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The other morning when I was getting on the freeway I put my foot into it a little bit and noticed a pretty good knock coming from the engine. I backed out of it and it went away. The truck had been running for 20 or 30 minutes, so I don't think it was cold. I checked the oil level and it's fine. So any ideas what it could be? I've only got 20K on the truck and its bone stock.
 

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The other morning when I was getting on the freeway I put my foot into it a little bit and noticed a pretty good knock coming from the engine. I backed out of it and it went away. The truck had been running for 20 or 30 minutes, so I don't think it was cold. I checked the oil level and it's fine. So any ideas what it could be? I've only got 20K on the truck and its bone stock.
Fill out your sig so we can see what you have. What year is it?
 

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Sorry about that. It's a 2004 GMC 2500HD with the LB7. Bone stock with about 20K miles on it.
 

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It's more of an engine noise. The first thing that came to mind when I heard it was valves. It sounded kinda like my old 6.2 when it would first start up on a really cold morning.
 

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Perhaps the pilot injection kicked out,usually about 2600 rpm this can happen.Will really get your attention.
 

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Discussion Starter #8
Fuel filter was replaced about 3k miles ago
 

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mine ended up being serious, but you have probably, partially plugged injector which causes a fuel knock under load.
 

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Mine does this so I took it to the dealer and they said that the injector balance rates were good so they would not do anything. I'm about ready to go to another dealer because the truck should not hammer like it is.

Is fuel Knock really bad for the motor? And is there any way to clean the injectors so I don't have this knock? It's really anoying:mad: .
 

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This is probably a long shot but worth trying nevertheless. I had a similar knock under load that baffled me for months. Sounded just like injectors. You would never guess what it was. Below is the page of the thread where the source was found/fixed (Post #116). You can skip to the beginning and read my symptoms. I think at least 3-5 other guys found this to the be source of their knock as well.

http://dieselplace.com/forum/showthread.php?t=54560&page=12&highlight=knock+load
 

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Discussion Starter #12
Thanks for all the tips everybody. It didn't sound like it was coming through the dash, so I don't think it was the "coolant problem". I'll see what the dealer says. If nothing else I'll change the fuel filter again and run a bottle of injector cleaner through it.
 
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