1997 F-150 4.2 4x4 257,000 kms

My truck has just in the last few weeks started pinging quite badly while accelerating. It is fine while at highway speed, just getting up to speed. I have tried high octane fuel, different brand of fuel. Nothing has helped. Just started for no reason one day. Reminds me of the old days when the timing was too far advanced and you just backed off the distributor a bit. With the amount of miles on the engine, is this something that will eventually be terminal such as a timing chain that is stretched so badly that it is allowing the valves to hit the piston. I don't plan on putting a lot of money in to it due to the mileage. What could it be and what can I do to fix it if at all possible?

 

hi, i will be worth looking in the 4,2 forum as this is being reviewed on the first page. bokker.