Help! Engine pinging only 140,000 miles

[dustbustet707]

I have a 2003 mustang V6. I noticed opinion in the engine a couple months back I've been babying it and it's still there even though I tried premium gas octane booster everything I can think of I replace the PCV valve I replace the fuel filter. I took it to the shop and they said that they're not quite sure they think it might be valve play might be this it might be that the only thing I really heard was $8,000 and I was like oh probably not. So my friend said something about a timing chain but the shop said that the timing is controlled by the computer and that is probably valve play. I don't know if they just wanted the couple hundred dollars to diagnose it or what was the deal but I need some help please please please any ideas anybody

 

[Bullitt347]

The ignition timing is controlled by the computer.
The cam is driven by a timing chain and gears.
It the timing chain is stretched, the camshaft will be retarded from where it should be.
The computer will not know that this has happened.
Excessive carbon build up in the combustion chamber and on top of the piston's can cause a hot spot that can contribute to detonation/pinging.
What do the spark plugs look like?