What's your Apexi module reading versus the repaired speedo mate? The speed sensor is in the gearbox. Changing diffs and even tyre sizes will change the indicated speeds versus actual speeds but the indicated data that shows up on a factory speedo or an aftermarket monitor via OBD all comes from the same sensor.
Double check that. A 10% discrepancy from the Apexi display seems excessive. Is there a stretch of highway with a Radar speed checker near where you live?
The apexi is reading the same as the speedo. I'm checking the speed with two different gps speed readers. And its also quite clear I'm 10klms slower than the rest of the traffic when the speedo says I'm doing the speed limit.
Thanks for all the info, I just bought my Z back after 7 years… it’s come home with missing parts and all sorts of issues… including the speedo not working, It looks exactly like yours.
I just bought a new cluster to fix this problem. tempted to send it to Otto instruments to get them to refurbish the old one and the replacement one aswell.