The speed drops when the engine is strained under load — how do I prevent this?
The drop in speed when load is applied is called droop and is normal on engines with a mechanical governor; typically the no-load speed is 2-3 Hz higher than the full-load speed. A kit that drives the throttle position does not eliminate this, because it does not measure how fast the engine is turning. To zero out the droop, feedback that reads the speed is needed, that is, an isochronous governor.
First separate the mechanisms:
- Normal droop: a mechanical governor works with a balance of spring and weights and cannot produce zero droop. This is not a fault; on generators running in parallel it is even what provides load sharing.
- Excessive drop: a blocked fuel filter, air ingress, an injector problem, an incorrectly adjusted governor or an oversized load. Resolve these first.
The GS740 and GS740-3P are not a governor; they drive the position of the throttle lever, and the mechanical governor stays on the engine. If the load increases while the position is fixed, the speed still drops.
Ways forward:
- Size the load correctly for the engine capacity; do not run continuously very close to full load.
- Set the operating point somewhat higher so that, after the drop when load is applied, the speed stays in an acceptable range.
- If the speed really must stay constant, consider the optional active-feedback speed-holding module for the GS740, that is, the sensor that reads engine speed.
Full topic: Electronic speed and throttle control on diesel engines