I drive a 2007 Jazz VTEC CVT
I recently started getting some strange jerking under load. It usually happens at its worst at around 3500 RPM but also above. As this is where the VTEC usually kicks is I have a feeling it has something to do with the VTEC switchover. Sometimes when this happens the battery light with flash with every jerk. I have had a ODBC code reader on it, but not while the jerking happened, and got no codes. The problem is also worse if there is more load on the electrical system eg. lights on etc. I also hear a buzzing/rattling noise under the dash at the right hand footwell (right hand drive) when the jerking happens. Could this be a grounding problem or some problem with a relay?

 

Woah Sounds Crazy i hope someone helps

 

On a drive on the highway I made sure I had Torque running on my tablet with my wife watching the voltage and other stats during the jerking and battery light flashing. We could clearly see the voltage going to high, above 15V and to low, below 12V. The only think that I can think of that can cause over voltage would be the voltage regulator.
So on the weekend I replaced the alternator. This involved removing the inlet manifold and air filter box to have enough space in front of the engine to get to the alternator. I recommend a small socket set with long and short sockets and different lengths of extensions. Most of the time you use a 10mm and 12mm socket. The old alternator was slightly smaller than the replacement part (#52 on old and #56 on sticker on new one)
Did another drive with Torque on the tablet and the voltage is now much more stable, between 14.1 and 14.4 volt.