Case IH 3926 – Engine Control Unit (ECU) / EDC (Electronic Diesel Control): Fuel pressure control Metering unit: Leakage in overrun with empty tank.

The engine control system has detected an unexpected drop in fuel rail pressure during an "overrun" condition (when the engine is decelerating or coasting without throttle input) while the fuel tank is empty or at a critically low level. The system suspects a leak in the high-pressure fuel system, but the condition is heavily tied to fuel starvation or air ingress caused by an empty tank.

• tractors
• combines
• sprayers

1. 1

   Check Fuel Level: Verify the tank has adequate fuel. The most common trigger for this specific code is running the machine out of fuel or operating on a steep incline with a very low tank.

2. 2

   Check for Air Ingress: Install a clear test line with a pressure gauge between the primary filter and the inlet of the high-pressure pump. Run the engine and observe for air bubbles. A steady stream indicates an air leak.

3. 3

   Test Low-Pressure Supply: Verify the lift pump (gear supply pump) is delivering adequate pressure. The pressure should be a minimum of 5 bar (72 psi) under load.

4. 4

   Inspect for Physical Leaks: Check the high-pressure pump, fuel rail, injectors, and the advance piston cover for visible fuel leaks.

5. 5

   Test the Pressure Relief Valve (PRV): Ensure the PRV on the fuel rail is not bypassing fuel prematurely.

1. 1

   Refuel and Bleed

   Fill the fuel tank completely. Bleed the low-pressure and high-pressure fuel systems of all air according to the operator's manual. Clear the fault code and test run the machine to see if the code returns.

2. 2

   Resolve Restrictions

   If the code persists and low fuel pressure was noted during diagnostics, replace the fuel pre-filter and primary fuel filters.

3. 3

   Seal Air Leaks

   If air was observed in the clear test line, inspect all fuel lines from the tank to the pump. Replace any damaged lines and replace the Voss O-ring fittings, which are common culprits for allowing air ingress.

4. 4

   Replace Lift Pump

   If the low-pressure supply remains below 5 bar (72 psi) after filter replacement, replace the fuel lift pump/gear supply pump.

5. 5

   Replace Metering Unit / PRV

   If the low-pressure side is perfect but the high-pressure rail cannot maintain pressure during overrun, replace the Fuel Metering Unit (MeUn) on the high-pressure pump. If the rail's Pressure Relief Valve is leaking fuel back to the return line, replace the PRV.