My 2003 F250 with the5.4l and over 100k miles rattles like low oil pressure to lifters or may be lean burn knocking. It is a light clicking when first started and gets louder when I put it in gear (automatic). After a few seconds of running under load it is quiet. No heavy knocking when under load.

Adding octane booster and injector cleaner has not had any noticable affect.

Ideas on how to pin point the source?

 

a guy at a dealership told me that the noise was from exhaust manifold bolts that are broken , but still in the manifold , that is why once the manifold warms up it goes away . mine has been making this noise for about two years i keep meaning to fix it , but i have just dealt with it .

 

I dont blame you its not an easy fix all that drilling and tapping it sucks just trying to get to it. Hey Jeff you might want to try some seafoam that **** works wonders!!

 

Mine was doing the same, it was the exhaust manifold. They are relatively easy to get to. Pull your front wheels, then pull your fender wells. All really easy to get to once you do that. After I replaced my manifold gaskets, the rattle went away. And yeah, I had to tap two bolts on one side and three on the other. Before you put a wrench on them, hose them down with some good penetrating oil. Good luck.