You may have hit the proverbial nail on the head with the fouled injector. Try swapping injectors from one side of the engine to the other, and see if the ping follows the injectors. It would also be a good time to inspect the injector inlets for dirt/debris. The 65 psi could have damaged the fuel filter, enough to cause the filter element to start to come apart. Just a thought. Have you ever had the timing belt off? The driver's side cam can be tricky to time correctly, and a cam that's one tooth off will cause some pretty bad spark knocking, but won't be far enough off to bend valves.