i posted this on TRS but thought i could find some help here
so i picked up a sweet 89 ranger for a DD, it's a 2.3, 5spd, standard cab and box. it has 159k on it and the motor was replaced at 100k. anyways, if you rev the motor, or drive through the gears there is a rattling noise similar to what a heat shield would sound like.
i checked the main muffler and pulled that heat shielf off, then checked the one on the exhaust manifold and pulled it off. the noise is still the same and i've tracked it to under the valve cover
it is evident above 2500 rpms or so (no tach) and is a little louder as it comes down. if you shift early you won't hear it, and nothing at idle. but if you go through the rpms a little bit it will rattle and you can definately hear it as the rpms come down. i'll get a video of it when i get home. it really sounds like a heatshield rattling, but i 've removed them and checked the one on the cat, which is good.
i'm assuming it's something to do with the valve train. i've searched and didn't find a good answer to explain some similar problems. i just changed the plugs and wires (made the noise before) just to get it running better. this is my last problem to fix before it'll be top. hopefully i don't have to pull the valve cover cause it looks like the intake has to come off too. i think i'll try some seafoam as well, but doubt that will fix it. it's definately not detonation either.
sorry for the long post, just wanted to explain everything. and i'll post the video up tonight
also, the noise goes away once you go above approximately 4500 rpms, which i only did a couple times. so it's only doing it between 2500 and 4500. seems like the valve adjusters or whatever these little motors have can't keep up with the acccel and decel of the motor and the rockers are tapping or something