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Registered
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519 Posts
Discussion Starter #1
My 02 GMC 4.8 has a knock on cold starts, but it stops the knocking sound after it warms up. Still runs fine. What could be causing this and should I be worried? I was thinking about getting an EFI Live tune but don't want to screw anything up any more than it is.

Thanks for any help.
 

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Resident Guinea Wop
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14,542 Posts
Piston Slap.

www.pistonslap.com


Don't let that site bother you though. It was written years ago in the hopes of a HUGE classaction lawsuit.

Never happened. Why?

It's been around forever, and not a SINGLE member on here has had a problem. 75% of these motors now have 75K+ miles on them now. Many with 150K+ and ZERO problems.

Mine does it as well.

Just noise. Nothing to worry about.
 

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Speed Holes
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5,190 Posts
Piston Slap.

www.pistonslap.com


Don't let that site bother you though. It was written years ago in the hopes of a HUGE classaction lawsuit.

Never happened. Why?

It's been around forever, and not a SINGLE member on here has had a problem. 75% of these motors now have 75K+ miles on them now. Many with 150K+ and ZERO problems.

Mine does it as well.

Just noise. Nothing to worry about.

nice explanation.

Mine has the signature piston slap, but mostly only noticeable on those cooold cold winter mornings. Over 150k on my '02's odo too.
I just make sure to let her have some time to warm up a little bit on cold starts, or I just take it super easy if I'm in a hurry; no twistin' the ignition, poppin' it into drive, and immediately mashin' the pedal!

Unless you're hearing a different "knock" you shouldn't have problems.



...can't see the photos above, only red x's... ???
 

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Registered
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519 Posts
Discussion Starter #5
Can't see the pics either.

Thanks for the info. I bought the truck last summer and of course it didn't do it when it got 100+ outside. Nice too know its not too serious. Only has 117K on it
 

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AllOffTopic.com FTW!
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8,460 Posts
http://www.pistonslap.com/PistonSlap.wav

So, piston slap sounds like a clattering/clacking sound, like impacts, as on might expect from its description?

Lately I've been noticing my truck sounds kinda diesel-ish for a few seconds after I start it, and have been attributing it to oil starvation because my driveway is a hill. It's a smooth diesel sound, though, not like the piston slap wav file.
 
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