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Discussion Starter · #1 ·
So I noticed this the other day and was wondering if there is anything connected.

When a 6.7 idles for a few minutes, you start to hear the motor get a slightly deeper growl to it versus when it first started idling. Its not a progressive thing either. It is a sudden change. Anyway, I was in traffic and noticed my truck started getting the deeper idle after a few minutes. When I started to go again, it felt like it had more umph to it. Was just curious what is happening and if it would cause more power potentially. It could have been all in the head as I rarely sit in traffic to experience it often.

:confused013::thumbsup:
 

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Discussion Starter · #3 ·
Exhaust brake is off when I hear it.
 

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Sounds to me like it was in regen.
 

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Discussion Starter · #7 ·
I had a feeling... With it idling for a few minutes, I figured it may have tried heating up the exhaust a bit so it was starting regen.

Would the extra fuel being dumped cause the truck to feel like it had more power?
 

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I'm not sure if it's a regen or if it is just flowing EGR. There is a throttle valve in the intake that chokes off the fresh air flow, thereby causing a low pressure condition in the intake manifold. This, in conjunction with a closed position on the variable geometry turbo enables the exhaust gas to flow from the exhaust manifold, thru the EGR cooler, and into the intake. When all of this happens at idle I've notice my truck has a hollow deep sound.
 

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It is flowing EGR if you look under the hood when this is happening you will see the EGR bypass moving. If it was regening while the truck is stationary the whole thing would shake. not to mention the car next to you would be pretty pissed that you have 1000 degree exhaust gases aimed right at you. To my knowledge everyone learned from Fords mistake, and wont let a truck regen at idle. I know for a fact you can regen a cab and chassis with the starscan while stationary at about 2500 to 3grand constant to get the exhaust temps where you want them. The truck shakes like a though, so i prefer to drive it. I also tried it with a regular 2500 and it would not let me do it.
 

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Discussion Starter · #10 ·
Its a deep hollow sound so then it probably is the EGR... Also, I feel no diff in the smoothness of the idle.
 

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Discussion Starter · #12 ·
No chatter. Doesnt sound like any metal contact or anything moving. The sound is for sure coming from the tone of the motor.
 

· Robert Ivey
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maybe its the A/C kicking on and off....mines changed sound when it goes on and off..its not a 6.7...but it sounds possible
 

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My truck felt like it had alittle more pep off the line when I was in regen during idle.
No it was not at 1300 deg. at idle but it would stay about 600 or 700 deg.
 

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Discussion Starter · #15 ·
Mine doesnt really change sound with the A/C. Im thinking EGR since from what I have heard, Regen will cause a rougher idle. I have felt that before and from what I can remember, I dont think it changed the sound of the motor.
 

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Ok, Have just returned from dallas texas for training on the 6.7l and I have gotten to the bottom of this. It's actually called "net zero" the reason the 6.7 is much more quiet than the older trucks is that it has multiple injection events. think of injection as someone hitting a piston with a hammer. With one cycle all the force is used on one hit. The preinjection events are like tapping the piston before hammering it hard. It quiets the sound and makes it move a bit easier when the big blow happens. These trucks meet the clean idle standards so what happens is when you sit there and idle, the EGTs drop, and that doesn't help the NOX and DPF do their job.So it drops the second pre injection event to try to lessen the amount of unburned fuel. That in turn causes the louder idle, then in order to get the EGTs up it goes into high idle, and from what I am hearing after 1 hour of NO INPUTS (no doors opening< no brake or throttle inputs or anything of that nature) the truck will shut off. Its my understanding that either this was included in the latest flash, or will be in the next one. (anyone want to try it out to see?) The EGR flowing is also part of the process trying to burn that unburned fuel so as to create less DPF clogging soot.
 

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mine did that same thing you are describing until I did all deletes its the egr valve /egr actuator working I beleive. normal condition for stock truck but it will make you wonder what is going on
 
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