hi there my name is Wes I'm new here to diesel power forums. what i have is an 02 6.6 duramax with a 6 speed manual trans and out of the blue I started hearing a nocking noise from under the hood. It sounds like a poker card in a bicycle wheel. I took it to my regular diesel tech. and he thinks it might be my vacuum pump. but a friend of mine thinks otherwise. Does anybody out there have any ideas on what it could be or how I can check the vacuum pump before I take my motor apart.     Thanks Wes  

Hey bud, I have never seen any vacuum pumps on any of the duramax equipped light duty trucks. I think your tech is mistaken with his diagnosis. I have run across some noises from several motors sounding like an occasional lifter ticking. GM has posted a bulletin for such noise as "non detrimental to the function and longevity of the motor". They have no current fix that I know of. My only solution for my customers has been to try a 15W40 synthetic oil such as Amsoil(makes a difference b/c of better flowing ability and friction energy absorbtion, basically, keeps things quieter) and maintain the oil drain intervalls acurately as you should. Do not add any additives to the oil. No engine manufacturer will ever condone any oil additives. The noise should subside or atleast become less frequent or noticable after oil change if this is the nature of the trouble you are describing.  

Hey there,first off thanks for replying. i should have added that the sound started just before my last oil change and thats when i had him look @ it or should i say listen to it the sound is still there but that dosen't mean thats not it but just in case any other suggestions?      

The only other thing I can think of that I have seen before would be the power steering pump. On atleast 1 other truck, I've experienced the p/s pump making a noise internally. It didn't sound like you are describing, but it made sort of a whistling sound like a boost leak but under idle. I would check the fan shroud and the fan blades to make sure they aren't contacting anything. I cant think of any other "ticking" sounds like that.  

thanks agian, would it help if i told you what side the noise is comeing from i dont think i ever said, the noise is on the passenger side.  

A few more things I thought of that you could check would be the support bracket at the rear of the turbo downpipe (pass side) just behind the manifold. I have seen the brackets crack and make a ringing sound or a very fast ticking depending on rpm's. Only other things I can think of @ this time are a leaking exh. gasket on the manifold (could be gasket or broken bolt), a loose pyrometer probe (if you have one), or a bad/leaking injector (most likely notice a power loss though or rough idle).  

cool richie i will look in to all of the above and let you know what i find out .thanks agian for all your help.
wes  

just wanted to let everybody know that i am very thankful for your in put on my problem. after my wife emailed her uncel who works for the GM tech school in Washington and specialize's in diesel's.he came down to my house in oregon and found the noise.it was in fact a belt driven vacuum pump on the pass. sid on the bottem.    
thanks agian Wes  

Hey Wes, thanks for the update. Sorry for jumping to conclusions about your mechanics find. Guess he was right. I honestly never saw a vacuum pump on these trucks. See that, you learn something new everyday! Glad you found it though.