds If Bleed Down Time is greater than 35 seconds, the system is OK. If Bleed Down Time is less than 35 seconds, check system for leakage -
- A system that developed a leak in the high pressure system will show the following characteristics.
- Return to symptom based diagnostic routine.
