Case IH 3922 – Engine Control Module (ECM) / EDC (Electronic Diesel Control): Fuel pressure control Metering unit: Fuel rail pressure below limit with MeUn Control with empty tank

A fuel starvation issue where the actual pressure in the high-pressure fuel rail has dropped below the minimum acceptable limit. The Fuel Metering Unit (MeUn) is commanding more fuel to raise the pressure, but the system is unable to achieve it, suspecting a lack of fuel supply from the low-pressure side.

• Case IH agricultural and construction equipment with FPT Tier 3 and Tier 4a engines

1. 1

   Verify the fuel tank is not empty or critically low, causing the pickup tube to draw air.

2. 2

   Visually inspect the fuel tank, bottom/sidewalls, and fuel lines for damage. Ensure the fuel tank vent is not clogged.

3. 3

   Check for air ingress by installing a clear test line between the primary filter and the inlet of the fuel lift pump. Run the engine and observe for air bubbles.

4. 4

   Measure fuel inlet restriction with a vacuum gauge on the inlet of the fuel lift pump (should not exceed 50.8 mm / 2 inches Hg under full load).

5. 5

   Measure low-pressure fuel supply with a pressure gauge between the secondary fuel filter and the high-pressure pump inlet (minimum 5 bar / 72 psi; dropping below 0.276 bar / 4.0 psi indicates failure).

6. 6

   Inspect all Voss O-ring fittings on the fuel lines for potential air leaks.

1. 1

   Refuel and Prime

   If the tank was empty, fill the fuel tank and properly prime/bleed the fuel system to remove all air.

2. 2

   Replace Filters

   If fuel inlet restriction is high, replace the primary fuel filter (water separator) and the secondary fuel filter. Clean the fuel tank if heavy debris or algae is found.

3. 3

   Seal Air Leaks

   If air was observed in the clear test line, replace the Voss O-ring fittings and/or damaged low-pressure fuel lines from the tank to the lift pump.

4. 4

   Replace Lift Pump

   If there is no air in the system and no restriction, but low-pressure supply to the high-pressure pump is still below spec, replace the mechanical gear pump (lift pump).

5. 5

   Address High-Pressure Components

   If the low-pressure fuel supply is perfectly within spec (good pressure, no air), test the Fuel Metering Unit (MeUn) on the Bosch high-pressure pump, check the fuel rail pressure relief valve (PRV) for bypassing, and check the injectors for excessive return leakage.

6. 6

   Verify Repair

   Clear the EDC fault codes using a diagnostic tool. Run the machine under a heavy load (e.g., hydrostatic stall, converter stall, or dynamometer) to rated RPM to ensure the fuel rail pressure maintains the commanded limit without dropping.