Common Faults & Maintenance Guide for Diesel Generator Sets

Common Faults & Maintenance Guide for Diesel Generator Sets

When a diesel generator is not operating properly and the self-diagnostic device does not output any fault codes, it is necessary to rely on the operator's inspection and preliminary judgment to determine the nature of the damage and the location of the fault. The common faults of diesel generator sets are summarized as follows:

1. Starting Mechanism Failure Preventing the Diesel Generator from Turning or Turning Too Slowly

• Insufficient battery charge, loose or severely oxidized battery terminal clamps. 
• Blown main circuit fuse.
• Ignition switch failure. 
• Starter motor damage.

Open circuit in the starting wiring or poor connector contact.

2. Fuel Injection System Failure

• No fuel in the tank. 
• Fuel pump not working or low fuel pressure
• Fuel pipe leakage or deformation.
• Open circuit relay.
• Malfunctioning fuel pressure regulator.
• Clogged diesel filter.

3. Intake System Failure

Faulty idle control valve or its control circuit.

Cracked idle control valve air pipe or leaking connector.

Airflow meter malfunction.

4. Unstable Speed Failure

(1) Fault Phenomenon

When the diesel generator is operating, the speed fluctuates between high and low. This condition is referred to as engine stalling, and the fault is called engine stalling failure.

• Causes:
  The reasons for unstable engine speed include faults in the fuel injection system, ignition control system, and intake system. Common causes include:
• Air leaks in the intake system (e.g., loose hoses, PVC valve leaks, EGR system leaks, oil dipstick port leaks, oil filter cap leaks). 
• Unstable fuel supply pressure (e.g., deformed fuel pipes, poor wiring connections, insufficient fuel pump pressure, unstable fuel pressure regulator, clogged diesel filter, relay contact flickering).

Troubleshooting Methods:

Check for air leaks in the intake system (inspect hoses, PVC valve pipe, EGR system, oil dipstick port, oil filter cap).

Inspect fuel supply pressure (check fuel level in the tank, fuel line pressure stability). The method is similar to diagnosing engine starting difficulties.

(2) Fault Condition

When the diesel engine operates normally at medium to high speeds but experiences unstable idle or even stalls at low or near-idle speeds, this is referred to as an idle speed malfunction.

Causes:
Idle speed issues are usually caused by problems in the intake system or fuel injection control system, though mechanical faults can also contribute.

(3) Common Causes of Idle Speed Malfunction

• Fault Condition: Unstable engine speed, noticeable power loss, and backfiring may indicate an overly lean fuel mixture.
• Fault Phenomenon: The engine operates normally when accelerating slowly from low to high speed, but during rapid acceleration, the speed changes sluggishly, sometimes with choking or backfiring.

Maintenance Guidelines

The diesel injection system has high requirements for fuel cleanliness. Always use diesel with the correct specifications and quality. Replace the diesel filter regularly to prevent clogging of the injectors.

If the battery is too weak to start the engine, recharge or replace it instead of using jump-start methods.

Do not wash the electronic control unit (ECU) or other electronic components with water. Avoid high-humidity storage environments, and refrain from washing the floor with water in summer.

When the ignition switch is turned on (without starting the engine), the warning light should illuminate. If it remains on after normal startup, the ECU has detected a fault. Do not disconnect the battery at this time to avoid losing stored fault codes. Use diagnostic tools to read the fault codes based on the warning light flashes.

Before inspecting the fuel system, disconnect the battery ground cable.

The electric fuel pump is controlled not only by the ignition switch but also by a switch in the airflow meter. The pump operates only when the engine is running or starting, and the airflow meter detects airflow or the ECU receives speed and ignition signals.

Caution: Never disconnect any electrical device while it is operating, whether the engine is running or the ignition is on. Sudden disconnection can generate high voltage spikes, damaging electronic components.

If arc welding is required, disconnect the ECU power supply first.

When inspecting the ECU or connected sensors/actuators, operators must discharge static electricity by wearing a grounded wrist strap to prevent damage to electronic components.