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Cummins HO Predetonation

AlphaOmega

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Hi all,

Been lurking here for awhile and just joined. Bought a 2020 3500 HO Cummins about 4 months ago. Had it to the dealer yesterday for belt/pulley chirp, and check engine light (which ended up being and exhaust sensor I guess). Anyway, they also reflashed my PCM yesterday because apparently there was an update. I've noticed a significant increase in predetonation/dieseling noise since I picked it up. Before it really only was happening when cruising at moderate speed and then speeding up. Now it is happening with pretty much any acceleration, even at highway speeds. Seems like the trans is shifting weird too, but I'm guessing maybe it has to relearn again. Anyway, this is my first Cummins engine. Previously I have had 2 Duramax diesels, which were super quiet, and quite responsive all the time. Mine has had what I would consider horrible turbo lag since I got it, and now the predetonation noise. Just wondering if this is normal for these engines or if I should be concerned about the reflash?
 
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Mine has some "timing rattle" mostly just off idle. Very quiet going down the road.
 

AlphaOmega

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Yes, that is what I would call it...timing rattle, predetonation. Was rare before the flash, and is prevalent after. I am wondering if they used the wrong flash. Was searching this site and saw a TSB on two different flashes depending on which CP4 version the vehicle has. This dealership is a combined GM/Ram dealership in a small town, so thinking maybe the tech didn't know that. I don't know, unless they get the update based on VIN, then it should be correct. Was just wondering how everyone else's sounds, as again, this is my first cummins.
 

flan

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With pilot injection Idle is quiet, start putting some fuel to the engine the PI goes away and you are hearing what a Diesel engine would sound like without it.
 

AlphaOmega

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So you are saying this is normal? Just asking. Didn't hear this with my Duramax in the past. Also, just to be clear, this is a predetonation sound, not the normal solid thudding sound of a diesel.
 

flan

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So you are saying this is normal? Just asking. Didn't hear this with my Duramax in the past. Also, just to be clear, this is a predetonation sound, not the normal solid thudding sound of a diesel.
Tough to say without a sound clip, but it’s my hypothesis at least. FWIW, I’ve driven a 07 Dmax and it was noticeable to me. Not sure which year you had. 6.0 fords, same thing.
 

dslbrnr

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I've owned two duramax's, three PS's and now on my fourth I-6 Cummins. The Cummins are always a little louder than the V8 diesels I've owned.
 

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