My 90 ranger xlt 4x4 5spd 2.9 sat for some time, apart. I bought it as a jigsaw. 5 weeks later runs good, excelerates, good power. But every other time I run it knocks like its coming apart. Other than the sound it seems to be running good. No overheat. Good oil pressure.im gonna pull valve cover later, could it be plugged oil passage from sitting? Fix w compressed air?? Could I get so lucky? Just wondering if I'm On the right path.cuz it still runs super. Knocking or not. Please advise. And thanx,

 

Tapping or knocking?

Tapping is valve train and the 2.9l had an issue with that as it got older, cam bearings would wear and reduce oil pressure at the top end.
Run a thicker oil.

Knock would be a connecting rod.
With engine warmed up and idling if you can hear the knock then pull off 1 spark plug wire at a time, yes engine will miss, if knock goes away then that cylinder has a bad connecting rod bearing.