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?

 

Sounds like knock to me. It can happen at lower RPMs, like when you downshift. Maybe try running some higher octane gas next time you're empty and see if that helps?

 

what is spark knock? I've never heard of it before.

 

It's the same as regular engine knock you hear about. Also called detonation or pinging.

 

Ah gotcha. Something no one wants to hear. Thanks for the info.

 

just ran a tank of 93 octane. no change