Answer
A frequency fluctuation means the generator RPM is swinging between approximately 1140 RPM and 1200 RPM (for a 4-pole machine). This points directly to a governor or fuel delivery anomaly.
Governor Mechanical & Hydraulic Integrity: Check the oil level and condition inside the hydraulic governor (e.g., Woodward governor). Contaminated or incorrect viscosity oil causes sluggish compensation. Check for mechanical play or binding in the governor output linkage to the fuel injection racks.
Fuel System Air Ingress: Inspect for air bubbles or micro-leakages in the fuel supply/return lines. Air pockets inside the fuel rail cause intermittent fuel starvation across cylinders, making the engine hunt.
Electronic Governor Setup: If fitted with an electronic governor, check the Actuator magnetic pickup sensor for accumulated debris or incorrect clearance from the flywheel teeth. Adjust the Gain and Stability settings on the governor control panel.
Electrical Load Dynamics: Verify if a large cyclic load on deck (e.g., a faulty crane or heavy ventilation fan) is cutting in and out rapidly, creating erratic load steps.