The speed keeps going up and down; what can cause hunting?
Hunting is the engine's inability to hold fuel and throttle position steady. The most common causes are mechanical binding in the actuator or linkage, a governor sized wrongly for the engine, unstable supply voltage, a faulty speed signal, and incorrect droop or gain settings. If the gain is high there is oscillation, if it is low there is a late response; the rule is to sharpen it until oscillation begins and then back it off a little.
With oscillation, rule out the mechanical side first:
- Friction and binding: a sharply curved cable route, a seized joint, or a kinked outer sheath. Friction creates hysteresis, the system overshoots the target and comes back.
- Loose connection: a moving terminal or bracket leaves play between the command and the actual position.
- Supply: a weak battery, a loose chassis connection, or a cable of insufficient cross-section causes voltage drop as the actuator moves.
The GS740-3P's soft ramp exists exactly to reduce this oscillation risk: it applies the position command as a ramp instead of a step. If oscillation still continues, its source is outside the kit; the engine's own mechanical governor is responsible for speed regulation, and its setting or condition must be examined. Remember, these kits do not replace the governor; speed regulation is done by the engine's own system.
Full topic: Electronic speed and throttle control on a diesel engine