My 1989 300TE recently developed an annoying ping.
It happened under hard accelaration and when the engine was hot.
I did a search here and decidced to try some Techron Concentrated Cleaner.
I am happy to report that the stuff works as advertised.
After the first treatment I took my car up a long, steep highway grade near my house. When I stepped on the gas a puff of black smoke went out the pipe...(almost looked like a diesel).
After that the car ran much better. After a few more tankfuls I repeated the treatment again.
Now the car runs perfectly...no ping, no knock.
That stuff really works.
One suggestion though. Be sure to change the oil after you use Techron. Before the treatment my car's oil had a nice, rich golden color. After the treatment the oil had a darkish, dirty look.
So I changed the oil and filter.