pinging, detonation?

[WDoherty]

My 92 sc400 pings (i think) when i mash it hard and it hasn't downshifted yet. Its got 103,000 miles and i was suspecting ignition. Although the records say the wires and plugs were changed in 2001 i'm not sure if they were. I pulled the driver side ignition wire cover and the wires looked good and I tested 1 at 10 omhs, i didn't have enought time to tear it all apart and test them all. Anway, i noticed on the wires that there were the numbers 1991 and the rest with 1992 after the name) which i don't remember. Do these numbers mean the wires were made in 1991 or 1992 or is this pure coincedence. Besides i didn't get down to the problem, what about engine speed sensor, cam sensors, ect., would i be better off having Lexus put it on their diagnostic equipment to verify all sensors and ingition functions. Anyone else have pinging, and yes i do use hi-test fuel. Also, it might idle kind of low once warmed up and in gear. Oh, also, the exhaust has smelled kind of rich since i got the car (2004), although i found 2003 records of the car passing emissions( we don't have emission tests where i live). The car gets 22-24 mpg on highway, and i got 16 in town on the last tank with a lot of quick driving. I think those numbers are average, so i don't know if its rich.