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.
BagusJeep lives in Bali.
1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE