my 84 300I6 has a small knocking sound from the front of the engine. i thought at first either the ac compressor or steering pump was making it, but they are not the problem. i wouldn't think it would be the crank bearings because the engine has only 93000 miles and has had a decently easy life. the knocking increases with rpm but not directly, it lags behind when reving the engine. does anybody have a clue as to what this might be

Eric

 

"Sounds" are hard to diagnose, when you aren't there in person... Is it a knocking, or a tapping? A tapping, or a quiet wshk-whsk noise? Since you've been able to look under the hood with the engine running, I'm guessing it happens when not under load, which, afaik eliminates something with the efi, but I'm only a novice at that; The owners manual for my '91 notes that a quiet wshk-wshk (they don't actually call it a wshk-wshk, mind you)when accelerating is the efi adjusting, although it freaked me out the first time I heard it. Anyhoo. You could have a lifter tapping, if the sound is rythmic enough, or something as simple as a pulley going bad (those idler/tensioners are notorious - caught mine just before it went. phew). I don't have to tell you to not put your face too closely to anything moving, right?

If you aren't sure what it is, you should have someone you trust take a listen - it could be nothing, and it could be serious.