I also experience a "tapping", "pinging" sounds when accelerating. I've read from old threads that this is normal for a short pinging to occur during acceleration, but mine keeps pinging until I stop accelerating. I use 89 fuel and the truck was just serviced.

How do you guys know it's the valves and not the pistons slapping against the side of the cylinder from a worn out engine? I have 45k on mine. I guess I wanted to know how to distinguish the sound from a valve from a sound from some other part of the engine.

Thanks