Sounds like spark knock

[RSZABO]

I am new to the 6.7 Cummins. My 2017 with 6300 Miles on OD. Just started making what sounds like a lite gas engine spark knock. Only happens when the engine is not working mid throttle.
Does not make the sound pulling or idle.
Seems like a predetenation sound.
Has anyone had this or have an idea where to start looking.
Thanks Bob

 

[sag2]

Just ignore it, there is nothing to repair.

 

[RSZABO]

Just ignore it, there is nothing to repair.

Thanks. Just seems odd, my 2000 5.9 or 2007 5.9ho never had it.

 

[Tuesdak]

You are hearing correctly a knock sound - Under some conditions the ECM may have too much timing that is trying to drive the engine backwards. It's a (likely harmless) design defect that would be ignored by the OEM's. Maybe a tune could correct it. Recall diesel has an ignition delay after being injected. The hotter things are the faster the diesel evaporates and lights off. So under some conditions the engine is hotter than the ECM is programmed for and the end result is a little too much timing. For a fixed "injection" timing the light off and peak cylinder pressure can change depending on the fuel and how heat soaked things are. 115 degree AZ is different than a cold MI winter day. Humidity even affects this: dry being worse than damp.

In experimenting with B99, biodiesel, our 2008 Duramax when towing a specific grade would ping/knock like this. B99 would change the sound. The condition was the Allison Trans lugging the krap out of the engine towing a specific grade letting the ECT run away past 235. Everything was getting heat soaked and this the ping sound would come on. It really needed to be in a lower gear for these conditions. There wasn't anything to tune in the base code to allow a downshift for ECT runaway, but, we did have it aftermarket EFI Live tuned to cut timing in that operating condition.

Now you know generally what is going on. I have read about others asking the same.

 

[RSZABO]

You are hearing correctly a knock sound - Under some conditions the ECM may have too much timing that is trying to drive the engine backwards. It's a (likely harmless) design defect that would be ignored by the OEM's. Maybe a tune could correct it. Recall diesel has an ignition delay after being injected. The hotter things are the faster the diesel evaporates and lights off. So under some conditions the engine is hotter than the ECM is programmed for and the end result is a little too much timing. For a fixed "injection" timing the light off and peak cylinder pressure can change depending on the fuel and how heat soaked things are. 115 degree AZ is different than a cold MI winter day. Humidity even affects this: dry being worse than damp.

In experimenting with B99, biodiesel, our 2008 Duramax when towing a specific grade would ping/knock like this. B99 would change the sound. The condition was the Allison Trans lugging the krap out of the engine towing a specific grade letting the ECT run away past 235. Everything was getting heat soaked and this the ping sound would come on. It really needed to be in a lower gear for these conditions. There wasn't anything to tune in the base code to allow a downshift for ECT runaway, but, we did have it aftermarket EFI Live tuned to cut timing in that operating condition.

Now you know generally what is going on. I have read about others asking the same.

This makes perfect sense, I am currently in hot humid south Florida. As the truck is under warranty, when I get back home to the mountains of NC I will see if the dealer has an updated flash that may better compensate for ambient temp. Since posting this while driving I try to either push the engine or feather the throttle at the speeds or engine loads when I heard the light knock. Making the engine work a little I never hear the noise.
Thank you for the info
Bob

 

[DonFitzwater]

Don’t bother. My 2016 did it at -30 in certain conditions.

 

[cerberusiam]

Typically, the timing curves on the 6.7 are much more linear and not ramping into the stratosphere under certain conditions. Normally do not get that type of knock unless something is wrong somewhere. If it is in fact knock form some pre-detonation or detonation it definitely is not good for the engine. Hard on rings and hard on pistons.

Knock when rolling into or out of the throttle or low shift conditions can also be TC bolts or DMF coming apart. Definitely something to monitor and get documented with dealer even though they may be able to find a solid source. If something does go wrong you have a paper trial documenting the complaints.

I would does it heavy with additives and try to find some premium diesel to fill with to see if that changes anything. It could also be just a bad tank of fuel causing a transient problem.