Hitachi EX120-5 Stepping Motor Possible Issue

[NikinNZ]

Hello, i have an issue with my Hitachi EX120-5 when moving forward i get about 30 metres then the engine struggles and stalls, same if i use the boom, however i can rev the machine while stationary and it will be fine, someone suggested it may be the stepping motor? do these need computer calibrated once installed? or is it something i can do myself? it may not even be that?

 

[Diesel Dave]

Be sure the engine stop cable below the operator seat is fully pushed inwards.
To eliminate any potential engine speed control issues turn off auto idle.
The stepping motor itself doesn’t generally create any unstable engine speed issues like you are describing. Backprobe the 3 terminal EC sensor to check the sensor output voltage. The middle output wire (yellow/ black tracer] and the outside ground wire (brown/ blue tracer). At high idle with (HP off) the voltage should be approximately 3.50- 3.70v dc.
If the voltage remains stable and consistent when the engine is stalling then you know the stepping motor/circuit is not the issue.

 

[NikinNZ]

Excellent! Thanks Dave i wil give that a go. Much appreciated.