Engine Noise at 2700 RPM?

[Stage 1]

At 2700 RPM under load the engine noise about double for about 100 RPM range. Above and below this RPM the noise is the same. Does not sound like a new noise, engine just gets louder. What is this noise and does it need to be fixed? This is a new truck that I just drove 2600 mile as part of break-in, first 700 mile not towing, then towed about 12 to 13K lbs. through mountains to the current 2600 miles.

Highest load towing was 2nd gear at 3000 RPM (w/lowest inst. fuel reading of 3 MPG). Averaged fuel consumption was from 9.2 to 11.1 MPG towing. Non towing in the mountain MPG was 15.7.

I can definately feel that the engine is a lot more powerful after the mountain/towing break-in.

I am very impressed w/ this truck! :D :D
Thanks for your help,

[WKener]

I am not sure about this, but could that be when the engine 'turns off' the pilot injection?

I have read about the DMax changing sounds as this occurs... Maybe this could be what you are hearing?

[Stage 1]

Wkener,
Thanks, I went back and did a search on pilot injection. Look like that is what I am hearing. Please let me know if it could be something else.

[bluenote]

I'd bet dimes to dollars that it is the pilot injection shutting off. Another significant sound you may hear when towing is the fan kicking on. When that big monster engages, it might sound like you have a jet engine under your hood for a couple of minutes.

[hdmax(mike)]

I have never heard the fan kick on, but the load noise stays as long as I hold the speed at about 90-92 mph. If I speed up or slow down it quiets down. So if it is the pilot injection, Why does it continue to make the noise for so long.

It also does it many times when I am picking up speed at a rapid rate, But then it is for a short time. (maybe 1-3 seconds)

[Stage 1]

Bluenote,
This noise is not the fan noise. As this was the first pull and I did hear that and figured out what it was. Yes the fan is loud. This engine noise is only at 2700 RPMs under heavy load ( e.g. pulling 12K LBS up a mountain). It did not seem to go away, obviously I changed RPMs to make it go away, so was not at that RPM for very long. Also, e.g. if pulling in 3rd gear at 2900 RPMs and grade pulled the engine down to 2700 RPMs it would make this noise. My uneducated thoughts were that it was from the injection system?? Again sounded like you just turn up the volume on the diesel noise about 2X.
Also this is my first diesel, so am learning about this technology.

[hoot]

I pretty sure you're hearing the diesel clatter at high rpms when the pilot injection turns off. It comes on somewhat abruptly and sounds like it's pinging terribly.

Normal

[MudNurI]

turn up the radio then you won't hear anything...

no seriously- I have never noticed a difference in noise depending on what rpm or mph I'm traveling at. Does this normally only occur with a load? I have to tow my K5 to the garage next week, wonder if I'll hear it then.??

Brandy

[Stage 1]

Brandy,

The noise has only occured while towing under heavy load conditions such as going up a mountain slope in 3rd or 2nd gear. I will have to accelerate through 2700 RPM wo/trailer to see if it makes noise.

[D/A]

I have the same noise you are explaining and at the same Rpm as you. I thought it was the pilot injection shutting off also. I am not totally sure of this but maybe someone knows for sure. Also I have this occur running solo also.

[DMAX-Hunter]

I too hear the same noise around 2800 RPMs. I am confident I am just hearing the pilot injection. This is a chatter type noise that occurs just prior to a shift at high-er RPMs.

[Idle_Chatter]

Sounds like it has to be pilot injection. I get a brief burst of it myself in a full-throttle run at the 2nd to 3rd shift, even unloaded. The Dmax is so quiet because of pilot injection. There's a short "pre-injection" before the main shot to start combustion and reduce the wave-front that causes Fords and Dodges to sound like they're crushing rocks. At high rpms (above 2700) the piston is approaching top dead center so fast that there's no time for the pilot shot and injection is all in one shot (like our poor, noisy, ugly and less refined stepsisters) and voila! you're hearing what the Dmax would sound like without pilot injection! I don't see it as any problem, the DMax doesn't do it for long and other diesels run that way *all the time*! :D

[bluenote]

Here's a way you can check for sure while running empty. Put your gear selector on 3 and take off. You'll hit that 2700 rpm range at normal road speeds, and most likely it'll sound the same as you are reporting under load. I've done this to show my wife the difference in the sound with pilot injection on and off.

[Stage 1]

FYI, I just tried an acceration run this morning to 3000 RPMS wo/load and no 2x noise. Will try again locking in 2nd gear and see if it makes the noise. Question on pilot injection, does it change based on how much fuel is being provided to engine?

Also, the Auto Show will be here later in December, and the GM exibit always has various product design staff attending to answer questions. Will ask about this noise, along with explaination of how the pilot injection works. If I talk long enough w/them usually get their work e-mail for future questions.

My wife went for here first ride today and said the truck is not bad! This is a big improvment over where our truck discussion started.