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Discussion Starter · #1 ·
I have 99' Z71 5.3l with about 120k on it. when I start it up when it's cold outside it sounds like it's spark knocking (the diesel sound) anyone else have this problem? And advice on a fix?
 

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I've heard that it's due to the design of the pistons, since they are skirt-less.

Does it go away after the engine warms up?
 

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Discussion Starter · #3 ·
yeah once it warms up it goes away. but I have been doing alotta research on the net for the last couple of days and I guess its called cold start knocking (csk) and they say its from carbon build up and that you can cure this problem by putting sea foam into your fuel system. that is what i have read anyway
 

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It's entirely likely. A can of seafoam will help the engine in other ways as well, so even if it doesn't fix the knock it wouldn't be a waste of money to try it.
 

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Sea Foam Motor Treatment available at NAPA, O'Reily's, and Pep Boys.
 

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Discussion Starter · #8 ·
awesome thanks for all the info guys!!!!:great: So from what I have been reading on this stuff you just unhook your brake vacuum line and poor it in right?
 

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awesome thanks for all the info guys!!!!:great: So from what I have been reading on this stuff you just unhook your brake vacuum line and poor it in right?
The vacuum line will suck it in. Only use about a third of the can in the vacuum line and be prepared for a lot of smoke. I put some in a separate container cause if your not careful you'll suck the whole can up. Also be prepared to pinch off the vacuum line and rev the engine if it starts to die out.
 

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Discussion Starter · #10 ·
you say rev the engine cause other places I have read say to let it die? :shocked:
 

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Seafoam

big, big fan of seafoam. fantastic stuff. i seafoam all of my cars on a regular basis twice a year.
not well known feature of seafoam is that you can not only put it into fuel tank but, also, pour it into crankcase - and drive with it in oil! i had over 2000 miles like this on my ranger, no problems. i contacted manufacturer and they told me that it is petroleum based (if i remember correctly), anyways - it's based pretty much on the same compounds that engine oil is, and that's why it does not harm engines. so, i just run few hundred miles on it before oil change.
if your truck does not take oil - switch to amsoil or royal purple. you'll see a lot of difference. and, for truck's sake, flush with flush oil when you do oil change.
as of knock - they say silverado is infamous for cold knock. i have seen many posts on that, and believe it is lifters. engine does not have OHC plus is made the way it's made. many call it clunker - noises from slip yoke, intermediate steering shaft, transmission, transfer case are a general complaint. someone sent me a lengthy letter from chevy, full of official bs why there are so many noises and why chevy will do nothing to fix it. they say it's "normal". not normal on tundra or titan, but what do i know. did i mention clunck from driveshafts at low speed turns in "auto 4 wheel drive mode" ?
 
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