Massey Ferguson 520229.31 – Engine ECU: Fuel Rail Pressure Not Dropping As Expected

The engine's control system has commanded a decrease in the high-pressure fuel rail pressure, but the actual pressure measured by the rail pressure sensor is remaining too high. This indicates a mechanical or hydraulic inability to bleed off or regulate the fuel pressure down to the target level.

• 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
• MF 5400
• MF 6400
• MF 7400
• MF 8400
• MF 8600
• MF 8700

1. 1

   Connect a diagnostic tool and monitor 'Commanded Fuel Rail Pressure' versus 'Actual Fuel Rail Pressure'. Verify that the actual pressure is hanging high when the commanded pressure drops (e.g., when returning to idle).

2. 2

   Check the fuel return lines running from the fuel rail and the high-pressure pump back to the fuel tank. A kinked, crushed, or blocked return line will prevent pressure from bleeding off.

3. 3

   Check the fuel rail pressure sensor wiring harness for shorts or high resistance that could cause a skewed (falsely high) voltage reading.

4. 4

   Test the Suction Control Valve (SCV / MPROP) on the high-pressure pump and the Fuel Rail Pressure Relief Valve (PRV) for sticking or malfunctioning.

1. 1

   Clear Return Lines

   If any kinks or blockages were found in the fuel return lines during diagnosis, clear or replace the lines.

2. 2

   Replace the Suction Control Valve (SCV)

   If the return lines are clear, the primary culprit for over-pressurization is a sticking SCV (MPROP valve). Thoroughly clean the area around the high-pressure pump, remove the SCV mounting bolts, and install a new SCV with new O-rings.

3. 3

   Replace the Pressure Relief Valve (PRV)

   If replacing the SCV does not resolve the issue, the PRV on the fuel rail may be mechanically seized closed. Remove the old PRV from the fuel rail and torque the new valve to OEM specifications.

4. 4

   Maintain Cleanliness

   Extreme cleanliness is required when working on the common rail system. Even microscopic contamination can destroy components. Always use fresh, filtered fuel when priming the system.

5. 5

   Clear Codes and Test

   Use a diagnostic tool to clear the 520229.31 DTC. Run the engine and monitor the live fuel rail pressure data to ensure it now accurately tracks the commanded pressure.