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Discussion Starter #1
I finally had a chance to try a test pull on our 9000 # 5th wheel with the new truck today. When I first started out I noticed that the engine made a loud noise right at a shift point. It reminded me of a severe ping or spark knock on a gas job. After 10 mins it seemed to be fine. Being new to a diesel, I was wondering if this is common.

P.S. I was in tow haul mode, the engine was warm, I was going up hill, and I have around 900 miles on the truck.


2004 2500HD D/A
 

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Without being able to actually hear the sound first hand,
it's hard to honestly say. Where are you located?? Chances
are that a fellow member is close enough for you to hook
up with for a first hand opinion. Another thing to bear in
mind is that a new truck like yours reacts differently
to hauling a load than a well "seasoned" one.
Was the noise occuring at around 25-2600 rpm??? If so
than you might be hearing the pilot injection shutting
shutting down.......just a guess.
Good luck,
Tom
 

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I have the same thing. It doesn't just do it when pulling though. It is always when the truck is about to shift. I suspect it has to do with the de-fueling and turbo boost coming down so that the computer can command a shift. It seems to only happen the first couple of times and it seems to learn and shift faster the next time. It sounds like on a gas engine when you have a bit too much timing and it starts pinging or pre-detonating. This noise concerns me a little.


Anyone else have any opinions.
 

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Glad to read your post. My truck purchased in June is doing the same thing.I'm pulling a Sunnybrook 5th wheel loaded at around 12,000 pounds.I now have about 8,000 miles on the truck.I've had the dealership service tech ride with me while I was pulling our 5th wheel and the same thing happened. They have no idea's..............


It doesn't do it all the time; but right before it shifts into 4th the engine sounds like the rpm's go high. The rpm on the tach does not change. I tow in the tow haul mode and have had this happen acouple of times while driving at a steady speed. When this happens it only lasts for a second or two. Hope we get some answers.
 

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The link below imparts an good education on the noise you describe; posted by "modified" on 10-26-03.


Topic: sound changes at 2800 rpms



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<TD class=bold width="20%" background="" bgColor=#f8f7ef><A name=15153></A>modified</TD>
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<TD class=smText noWrap>Posted: October 26 2003 at 7:09pm </TD></TR></T></TABLE></TD></TR></T></TABLE>
Here’s a description of Pilot Injection, copied from Overdrive Lockout Info at :

http://dieselplace.com/forum/forum_posts.asp?TID=754&PN=1



Diesel engine fuel injection systems that use a common rail system, as the Duramax™ diesel does, may or may not have what is referred to as pilot fuel injection at the lower engine speeds. Pilot fuel injection is defined as a pre-injection of a small quantity of fuel 5 to 20 crankshaft degrees before the main fuel injection. This pre-injection softens the main injection pressure rise and reduces combustion noise. At engine speeds above 2600 RPM, and a fuel quantity supply greater than 35 cu mm, it is necessary to eliminate pilot injection to meet emission requirements. When driving at or above these speeds, main injection combustion noise may be noticeable. It is normal and not harmful to the engine.


When traveling in 5th gear, the pilot injection to main injection transition is typically in the 136 km/h (85 mph) range, however it may also be heard under heavy acceleration and when pulling loads up a hill during shifts at or above 2600 RPM. Customers that install the fifth gear inhibit switch may encounter the fuel knocking of main fuel injection at speeds around 107 km/h (67 mph) in fourth gear between 2600 and 2700 RPM. This sound is considered normal and is to be expected.


http://www.dieselplace.com/forum/forum_posts.asp?TID=1614&KW=pilot+fuel
 

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I have read that. It is even in the supplement manual. THis sound is more like when it goes to shift the engine changes its sound altogether and it sounds like pinging. It mostly does it in tow/haul mode and settles down after a couple of shifts. If the shift is delayed because it is learning a new shift because it is pulling a different load then I get this sound for the first few shifts. It is a fairly loud pinging. Loud enough even my girlfirend looked at me funny. It is not the injection changing at high rpm. That sounds a fair bit different. I think it is more related to how the motor and tranny work to shift. The motor de-fuels and it makes this noise. Once it shifts, the sounds goes away. I just bought my truck the first of September and I have about 6000 miles on it.
 

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Discussion Starter #7
Thanks. This sounds like it was what I experienced.
 
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