GM sells "top engine cleaner" over the counter.
It's used the same way I described using the ATF.
Gm has a few service bulletins for different symptoms that outline this procedure. Symptoms range from engine miss, ping,to carbon knock. But, with the modern fuel injected engines, the cleaner is introduced/ingested through the pcv system. The water part is tricky. I don't feel comfortable describing it in print. It was something an oldtimer physically showed me. It's better to see it done in person. It does work well though.
