I have a 1994 f150 2x4 ext. cab short bed w/ the 4.9l. it was manufactured 12/93 if that means anything to anyone. there is a noise coming from the engine when it is under load, i want to say its a knocking noise but its not quite, almost a diesely noise. it is not present when cruising, you have to be accelerating or under load, sometimes you are able to hear it at idle but barely. my guess is that it might be a collapsed hydraulic lifter or a small chance its an exhaust leak although i doubt it. i have a video which you can hear it if you have good speakers or headphones.

 

Spark knock? Didn't listen/watch video but your description is typical spark knock. Slight noise at idle could be a secondary noise.

 

i cant tell but did have a clicking in my motor for a while. i added something for sticking lifters, forgot what it was been so long. anyway after that when i changed the oil it never came back. could check your timing.

 

exhaust leak is more probable that what you think, a inline six is longer than a v8 or v10 which makes it more prone to warping. Another thing it could be is your timing gear, these are known to be noisy and make a sound like you are describing. i didnt hear much in the video but could be my headphones or computer, it could also be any of the above mentions as well.

 

I can start with that since it is pretty simple and not a bad idea.
I never thoughat of that but that sounds probabal, what would you recommend doing, using a fuel additive if there are possibly carbon deposits, using a higher octane fuel, maybe knock sensor?