Duramax Diesels Forum Truck of the Week
Old 02-26-2017, 11:09 PM
Awenta's Avatar
Awenta Awenta is offline
Join Date: Sep 2014
Location: CT
Posts: 4,077

I'd like to see this on marks dyno measuring cylinder pressure

Sent from my iPhone using Tapatalk

2003 CCSB LT LB7 deleted

Some cool stuff, some fast stuff, some slow stuff
EFI by Kory

Special thanks to Evan@Limitless
Reply With Quote
Old 02-27-2017, 08:18 AM
DAVe3283's Avatar
DAVe3283 DAVe3283 is offline
Heavy & Slow

Join Date: Sep 2009
Location: Boise, ID, USA
Posts: 2,892


I think you guys are giving GM way too much credit. Having looked through a bunch of stock Duramax and LS tunes, I think GM gets it close, then phones it in once it passes emissions and makes their power target. The stock LB7 tune is a hot mess, especially the early ones.

I don't believe this was done to protect the crank. The amount of fuel is way too low to do anything meaningful. Plus, think of the shock loading the moment you step on the throttle after exhaust braking down a hill. It goes from ~0 mm3 to 40+ instantly. That first cylinder will have a huge differential loading vs the rest (which are still at 0).

I have noticed a recurring theme on stock Duramax tunes that might explain this, though. GM has had the timing for low fuel amounts (0-5 mm3) set really high since the beginning, and what this does is cause a "growl" as the transmission downshifts, especially in tow/haul. My dad (and probably lots of others) really, really like this sound on the downshift. I've played with the timing in that range, and the only thing it seems to do is change the note of the growl. I'm guessing GM did something similar on the L5P, and it isn't supposed to happen except in tow/haul.

Not that anyone asked for it, but that's my

Reply With Quote
Old 02-27-2017, 09:47 AM
2004LB7's Avatar
2004LB7 2004LB7 is offline
Join Date: Dec 2010
Location: Norcal
Posts: 1,352


Yeah, I doubt GM did this for a "growl". I think the best guess is what the ferm mentioned on crank harmonics. It make sense, they only need to inject just enough on random cylinders to upset the harmonics nothing more.
2008 Chevrolet 3500HD DRW LTZ
285/75/17 Nitto Dura Grapplers, 4.56 gears, Front and rear ARB lockers, Efi Live tuning by me, Raptor 160 LP, Cognito 4-6 NTB Lift, 4" Exhaust, Built Trans by Mike L.

2006 BRM Jetta TDI. Injectors, turbo, Malone custom tuning on ecm and tcm
Reply With Quote
Old 06-17-2018, 04:07 PM
JoeyD's Avatar
JoeyD JoeyD is offline
Join Date: Apr 2008
Posts: 51

My 16 van does it and was concerning but I guess not.
16 LGH Savanna
98 6.5 TD Pro Rok 60 front, ARB's front and rear, 4.56 Gears,37"KM2's
Reply With Quote
Old 06-17-2018, 06:10 PM
Hambone's Avatar
Hambone Hambone is offline
Always learning
Join Date: Jan 2016
Location: Florida
Posts: 462

Well seeing as this thread popped bag up figure Iíll update it with a bit of info...my buddy and fellow coworkers Ď17 3500 dually with a flatbed and welding setup was making a weird ticking sound following rpm at idle in park/drive
Poured some sea foam in the tank and didnít notice any changes
Turned out to just be in a weird regen cycle we havenít noticed before
He also had a leaking rear differential seal that warranty fixed
2017 2500 CC/LB "L5P" WT

2005 2500 CC/SB "LLY" LTZ
Typical mods for Longevity
awaiting stuff to go BooM then replace with more go fast parts!

And a few other retired Duramax's
06 360k aka Hog truck
07 320k aka Shop truck
07 340k Flatbed spare welding rig
Reply With Quote

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT -7. The time now is 09:19 PM.

Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2018, vBulletin Solutions, Inc.