Case IH 3921 – EDC (Electronic Diesel Control): Fuel pressure (Rail) control: Leakage in high pressure system with empty tank.

This code indicates that the engine control system has detected a significant drop in fuel rail pressure, interpreted as a high-pressure fuel leak, specifically occurring when the fuel tank is empty or drawing air. The system's Metering Unit (MeUn) is unable to maintain the commanded fuel rail pressure because the high-pressure pump is being starved of fuel or there is an actual physical leak in the high-pressure circuit (injectors, rail, or pump).

• Maxxum 110
• Maxxum 120
• Maxxum 130 Multicontroller
• Puma 205
• Puma 225
• Steiger 380
• Steiger 385
• Steiger 430
• Steiger 435
• Steiger 485
• STX380
• STX430
• STX450
• STX500
• Farmall 115U

1. 1

   Verify fuel level to ensure the fuel tank is not empty, as the code specifically triggers under empty tank or air-draw conditions.

2. 2

   Check for air ingress by installing a clear test line between the fuel filter and the high-pressure pump inlet. Run the engine and observe for a steady stream of air bubbles.

3. 3

   Test low-pressure fuel supply between the filter and the high-pressure pump (should be a minimum of 5 bar/72 psi, or 0.276-0.414 bar/4-6 psi depending on lift pump setup).

4. 4

   Inspect the fuel pre-filter, main fuel filters, and all Voss O-ring fittings for restrictions or air leaks.

5. 5

   Perform a fuel leakage rate test on the electronically controlled injectors to check for excessive return fuel (injector leak-off).

6. 6

   Test the Metering Unit (MeUn) pressure control on the high-pressure pump inlet regulator to ensure it is commanding fuel properly.

1. 1

   Refuel and Prime

   If the tank was run empty, fill the fuel tank and thoroughly bleed the low-pressure and high-pressure fuel systems to remove all air. Clear the fault code and test run the machine.

2. 2

   Resolve Low-Pressure Issues

   If air ingress or low pressure was found during diagnostics, replace the primary and secondary fuel filters. Inspect the fuel lines from the tank to the lift pump. Replace any degraded Voss O-ring fittings that may be sucking air.

3. 3

   Clean the Tank

   If the lift pump screen is clogged, drain and clean the fuel tank to remove debris from the bottom/sidewalls.

4. 4

   Replace Leaking High-Pressure Components

   If the low-pressure side is perfect and the code persists (indicating a true high-pressure leak): If the injector leak-off test failed, replace the faulty fuel injector(s). If the high-pressure pump or its integrated Metering Unit (MeUn) is failing to build pressure, replace the fuel pressure regulator/metering unit or the entire high-pressure injection pump assembly.

5. 5

   Final Validation

   Clear the EDC fault codes. Run the tractor under load (using hydraulics over relief or a dynamometer) to ensure rail pressure meets commanded parameters without dropping.