What is the difference between an engine with a mechanical throttle lever and one with an electronic (drive-by-wire) throttle?
On a mechanical throttle a wire links the lever and butterfly; on an electronic one the pedal is only a sensor and the ECU drives it. Cable kits fit the first.
The difference is set by the physical connection between the lever and the throttle. On a mechanical throttle the pedal or lever moves the throttle butterfly, or the injection pump lever, directly through a cable or a rod. On an electronic throttle (drive-by-wire) the pedal is only a position sensor; the butterfly is driven by the engine's ECU through a separate motor. Since the GS740 family rides on top of the mechanical line, it suits only the first group.
The two systems side by side
| Comparison | Mechanical throttle | Electronic throttle |
|---|---|---|
| Between lever and butterfly | An unbroken wire or rod | An electrical signal |
| What sets the fuel quantity | The position of the lever | The ECU |
| Supervision in between | None | Faulty signal supervision, idle control, emission strategies |
| Typical problem | Friction and hysteresis in the Bowden cable | A fault record from the sensor or the ECU |
| Suitability for a cable-pull kit | Suitable | Not suitable |
On the mechanical side the route matters: friction and hysteresis can build up in a Bowden cable, which is why sharp bends are avoided. On the electronic side the pedal generally carries a dual-channel position sensor; the ECU compares the two channels and counts any inconsistency as a fault.
The method of fault finding parts company for the same reason. On a mechanical system the places to look are known: the friction inside the sheath, the adjusting nut at the end of the sheath and the return spring of the lever. On an electronic system the counterpart of the same complaint is a fault record, and the intervention is made with an instrument rather than with a mechanical tool.
How to tell which one your engine has
- With the engine stopped, move the throttle lever or the pedal by hand. If the lever on the injection pump or on the carburettor moves with it, the system is mechanical.
- If there is a visible wire or rod running from the end of the lever to the pump, it is mechanical.
- If there is a multi-wire connector on the pedal and no moving mechanical connection on the pump side, the system is electronic.
- If you hear or see the throttle butterfly moving of its own accord when you switch the ignition on, there is a separate motor driving the butterfly; that is an electronic throttle.
- If you cannot be sure, look at the compatibility list under which engines the kit fits.
The kit does not take the place of the governor
One more important distinction: even though the kit makes a mechanical throttle electronic, it does not take the place of the governor of the engine. The mechanical governor stays on the engine and it is the governor that regulates the fuel as the load changes. The kit only says where the lever will stop. The closed loop on the GS740-3P is not over engine speed either, but over actuator position; an AS5600 magnetic encoder measures the angle of the servo shaft and settles it at the commanded position. The practical consequences of that distinction are set out in detail under whether the kit takes the place of the governor and the difference between open loop and closed loop.
What is not done on an engine with an electronic throttle
The GS740 and the GS740-3P take the lever to the position you want by pulling a cable; on an engine with an electronic throttle there is no mechanical lever to pull, so there is no work for them to do. Intervening in the pedal signal is a separate matter: the ECU supervises the dual-channel sensor continuously, a signal supplied from outside produces an inconsistency and the engine drops into limp mode. On engines of that kind the answer is a system that works at signal level and fits the structure the ECU expects — not a cable-pull kit.
One check is enough for the decision: if you see a lever moving mechanically on the engine when you move the throttle control, the kit can be applied. If you do not, it cannot; settle which group the engine falls into before looking for an intermediate solution.
The full topic: Electronic speed and throttle control on diesel engines