Been trying to resolve an issue, hopefully someone can help. Noticing under wot in the higher range around 6k+ the needle on the tach begins bouncing all over the place, 500 rpm or so each way. When logged with the datalogit, the chart shows the same result. First I thought it was an average gauge cluster issue before I noticed the datalogit shows a similar trend. Any idea what might cause this? Could it be an issue with the cas, or perhaps the fact that the cas wiring is non factory and possibly non shielded? Any input is appreciated, thanks.

 

Could be radio interference when the coils are working harder.

Possibly enough slop developed somewhere for CAS to trigger wheel offset issues but I'd think you'd lock the engine up or notice other problems if the crank was wondering that much. Worth checking the sensor is physically secure and wiring isn't rubbed through.