Case IH 3923 – Engine Control Unit (ECU) / EDC: Fuel pressure control Metering unit: Fuel Rail pressure above maximum limit with MeUn Control with empty tank

Fuel rail pressure has exceeded the maximum allowable limit while being controlled by the Fuel Metering Unit (MeUn / M-Prop), specifically under conditions where the system detects or simulates an empty tank scenario. This is typically caused by a mechanical failure of the metering unit, a faulty rail pressure sensor, or severe air ingress/restriction in the low-pressure fuel supply.

• Magnum series (245, 275, 305, 335)
• Steiger series (280, 330, 335)
• Farmall series (90C, 100C, 110A, 120U, etc.)
• Maxxum series (110, 115, 125, 140)
• MX series
• Wheel Loaders (621E/F/G, 721E/F/G)

1. 1

   Check for air ingress by installing a clear test line at the inlet of the high-pressure pump (large amounts of air indicate a leak).

2. 2

   Check low-pressure fuel supply with a pressure gauge between the fuel filter and high-pressure pump (minimum 5 bar/72 psi; drops below 4.0 psi indicate severe restriction).

3. 3

   Inspect fuel pre-filter, main fuel filter(s), and Voss o-ring fittings for leaks or blockages.

4. 4

   Inspect the bottom and sidewalls of the fuel tank for debris blocking the pickup tube.

5. 5

   Test the M-Prop (Metering Unit) wiring harness for loose contacts or shorts to battery/ground.

1. 1

   Resolve Low-Pressure Issues

   If the diagnostic checks reveal low fuel pressure or air in the clear test line, replace the fuel filters and pre-filters. Clean the fuel tank and replace any damaged Voss o-rings on the fuel lines.

2. 2

   Bleed the System

   After replacing filters or fixing air leaks, prime and bleed the low-pressure fuel system.

3. 3

   Replace the Fuel Metering Unit (M-Prop)

   If the low-pressure supply is a steady 72 psi and no air is present, the M-Prop valve on the high-pressure pump is likely sticking, causing the over-pressure condition. Remove the old metering unit from the high-pressure pump and install the replacement.

4. 4

   Replace the Fuel Rail Pressure Sensor

   If the M-Prop is functioning correctly but the ECU is still reading an over-pressure fault, the rail pressure sensor is likely providing a false reading. Relieve system pressure, remove the sensor from the fuel rail, and install the new sensor.

5. 5

   Clear Codes

   Cycle the key and use a diagnostic tool to clear the inactive faults from the EDC.