Diesel Generator Fuel Pump Failure: Diagnosis & Solution Guide

A malfunctioning fuel pump is a common cause of diesel generator starting failure or power loss. At EMEAN POWER, our engineers employ a systematic diagnostic approach to accurately determine if the fuel pump is the culprit and identify the specific failure mode. Follow this professional procedure to diagnose the issue.

Professional Diagnostic Procedure:

1. Pre-Check: Ensure Fuel System Integrity
Before testing the pump, verify the integrity of the low-pressure fuel circuit.

• Check: Ensure all fuel lines from the tank to the injection pump are intact, unobstructed, and free from air leaks. The system must be properly bled of air.

2. Direct Fuel Pump Output Test
This is the definitive test for the lift/supply pump's function.

• Step 1: Locate and carefully loosen the bleed screw or a fuel line connection on the inlet side of the fuel injection pump.

• Step 2: Crank or start the diesel generator.

• Step 3: Observe the fuel flow at the loosened connection.

  • Normal Result: A strong, steady, and air-free stream of diesel fuel indicates the fuel pump is operating correctly. Pressure and volume are sufficient.

  • Abnormal Result: No fuel, a weak trickle, or a flow heavily mixed with air bubbles indicates a failing pump, a severe blockage upstream, or persistent air intrusion.

3. Differentiating Between Pump Failure and Other Issues
If the pump test fails, further isolate the cause:

• Electrical Fault (for electric pumps): Check for proper voltage at the pump terminals during cranking.

• Mechanical Fault (for engine-driven pumps): Inspect the pump drive coupling or gear for damage.

• Internal Failure: Worn internal components, a damaged diaphragm, or faulty check valves within the pump itself.

EMEAN POWER Recommendation: A fuel pump showing weak or no output typically requires replacement. Continuing to operate with a failing pump can lead to injection pump damage due to fuel starvation. 

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