Case IH 19713 – Engine Control Unit (ECU): Fuel Metering Unit : maximum rail pressure exceeded - overrun detection

The Engine Control Unit (ECU) has detected that the fuel pressure inside the common rail has exceeded the maximum allowable limit during an 'overrun' state (e.g., decelerating, coasting downhill, or suddenly releasing the accelerator). This indicates that fuel is still being forced into the rail or pressure cannot escape, pointing to a mechanical failure in the fuel metering unit, a stuck-closed pressure relief valve (PRV), or a skewed rail pressure sensor.

• Tier 4b
• Case N-Series Tractor Loader Backhoes (TLBs)
• Case IH Magnum series tractors
• Case IH Puma series tractors
• Case IH Maxxum series tractors
• Case IH / New Holland CR series combines

1. 1

   Connect the CNH Electronic Service Tool (EST) and monitor the Actual Rail Pressure versus the Desired Rail Pressure during a simulated overrun condition.

2. 2

   Check the wiring harness and connectors between the ECU and the Fuel Metering Unit (M-Prop) for short circuits, open circuits, or loose contacts.

3. 3

   Check the Rail Pressure Sensor raw voltage/value to verify if it reads high pressure even when the engine is off and the system is depressurized.

4. 4

   Inspect the Pressure Relief Valve (PRV) on the fuel rail to ensure it is not stuck closed.

5. 5

   Test the Fuel Metering Unit on the high-pressure fuel pump for sticking or binding.

1. 1

   Depressurize the System

   Ensure the engine is off and allow the high-pressure fuel system to depressurize and cool down before opening any lines.

2. 2

   Repair Wiring

   If diagnostic checks revealed chafed wires or loose pins at the Fuel Metering Unit connector, repair the harness and retest.

3. 3

   Replace the Fuel Metering Unit

   If the wiring is intact but the rail pressure spikes during overrun, the Fuel Metering Unit (M-Prop) on the high-pressure pump is likely sticking. Remove the unit from the high-pressure pump, clean the mounting surface, and install a new metering unit.

4. 4

   Replace the Rail Pressure Sensor

   If the sensor was found to be reporting skewed data during the diagnostic phase, replace the sensor located on the common rail.

5. 5

   Clear and Retest

   Use the CNH EST to clear the fault codes. Test drive the machine, intentionally simulating an overrun condition to verify that the actual rail pressure drops to match the desired rail pressure and the code does not return.