error messages with an ECU chip would also include something along the line of a torque limit exceeded. If you have ecu'd, there are a few bmw people at a few garages that will bypass the mod. You just have to know who to talk to
If it is the fuel, (and im going out on a limb here) the filter or something(not to sure) might have had a build up of carbon(?) which could cause the HPFP to have problems