Case IH 3808 (DTC 3C65) - ECU – ECU: High pressure pump fuel delivery quantity at low idle is too high

The set point of the fuel metering unit in idle mode is not plausible. The engine is detecting that the high-pressure fuel pump is delivering more fuel to the common rail than is commanded at low idle. This is most commonly caused by a sticky, stuck, or failing Fuel Control Actuator (FCA), also known as a Fuel Metering Unit or MPROP.

• MAXXUM T4E
• Puma series tractors
• Magnum series tractors
• Farmall series tractors
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Maxxum series tractors

1. 1

   Check for related codes (e.g., 3810, 3112, or 3805) and diagnose them first, as a faulty fuel rail pressure sensor can cause the ECU to miscalculate fuel delivery.

2. 2

   Check the tractor battery power supply to ensure no external power supply is connected, which can cause voltage irregularities and skew sensor readings.

3. 3

   Perform an FCA unplug test if experiencing hard start or no-start conditions: temporarily unplug the Fuel Control Actuator to default the pump to maximum pressure. If the engine starts, shut it off immediately to prevent over-pressurization, confirming the FCA is the culprit.

1. 1

   Turn off the machine, remove the key, and disconnect the battery to ensure safety and prevent electrical shorts.

   Ensure safety and prevent electrical shorts.

2. 2

   Locate the high-pressure fuel injection pump (typically a Bosch CP3 style pump) on the engine block.

   Typically a Bosch CP3 style pump.

3. 3

   Locate the Fuel Control Actuator (FCA / MPROP) mounted on the back or side of the high-pressure pump.

   Mounted on the back or side of the high-pressure pump.

4. 4

   Disconnect the electrical wiring harness connector from the FCA.

   Disconnect the electrical wiring harness connector.

5. 5

   Remove the mounting screws (usually Torx) securing the FCA to the high-pressure fuel pump.

   Usually Torx screws.

6. 6

   Carefully twist and pull the FCA out of the pump housing.

   Twist and pull the FCA out.

7. 7

   Lubricate the O-rings on the new FCA with clean diesel fuel to prevent tearing during installation.

   Prevent tearing during installation.

8. 8

   Insert the new FCA into the pump housing, install the mounting screws, and torque them to the manufacturer's specification.

   Torque to the manufacturer's specification.

9. 9

   Reconnect the electrical wiring harness.

   Reconnect the electrical wiring harness.

10. 10

    Reconnect the battery, clear the fault codes using an Electronic Service Tool (EST), and run the engine to verify that rail pressure at low idle is now within the plausible range.

    Verify that rail pressure at low idle is now within the plausible range.