In the UK, you could get a Ralliart injector driver module to raise the power from 134 to 167 bhp and this was fitted by Mitsubishi UK. Check to see if you have one of those or any other similar 'performance module' and if so, remove it and see what happens then.
Most aftermarket ones just plug into the sensor at the end of the common rail. From descriptions of other forum users, the Ralliart one is housed next to the battery.
Not sure what I'm looking at o be honest does anyone have a photo ? the pickup was originally a German import into Greece if that makes any difference.