Timing reduction with no changes

[Mirageman]

Up till recently my logger has been reading 16* to 22* with 0 to 8 knock sum. Now with no changes - boost, air temp, water temp etc. I am logging 12* to 17* with the same KS. The power seems less also. What gives? It has a '90 ECU and 18# boost. Any ideas?

 

[kpt4321]

Something changed.

Could be the coolant temp, airflow, "octane" value...