Silverado Knock sensors.
 

My 01' 5.3l is throwing the DTC P0327 for the knock sensor #1. Previously it shot me the #2 code as well. I have read up and heard that they are located under the intake manifold(thanks GM) and can go bad due to corrosion from water and grime. There are two things keeping me from just replacing them. First, in the morning when I go to warm her up I can sometimes hear a very noticable knocking until it gets warm. Second, My truck likes to make little "pup pup pup" noises at deceleration making me thing its running rich for some reason. I run and have been running 91 octane for the past year. Do you think it could be a timing issue, or just the sensors going bad? To be completely truthful I have run her through some seriously gnarly creeks and puddles at considerable speeds in the past years. I'm leaning towards the theory that they have gone bad from my previously ignorant actions...lol.
Any thoughts will help guys... Thanks!
Shane.

All too common problem...if you're getting the code, I would definitely replace the sensors and harness. When/if you do, silicone around the rubber grommets prior to install.

Been there done that. Yes, they are under the intake so go ahead and get the intake gaskets as well. There are 2 knock sensors under there so I would replace both at the same time. Also you will need the harness (unfortunately it's a dealer item) I remember it wasn't that expensive though. The harness has 2 rubber plugs that are supposed to keep water out (obviously they don't do a great job) when you put the new ones in get some black RTV silicon and dab some around the rubber boot (bridging the boot to the lower intake). GM recommends leaving about 1/4 inch or so on the back side of the plug without silicon. I can't figure out why, but I have listened to them when I have done it. My personal truck needed them and I couldn't really tell a difference as far as the way the truck ran before and after. There are also 2 foam pieces under the intake that is suppsoed to aid in engine warm up...TOSS them in the garbage! Your truck will warm up exactly the same and now you will have an "Air Gap" intake like edelbrock sells. I think they actually trap the water and grime in there and contribute to the knock sensor failure anyway. The knocking in the morning is totally unrelated and is actually piston slap that GM says won't hurt anything. They pretty much all do it when they get more than about 60K miles on them. Just let the truck warm up before doing any smokey burn-outs! The "pup, pup, pup" could be a few different things. I would do the sensors and see if it still does it. Good Luck!

Thank you so much, thats the response I've been waiting for. Now I've heard that you need to get the GM sensors or it might not work, is that true? Thanks again!

Intake gaskets are reusable.

Come on Yankee don't be cheap. I personally would never reuse an intake gasket, maybe something a little easier to get to like a throttle body gasket, but not an intake.
You do not have to buy the factory sensors, just get the harness from the dealer. Let us know how it works out.

Cheap? It would be a pointless expense - not "cheap". The gaskets are made to be reusable. I've had my intake off I don't know how many times, I'm pushing 600rwhp and have no issues and neither do any of the other guys making any real power. So if we don't - why would he?

Wow I think I hit a nerve...we all have our ways of doing things. I am not saying you can't reuse them just it would be a shame to have to pull it back off b/c the gasket didn't seal properly, and being a used truck who knows how many times it has been taken off and put back on. I guess I shouldn't have said I would never reuse an intake gasket. If I had just replaced them and had to pull the intake I would not replace them again, but your talking about a 2001 truck that possibly has the original gaskets. They may get a little brittle after 8-9 years don't you think.
Wow 600 RWHP that is very very impressive!

No sir - no nerve damage. :) Just do what I can to help out and I've never seen one not seat properly and if the engine really hasn't been modified, I doubt it's been removed or removed enough to make a difference. But true, they may get brittle after a while. My truck is a '99 though and I never had issues prior to swapping the engine and I removed it a few times. My way definitely isn't the only way - just offering advice based on my my experience and those I race with. :)

Well now that I've got some helpfull people here, I do have another issue. I hope yall can help, because my other thread isnt getting any hits. At low speeds my tranny will stay in gear and shift from 1-2-1-2 like crazy as the speedo jumps up and down, ABS light comes on,and the e-brake light comes on. I have replaced the two VSS on my transfer case at 30$ a piece, had my ABS module refurbished for 160$, and had my wheel bearings and front ABS wheel speed sensors checked at 100$. They are all fine. Problem still exists. I cant find a soul on here to help let alone the one mechanic in town that I trust, but yall seem like some ASE certified mechanics or somethin...lol. I'm scratching my head here, the only thign I can think would be another VSS on the tranny somewhere. Anything would help guys.
Thanks again, your input is greatly appreciated!
Shane.