Generator Surging

Okay I'm new to online help forums so I apologize if I make any silly etiquette mistakes ahead of time. I'm not looking for a direct answer but more so guidance on the steps I take to solve the issue/my thought process to troubleshoot this.

The engine is a cummins PCC2100 DSHAA 150kw and it had between 30 - 45 kW .88 pf with one phase switching between .91 leading and lagging quite quickly with a quick fluctuating load.

Today during a power outage we had a generator that was surging/hunting under load. I only noticed this because one of our UPS was sending a phase synchronization alarm to my email. When I opened the ISX client I saw that the generator was outputting 59.85hz. So I went to investigate.

What I found is the engine RPM was fluctuating between 1780 and 1810 and the freq was outputting 59.5 - 60.6hz according to the display. I inspected for fuel leaks or possible loose connections where air can get in and everything visually checked out. Without any tools or much time to sort this out I went into the setup and adjusted the AVR/Governor by turning the gain down to 50% from 100% and left the regulator alone bc the voltage was displayed as stable.

The result was a smaller window of fluctuation 1792 - 1801 RPM and 59.8-60.1 Hz. I am not happy about how unstable the RPM is but it was good enough to supply the load without worry and it stopped the phase sync issue for the UPS.

Once power was restored I ran the generator at idle and it was a stable 1800 RPM so I set the governor gain back to default of 100% and observed the stable 1800 RPM as well.

The load is fairly small so I can't see it posing an issue for our governor/AVR but I will quickly rule this out by attaching a resistive load bank and applying 30/40 kW to see how the generator responds and if it responds well at a multitude of loads I will apply the load bank on top of the building load to observe the pattern again.

What I suspect is a fuel restriction issue or air getting into the high pressure lines.

I don't have INSITE, quickserve or any of the speciality tools that are listed in the repair manual, but I will be getting an account and software in a week or so.

Once I have INSITE and can control the idle speed and hopefully the ability to pressurize the rail, cut cylnders etc. I plan to do the following.

Connect a fuel line to the quick connect outlet of the fuel filter and monitor for bubbles in a 5 gallon jug at low idle and then high idle. Look for any other quick connects in the system on the high side and perform the same test.

if all checks out measure the pressure going into the pump and out of the pump.

if that checks out test the fuel injectors with the software by monitoring the fuel they reject into a measuring cup within 20-45 seconds what ever the manual says.

What do you guys think am I missing anything or jumping into anything too quickly?