I have a 94 F -150 2x4 with a 4.9L inline six with 78,000 miles on it.
When accelerating hard or lightly and going up hills it has a ticking sound like a diesel that's not real loud but drives you nuts after awhile. I was told by just friends it may be a sticky valve or a small exhaust leak.
Can't see it being those because the motor sound quite and smooth at idle and and even while revving in park. Cant find a exhaust leak because it dose not make the noise when idling.
The ticking seem to come more from the lower passenger's side when driving. I even tried High octane gas to see if its a fuel grade pinging issue but it did not seem to quite it down.
probably is an exhaust leak that only occurs when the engine is under load. The exhaust route goes right under the passenger side of the vehicle so that make it even ore possible that, that is the problem
I had the same problem on my 95. It was the air injection tube #6. If you have access to a wire feed welder it is a cheap fix assuming the tube is not rusted out. Pain to take everything apart just to get to it. I took the whole rail off to fix it.