pinging problem at high speeds 02 crown vic lx helpme

very strange problem , engine pinging at highway speeds with air conditioning on foot on throttle , i can let off throttle and noise goes away as soon as i hit the gas again it starts up again! Other than that car runs fine no skips no slack no nothing, no engine light either so i dont have any path to follow. i have done the usuals that go with ford i.e cleaning tbi, egr, iac, replacing sensors you name it , really busting em on this one , any info on this would be interesting to hear. 4.6 with 140,000 on it

Over the years, gasoline has become contaminated with cheaper gasoline. The additives that the name brand gasoline is superior to the cheaper brands. And some of the smaller stores will take whatever they can get cheap.

It is possible you have had minor carbon buildup on your pistons. An old trip we used to use was to rev up the engine and slowly pure water (about 8 oz) into the carb, increasing rpms to prevent the engine from stalling. When we would get near the end, we dumped the last ounce in and let the engine stall. Leave it over night to soak. The next day you could see the crud coating the exhaust pipe on the inside.

Now I have used Seafoam and Chemtool B12 (and there are others) that you can inject into the intake through a vacuum line. https://www.youtube.com/watch?v=zt_oXKxe3wo It seems to work, especially if you don't feel like removing the heads.