Speed Test Under Load
This is verifying the settings with the real working load rather than unloaded. A throttle position found unloaded does not give the same speed when load is applied; even though the engine's mechanical governor increases the fuel, the speed drops somewhat. The test measures this drop and shows that the operating point is still in an acceptable range.
The method of the test is simple. Bring the engine to the stored or selected work position and read the unloaded speed with a tachometer. Then bring in the real load — start the pump discharging, start the machine working — and read the speed again. The difference between the two values is that engine's droop behaviour at that load.
Interpret the result as follows:
- If the drop is small and the working speed is still on target, the setting is suitable.
- If the drop is larger than expected, the engine may be running at its limit for that load; the fuel system, the air filter and the load must be evaluated.
- If the speed oscillates, continuously going up and down, look for mechanical sticking or a problem on the governor side.
This is why the adjustment is made under load: a position-based system cannot see the effect of the load. The GS740 and GS740-3P drive the position of the throttle lever; holding the speed independently of the load only comes into play with the optional feedback module that measures speed.
Context in which this term is used: Electronic speed and throttle control on diesel engines