Genset runs 15-20 minutes

[steve77]

We have a Loadmaster 8 kW genset with a Yanmar 3GMFL-G1 engine. My issue is with the engine not running steadily for periods longer than 15 to 20 minutes.

The engine starts easily and runs smoothly for 15 to 20 minutes, and then will randomly lug down. This results in black smoke and a knocking sound from the engine. The lugging will last for a few seconds and the engine speed will then recover. It will lug down again after a few minutes. If I allow this process to continue, the interval steadily decreases between normal running and lugging.

If I shut the engine off and wait a couple of hours, the process repeats. I can only get 15-20 minutes of genset run time before I have to shut it off.

I have tried shutting off some of the AC loads, but this does not help. The loads that I'm running are a battery charger and a water heater, so there is no cycling of the loads. The water heater takes more than 20 minutes to reach the set point and shut off, so it is steady state during the period that I'm seeing this problem. I have even tried shutting off ALL AC loads, but the engine still lugs.

From my Yanmar manual, the governor is internal to the engine, and no external linkage moves when the governor operates. The throttle is fixed to run the engine at 1800 rpm for 60 Hz 120 Volt power.

Anyone have any ideas of what can be causing this?

Cheers!

Steve

[skipperpete]

Hi Steve. My first thought was a fuel supply problem because on a generator a fall in horsepower (or an increase in load) is always automatically countered by an increase in fuel by the constant speed governor, often a BIG increase to the maximum fuel stop. The equivalent behavior on a propulsion engine would be a loss in power and then the helmsman pushing the engine control to full power.... then when the air bled out, an increase to max governed rpm requiring a reduction by the helmsman. A small amount of air or a restriction in the fuel supply will cause your generators symptoms, including the knocking........BUT this line of reasoning is less credible when, with all load removed the problem still remains, it should diminish.
Is the voltage constant? If it’s not fuel then the AVR might be on the fritz. Does your generator have capacitors?
Do the usual stuff, change all the fuel filters, check the lift pump, maybe put a length of clear plastic hose between the secondary filter and the injector pump to check for bubbles.
Keep a close watch on the frequency because there is a vague possibility that this problem is related to a sticky injector pump plunger...

[deblen]

Originally Posted by skipperpete

Hi Steve. My first thought was a fuel supply problem because on a generator a fall in horsepower (or an increase in load) is always automatically countered by an increase in fuel by the constant speed governor, often a BIG increase to the maximum fuel stop. The equivalent behavior on a propulsion engine would be a loss in power and then the helmsman pushing the engine control to full power.... then when the air bled out, an increase to max governed rpm requiring a reduction by the helmsman. A small amount of air or a restriction in the fuel supply will cause your generators symptoms, including the knocking........BUT this line of reasoning is less credible when, with all load removed the problem still remains, it should diminish.
Is the voltage constant? If it’s not fuel then the AVR might be on the fritz. Does your generator have capacitors?
Do the usual stuff, change all the fuel filters, check the lift pump, maybe put a length of clear plastic hose between the secondary filter and the injector pump to check for bubbles.
Keep a close watch on the frequency because there is a vague possibility that this problem is related to a sticky injector pump plunger...

Is the fuel tank air vent clean?