Premium fuel!! Does anyone have any ideas why my engine needs premium fuel? If I burn 87 or 89 octane the engine pings. I have had it tuned several times and mentioned it to the shop to no avail. Tey all claim the egr valve is fine. Help!

 

Its possible you have some carbon buildup on the tops of the pistons ? I notice my 300 seems to knock if under load when its hot outside (90+F) If I use 92 octane the problem disappears . The knock is not bad with my engine , just enough to notice . I occasionally run some Marvel Mystery Oil Fuel System Treatment , It seems to help reduce the knocking .