engine knock at start up 2000gmc

I have a 2000 gmc sierra 5.3 and when you first start it up when the truck sits overnight, there is a low end knock that last about 30 secs. I ran fuel and engine additives and still didnt work. Love this truck but this is annoying. Any suggestions or solutions. Has done this for over a year now.
Thx
bud

This is common in that engine.

Info - Engine Knock on Cold Start #01-06-01-028 Engine Knock on Cold Start

1999-2002 Chevrolet and GMC C/K Pickup and Utility Models 2002 Cadillac Escalade (2WD) with 4.8L, 5.3L or 6.0L Engine (VINs V,T,U - RPOs LR4, LM7, LQ4)

Some of the above vehicles may exhibit an engine knock noise that begins in the first 19,000-24,000 km (12,000-15,000 mi) of use The knock noise is most often noticed during initial start-up and typically disappears within the first 5-30 seconds (may last longer in extreme cold temperatures). The noise is usually more noticeable on the initial start-up when the temperature is below 10 degrees C (50 degrees F) and may be more pronounced on the first cold start following a long trip.

This noise may be caused by an interaction between carbon that has formed on the piston, the piston motion and the cylinder wall. GM Powertrain Engineering, and an analysis of engines with this condition, has confirmed that the noise is not detrimental to the performance, reliability or durability of the engine. THIS NOISE DOES NOT HAVE ANY EFFECT ON THE LONGEVITY OF ANY OF THE ENGINE COMPONENTS. Important At this time, attempts to repair this condition by replacing the engine assembly or pistons is not recommended.

Please share the information found in this bulletin with customers who inquire about this condition. In the event they have additional questions or concerns, please advise your Area Service Manager.
Type cold start knock in Google and see what you all find, its common on many makes.

USE GOOD FUEL, CHEAP FUEL CAUSES THESE PROBLEMS

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In addition, all gasoline outlets carrying the brand of the approved retailer must meet the TOP TIER standards.
Additional gasoline retailers are added to the TOP TIER list as they meet the standards. The retailers known to be on the TOP TIER list are shown below.
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Sunoco-Canada

well EVERY gen III motor knocks on start-up but if it does it that long i don't know. quick question did your truck used to be a u-haul truck? mine still had the logbook in it.

I have a late production '98 Sierra I bought used in 2001 with 42K on it. It has the 5.0L and exhibited the same condition you talk about...it still does 40K miles later. Dealer indicated it was carbon build-up and it would cost $300 for a top end decarbonizing...and no, my extended warranty would not cover this. Part of the "problem" with the knock (it's actually piston slap) has to do with the metallurgy of the pistons....they shrink when cold and have a tendency to slap a bit.

For the decarbonizing, try using SeaFoam injector/intake cleaner on a regular basis (like every 3k/oil change). I found out about this stuff and gave it a try...after 2 or 3 "treatments", it seems to be working as my start-up knock seems to be fading and not lasting as long as it used to...even in winter. Here's the website with the treatment steps:

http://www.seafoamsales.com/motorTuneUpTechGas.htm

Make sure you are outside when you do this! After you let the truck sit and restart it, a *lot* of smoke will come out the tailpipe. At that point take it for a drive until al the smoke clears...it will take about 10-15 of driving. I have used an entire can on my truck, doing it just before changing the oil.

Some people swear by this stuff and others swear it's witches brew. I just know in my situation it seems to have helped a bit...enough for me to continue using it.

Good luck...
Mike
98Sierra

I hear the top end cleaner at the dealer can help for about 15K
on your 5.3 but not much else you can do.
"sectors" 5.0, like mine, more likely suffers from
bulletin 99-06-01-003

See notation below.

Forum rules do not allow direct advertising or reference to a commercial site, sorry.

What is this in post #4?


http://www.seafoamsales.com/motorTuneUpTechGas.htm

This is a product we all use. We are concluding this issue as of now.

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