Ok at about 85-90 mph on the freeway at about 2800-3000 rpms the motor makes this weird clatter, it will do it and then stop and then do it again and it feels as if the truck stops to pull (as in acceleration) when it does this. Sounds almost like a clattering motor (gasser) but not sure what to think. Temp and oil press are normal, nothing else seems to be wrong. I know that is close to the redline but still have 500 or so RPM's to go, could this be the reason? Just curious. Edited by: GMC2500HD

I was told that the noise was the "pilot injection" transitioning on and off at about 85 mph. I noticed the same on/off noise with cruise set to 85 on level ground. There are several threads where others have experienced the same noise. If it is the pilot injection in your case, its normal according to GM. http://www.dieselplace.com/forum/smileys/Approve.gif


It definitely scared me when I first heard it and didn't know what it was. http://www.dieselplace.com/forum/smileys/Confused.gif

Pilot injection can not funtion at that speed, d/max turns into regular old diesel at that speed.

If I Remember Right It's Your RPM 2800

A friend of mind also has a 03 Duramax. When on I-95 going about 80-85 mph. He was having a clattering noise. He took his truck into a GM Dealer and they checked it out. They said they believe the noise was coming from AIR that was in his fuel. He told me they check everything on the truck. I haven't seen him in the last week but he said he was going to get some kind of fuel filter that will remove the AIR in the fuel.
Good Luck in finding, what is causing your problem.

It's the Pilot Injection. The only air involved is in the Non Diesel Knowledge head of the Service Advisor your buddy spoke with.Just not enough time for the pilot injection, which reduces noise, when the motor gets above about 2750 rpm. It cuts out, and you are driving a plain old, noisy diesel, till your rpm's drop back down.


Watch your tach when you are running up the speed to the 85 mph range, the noise will come on at the exact same time, every time.


Just the nature of the Duramax Beast!http://www.dieselplace.com/forum/smileys/Smile.gif

Thanks Silverdogs
I just called my buddy an told him about this. He is going to check his rpm's the next time he is on I-95 when he can get up to 80-90 mph's. Then he will drop off the speed an rpm's to see if this is his problem . I told him I think it is. If so; he said he is going back to the dealer and tell them about it. I might even try it on my truck to see if it happen's.
Thanks Again

Well as long as I am not hurting anything then I will not bother with it. I did it again today several times and it did not seem to do anything. Just noisy thats all. No big deal. Edited by: GMC2500HD

The pilot injection on my 02 kicks out at 2600 RPM. Later! Frank

Frank,


it's just scared of you.http://www.dieselplace.com/forum/smileys/Big Smile.gif


I've only heard mine once during a test pull with my trailer. Scared my wife half to death. http://www.dieselplace.com/forum/smileys/Wink.gif


When I nail it unloaded I just can't hear it. I never tried to hold it at RPM to find out. I know what it sounds like and don't worry about it anymore..


Pilot Injection is kind of like putting a muzzle on the beast. The Dmax likes to roar once in a while. http://www.dieselplace.com/forum/smileys/Approve.gifEdited by: DavesDmax

And roar it does, on every on ramp! Love that push that starts to come on, so nice and strong!

My 2000 Dodge Cummins (soon to be ex) sounds like that all the time, I've only suffered minor hearing loss.


My new LLY d/max is scheduled to arrive in two weeks. I can hardly wait. It will be nice to be able to listen to the radio again.

yes its the pilot to main injection transition

You should hear it at 4,000rpms during grade breaking and you hit the go baby pedal!! It really talks for a second or two until it upshifts!! That caught my wife's attention... http://www.dieselplace.com/forum/smileys/Big Smile.gif


Bob

I think that you hit the "4" key instead of the "3" key. D-max redline is only 3500. If you are getting your D-max up there in the RPM range it is not going to last very long and then that will get YOUR attention. Edited by: GMC2500HD

Nope, 4x4man is correct.


I read that in the GM Diesel supplement that during grade braking mode the Duramax can rev as high as 4800 RPM's with no ill effects.


Above that I believe, it up shifts and says "It's your problem, use your brakes you tightwad!" http://www.dieselplace.com/forum/smileys/Big Smile.gif

Interesting, did not know that you could run one that high. Wonder what it can take in the normal RPM's just running? I was curious what some of these guys who race them (1/4 mile) are getting into RPM wise?

Without a box that increases your rev limit, you can only go up to 3200 rpms. With grade braking, you can get somewhere around 4800 rpms (I havn't seen that yet). If you look on your tack, you will see a dotted red line that starts at 3200 rpms, then a solid red line at around 4800 rpm or so.


I believe the quad box allows you to move the rev limit up to 4000rpms.