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Duramax 6600 Discussion Forum for the Duramax 6600 Diesel Engine, including the LB7, LLY, LBZ & LMM engine specific topics.

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  #1  
Old 09-01-2012, 07:08 PM
mudchief mudchief is offline
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Join Date: Jun 2006
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Default Need Help - Loud Knocking Noise

Alright I need help. I have got an 05 duramax with 165k miles. Had GM replace all injectors 14 months ago. However the motor has developed a loud knocking noise. When the noise first became present, I stopped at a truck stop and poured in some Lucas injector cleaner. The noise then went away, but after a few days, the noise is back. The noise is very loud at all continuous at all rpm's. The truck has full power and does not smoke, but sounds like a "rod" is out.

I am 1600 miles from home and I took the truck to nearest GM dealer. They apparently investigated and called me back saying it appears that the "rist pin" on cylinder #4 is bad and it will be $11k to fix.

Dealer says injectors tested all ok.

Here is what I struggle with: They say that they believe it is the "rist pin" because when they disconnected the injector on cylinder #4, the knock goes away.

I would think that if it is a "rist pin", that the knock would still be present but maybe not as loud due to no combustion.

Please give me your thoughts before I find myself in a position of getting screwed for $11k and a new long block, when it may be something else.
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  #2  
Old 09-01-2012, 07:49 PM
Kennedy Kennedy is offline
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I would swap #4 injector to a different hole and do the cylinder cut ouit again to see if it stays with #4 or follows the injector.
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  #3  
Old 09-04-2012, 02:35 PM
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More Power More Power is offline
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Quote:
Originally Posted by Kennedy View Post
I would swap #4 injector to a different hole and do the cylinder cut ouit again to see if it stays with #4 or follows the injector.
Excellent advice!

By the way, #4 is second from the front on the driver's side of the engine.

Years ago I was visiting a local diesel garage, and walked by a mechanic working on a GM diesel pickup with the hood up (a 6.5L diesel). He was revving the engine and listening to what I was sure was a rod knock. It sounded pretty bad. I mentioned that to the mechanic, and he said "watch this" as he loosened an injector fuel line fitting on one injector. The engine began missing on one cylinder and the knock completely disappeared after a couple of seconds. Then he tightened the fuel line fitting, and the knock returned in a couple of seconds. A bad injector was the cause.

Can't loosen a fuel line fitting on a Duramax injector, but swapping the suspect injector with another is the next best thing. Jim
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Old 09-05-2012, 06:01 AM
GM Customer Service GM Customer Service is offline
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Quote:
Originally Posted by mudchief View Post
Alright I need help. I have got an 05 duramax with 165k miles. Had GM replace all injectors 14 months ago. However the motor has developed a loud knocking noise. When the noise first became present, I stopped at a truck stop and poured in some Lucas injector cleaner. The noise then went away, but after a few days, the noise is back. The noise is very loud at all continuous at all rpm's. The truck has full power and does not smoke, but sounds like a "rod" is out.

I am 1600 miles from home and I took the truck to nearest GM dealer. They apparently investigated and called me back saying it appears that the "rist pin" on cylinder #4 is bad and it will be $11k to fix.

Dealer says injectors tested all ok.

Here is what I struggle with: They say that they believe it is the "rist pin" because when they disconnected the injector on cylinder #4, the knock goes away.

I would think that if it is a "rist pin", that the knock would still be present but maybe not as loud due to no combustion.

Please give me your thoughts before I find myself in a position of getting screwed for $11k and a new long block, when it may be something else.

Mudchief;293407,

Please keep us posted on the status of your vehicle. If you have any questions, comments or concerns please feel free to contact me.

Thank you,

Tina
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