Case IH 3924 – Engine Control Unit (ECU) / EDC: Fuel pressure control Metering unit: Fuel Rail pressure above maximum limit with MeUn Control (second stage) with empty tank

The engine's fuel rail pressure has exceeded the maximum allowable safety limit during the second stage of the Fuel Metering Unit (MeUn) control. This is often caused by a critically low fuel level or air entering the fuel system, which mimics an empty tank condition and causes the metering unit to overcompensate.

• Maxxum series
• Steiger / Quadtrac series
• AFX series combines
• Puma tractors
• Magnum tractors

1. 1

   Verify the fuel tank is not actually empty or critically low, which would draw air into the pickup tube.

2. 2

   Install a clear test line at the inlet of the high-pressure pump and run the engine under load to check for air ingress (a steady stream of bubbles indicates a suction-side leak).

3. 3

   Perform a low-pressure supply test by connecting a pressure gauge between the fuel filter and high-pressure pump (should be minimum 5 bar/72 psi; below 0.276 bar/4.0 psi indicates severe restriction).

4. 4

   Inspect the fuel pre-filter, primary fuel filter, and Voss O-ring fittings for blockages or loose connections.

5. 5

   Inspect the electrical harness and connector at the Fuel Metering Unit (MeUn) on the high-pressure pump for loose contacts or corrosion.

1. 1

   Resolve Low-Pressure/Air Issues

   If air was found in the clear test line, trace the low-pressure lines back to the tank. Replace any damaged Voss O-rings, cracked lines, or clogged fuel filters. Clean the fuel tank if debris is blocking the pickup tube.

2. 2

   Bleed the System

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

3. 3

   Replace the Fuel Metering Unit (MeUn)

   If the low-pressure supply is solid (5 bar/72 psi) and no air is present, the Fuel Metering Unit is likely mechanically sticking. Disconnect the battery, unplug the electrical connector from the metering unit on the back of the Bosch high-pressure fuel pump, remove the mounting screws, and extract the unit. Lubricate the O-rings on the new unit with clean diesel fuel, install, and torque fasteners to OEM specifications.

4. 4

   Clear Codes and Test

   Use the CNH Electronic Service Tool (EST) / EASy tool to clear the 3924 fault code. Run the engine on a dynamometer or under field load to verify that rail pressure tracks the setpoint without spiking.