Massey Ferguson 520319.31 – Engine ECU: Rail Pressure control: Pressure out of range in limp home mode

The engine's common rail fuel system is failing to maintain the requested fuel pressure while the tractor is operating in a restricted power state (limp mode/active derate).

• 4710
• 7724S
• 5712SL
• 7722S
• 7722
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 4708
• 7726S
• 4707
• 4709
• 5711SL
• 7718S
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 7720
• Tier 4 (2015-2021)
• 7715S
• 7724
• 4600 Series
• 4700 Series
• 4608
• 4609
• 4610
• 5400 Series
• 5600 Series
• 5700 Series
• 5465
• 5475
• 5611
• 5612
• 5710
• 5711
• 6400 Series
• 6600 Series
• 6700 Series
• 6465
• 6480
• 6497
• 6614
• 6713
• 7400 Series
• 7600 Series
• 7700 Series
• 7465
• 7490
• 7620
• 8400 Series
• 8600 Series
• 8700 Series
• 8450
• 8480
• 8650
• 8730
• 8740

1. 1

   Check for plugged fuel filters, which are a primary cause of low fuel pressure.

2. 2

   Check for air intrusion in the fuel lines or a leak on the inlet side of the fuel pump.

3. 3

   Inspect the fuel tank, fuel lines, and check valves for debris or restrictions.

4. 4

   Inspect the wiring harness and connector to the fuel rail pressure sensor for shorts to ground, shorts to battery voltage, or open circuits.

5. 5

   Use a diagnostic tool to monitor the actual fuel rail pressure versus the requested fuel rail pressure to see if the pressure is dropping under load or spiking erratically.

6. 6

   Determine if the mechanical fuel pressure relief valve (pressure limit valve) on the rail is stuck open or leaking fuel back to the return line prematurely.

1. 1

   Filter Maintenance

   Replace the primary and secondary fuel filters and bleed the fuel system to ensure no air is trapped. Clear the code and test the tractor.

2. 2

   Cleanliness Prep

   If opening the high-pressure fuel system, thoroughly clean the area around the fuel rail. Extreme cleanliness is required, as microscopic contamination can destroy common rail components.

3. 3

   Relief Valve Replacement

   If diagnostics point to a failure to hold pressure, replace the Rail Pressure Relief Valve. Relieve system pressure, unthread the old valve from the fuel rail, install the new valve, and torque to OEM specifications.

4. 4

   Sensor Replacement

   If the sensor is reading out of range or has an internal electrical fault, replace the Fuel Rail Pressure Sensor.

5. 5

   System Prime

   Prime the fuel system with fresh, filtered fuel before cranking the engine.

6. 6

   Clear Codes

   Use a diagnostic tool to clear the 520319.31 fault code and run the tractor under load to verify the repair.