my truck is a 1994 f150 5.0 5spd 4x4. i've got this intermittent knocking sound. happens usually on start up for a quick second when the truck revs up, when i go above 2500rpm light or hard acceleration, and when the rpm's go down when i shift. i disconnected the spout connector and drove down the road and it didn't knock unless i lugged it. the vacuum reservoir has some rust holes but i got a temporary fix on it. does this sound like a spark knock or something else?

 

Pull the spout and verify that the timing is at 10 degrees BTDC. Does it go away if you use premium gas?

 

does not go away with 93 octane. also with the spout unhooked i can still hear a faint knock if i listen really closely but nothing like when its hooked up