New Holland ENG 3906 – Engine Control Unit (ECU): Injector: Number of injections is limited by quantity balance of high pressure pump

The Engine Control Unit (ECU) monitors the requested number of fuel injections against the current capability of the fuel injection system to fulfill that request. This code triggers when the high-pressure fuel pump cannot supply enough fuel volume to maintain the required rail pressure for the requested injection events. To prevent stalling or severe pressure drops, the system limits the number of injections. This generally points to a fuel supply restriction, a failing high-pressure pump, a faulty fuel metering unit, or a massive pressure leak.

• WorkMaster 50
• T9 Series
• T9.480
• T9.530
• T9.560
• T6 Series
• T7 Series
• T8 Series
• Magnum series
• CR8.90
• CR9.90
• CR9090
• CX8080
• CX8090
• W50C
• W60C
• W70C
• W80C
• 21F
• 121F
• 221F
• 321F

1. 1

   Battery and Voltage Check: Ensure battery voltage is sufficient. Low voltage can cause erratic ECU behavior and limit power stages to the fuel metering unit.

2. 2

   Low-Pressure Fuel System: Check the fuel level and inspect for contaminated fuel (water in fuel). Inspect the low-pressure lines for air leaks, kinks, or restrictions.

3. 3

   Fuel Filters: Check the primary fuel filter/water separator and secondary fuel filters for clogging, which is the most common cause of fuel volume starvation.

4. 4

   Wiring and Harnesses: Visually inspect the relevant harnesses and connectors for damage, bent/dislocated pins, or loose contacts between the Fuel Metering Unit (MeUn) and the ECU (often associated with related code 3910).

5. 5

   Pressure Relief Valve (PRV): Check if the PRV on the fuel rail is stuck open or leaking (often accompanied by codes 3915 or 3916).

6. 6

   Injector Return Flow: Check the injectors for excessive return flow, which can bleed off the pressure the pump is trying to build.

1. 1

   Read and Verify Codes

   Connect the EST (Electronic Service Tool) or use the diagnostic lamp blink codes to verify ENG 3906 is active. Look for accompanying codes (like 3910 for the metering unit or 3915 for the PRV) to narrow down the root cause.

2. 2

   Resolve Low-Pressure Issues

   Replace the fuel filters and water separator. Bleed the fuel system using the fuel priming pump to ensure no air is trapped in the lines.

3. 3

   Harness Repair

   If diagnostic tests reveal high resistance or an open/short circuit in the fuel metering unit wiring, repair or replace the harness as required.

4. 4

   Component Replacement

   If the low-pressure system and wiring are intact, the fault lies in the high-pressure system. Replace the Fuel Metering Unit (M-Prop) on the pump. If the issue persists, the High-Pressure Fuel Pump itself is failing to balance the fuel quantity and must be replaced.

5. 5

   ECU Re-initialization

   If the ECU or major injection components are replaced, use the EST service tool to re-initialize the ECU and load the appropriate data-set for the engine type (this may require an authorization code from CNH TSS).

6. 6

   Clear and Retest

   Clear the fault codes and run the machine under load to confirm the elimination of the fault.