The pinging is detonation and can have several causes, poor fuel and timing are common.
Poor fuel - how old is the fuel? Modern fuel goes stale quite quickly, anything more than 6 months and I would suspect the fuel. A low RON fuel will ping more easily. If it is new and you are using a new source of cheap fuel you may consider changing.
Timing - you have not filled in your Profile so hard to say. IF you have the 258 and the computer still hooked up it may be the computer and its sensors playing up, I understand they are not supposed to ping as the computer will adjust automatically. A Nutter bypass of the sensor wires direct to the ignition ECU rather than through the computer may help.
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