I have a 99 6.0L engine that has made two odd noises since day one when I bought it new. The dealership says they can't hear a thing or that the noises are normal.

1. The engine makes a knocking noise during cold/cool (est. 30-60 degrees ) weather starts, and idles that way until it gets up to temp. One individual thought it was the free floating rest pins in the pistions.

2. In warm weather not cold, the engine clatters under slight acceleration and when I lug the engine slightly during every day driving.

The truck is bone stock with an auto trans.

DOES ANYBODY HAVE ANY SUGGESTIONS? <img border="0" alt="[bang head]" title="" src="graemlins/gr_banghead.gif" />

 

I read somewhere 7 out of 10 new 4.8,5.3,6.0 experience the same knock. Gm trucks usually develope the problem between 15k and 30k. Gm knows about the prob and says its "nothing to worrie about" take it or leave it. I dont know about the second prob but are you sure its the engine? Kinda sounds like a tranz to me, but what do I know! ha <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

 

Let us know where you read this.Or was it someone on a truck forum spouting off numbers?

 

Answer to your first question is it sounds like you have the standard cold start knock that a lot of people complain about with the older ls1 truck motors. Some people were able to temporarily get rid of the noise by using GM's top engine cleaner. Answer to your second question is it sounds like the same problem I had with my truck. The noise that I had sounded like spark knock but it would do it with any grade gasoline & you could only hear it from the drivers seat with the window up & the radio off. My noise ended up being exhaust noise that was being transmitted through the plastic steering boot for the cab. To fix the problem I just cut some packing foam (similar to acoustic foam) into an elliptical donut & packed it into the boot on the inside of the cab (noise gone).

 

If it makes you feel better, almost every one I have seen has the cold knock. I found my 99 6.0 knock varies slightly with the oil I use. The quietest it has been is with the current oil. Mobil Delvac 1 5-40. It is synthetic H-D Diesel oil. I’m going to doing start oil analysis on it now and see what happens. I have about 48K on my truck.

I have also heard the “clatter noise” you are hearing. Running a scan tool did not show any knock retard, but I haven’t looked further into it yet. I might try 2ksleepers solution.

Now that I have quieted down some of the other noises, I’m finding new ones!

 

That clatter noise you talk about might be the piston slap that many complain about. Just a thought. It is a common problem.

 

I think you have carbon-buildup on your valves and pistons. Here is one guys approach--read all the way to the bottom:

http://www.nissanperformancemag.com/...cleaning.shtml

Here's another idea:

http://www.ultratune.com.au/ult2000.htm

Dan

<small>[ April 16, 2003, 04:28 PM: Message edited by: LIGHTNINROD ]</small>

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 2ksleeper:
<strong> Answer to your first question is it sounds like you have the standard cold start knock that a lot of people complain about with the older ls1 truck motors. Some people were able to temporarily get rid of the noise by using GM's top engine cleaner. Answer to your second question is it sounds like the same problem I had with my truck. The noise that I had sounded like spark knock but it would do it with any grade gasoline & you could only hear it from the drivers seat with the window up & the radio off. My noise ended up being exhaust noise that was being transmitted through the plastic steering boot for the cab. To fix the problem I just cut some packing foam (similar to acoustic foam) into an elliptical donut & packed it into the boot on the inside of the cab (noise gone). </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">same as I did. Thanks to Bob Prim on Pacific Audio. It is valvetrain noise that you somehow hear. The cold start piston slap is very common too. Don't worry, I have spun my 5.3 to 6200 and it hasn't flown apart. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

 

Hehe, my '01 5.3 has piston slap too. GM sucks and needs to fix it. I read that the pistons were just a bit too small for the bores...

Weird thing is that my old '99 5.3 didn't have that problem. Of all the other broken stuff, the motor was great.

 

Thanks for the replies guys. I'm looking into the second noise. I will probable do the fuel system flush for now, whether that's it or not. The truck needs it since I'm at the 60,000 mile range. Although just to refresh it's been doing it since day one. Can anybody recommend a good kit to clean the fuel system? Also, what's a good preventative fuel additive for in between oil changes, any brand recommendations?
Would rerouting the water flow to bypass the throttle body help? Could this be part of the problem. I do live in Texas were the summers get a little hot.