said by matt5:
If you are having issues with pinging, you likely have other issues, and should get them looked at asap as pinging will destroy the motor in a short time.
I would agree. This car shouldn't knock on regular. It sounds like the ECM is putting out bad timing curves. It was suggested it may have a lot of deposits, but it would have to have a lot of blow-by from the rings or valves generally speaking.
One thing the op can do is pull a middle plug, and check for pre-ignition damage to it. It'll look melted/ corroded.
Is the engine running hotter than normal? That's also a sign...