Case IH 3906 – Engine ECU (EDC): Injector: Number of injections is limited by quantity balance of high pressure pump.

The Engine Control Unit (ECU) has detected that the high-pressure fuel pump cannot supply enough fuel volume to maintain the required common rail pressure for the demanded number of injections. To prevent the engine from stalling or the rail pressure from dropping below critical operating levels, the ECU intervenes by limiting the number of injections (e.g., cutting out post-injections or limiting the main injection quantity) to maintain a safe fuel quantity balance.

• Farmall
• Maxxum
• Magnum
• Steiger
• Case construction loaders
• Case excavators

1. 1

   Inspect the low-pressure side for restrictions. Check for clogged fuel filters, a failing lift pump, or air intrusion in the fuel lines.

2. 2

   Visually inspect the fuel rail, injector lines, and high-pressure pump fittings for external leaks.

3. 3

   Check the Pressure Relief Valve (PRV) on the fuel rail. If it is leaking fuel back to the return line or popping open prematurely, it will bleed off rail pressure.

4. 4

   Perform a return flow (leak-off) test on the fuel injectors. Worn injectors with excessive return flow will deplete the rail pressure faster than the pump can supply it.

5. 5

   Inspect the wiring and connector to the fuel metering unit on the high-pressure pump for loose contacts.

6. 6

   Use the CNH Electronic Service Tool (EST) to perform a high-pressure pump quantity balance/flow test to confirm if the pump itself has failed internally.

1. 1

   Resolve Low-Pressure Issues

   Replace the primary and secondary fuel filters. Bleed the fuel system to ensure no air is trapped. Clear the code and test run the machine under load.

2. 2

   Address Leaks

   If the PRV is leaking during normal operation, replace the Pressure Relief Valve.

3. 3

   Replace Faulty Injectors

   If the leak-off test reveals excessive return flow from one or more injectors, replace the faulty injectors. Ensure you program the new IMA (Injector Adjustment) codes into the ECU using the service tool.

4. 4

   Replace Fuel Metering Unit

   If diagnostics point to a sticking or electrically faulty metering unit, replace the valve (often available separately from the pump).

5. 5

   Replace High-Pressure Fuel Pump

   If all filters are clean, lift pump pressure is in spec, injectors are not leaking, and the PRV is holding, the high-pressure pump is worn out. Remove the pump gear/drive, unbolt the pump assembly, and install a new or remanufactured high-pressure fuel pump.

6. 6

   Calibration

   After replacing the EDC, pump, or injectors, use the CNH EST to clear fault codes and restore self-learning parameters.