L5P tapping/knocking noise when coasting???

Duvel

New member
Aug 7, 2016
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After a few calls and emails to GM, they still can't give me an explanation. They urged me to take it into the dealer if the drivability declined. I have an appointment with the dealer in Thursday to get the high idle flashed into the computer, so I'll run the "knocking" sound and the timing advance by them then. I have no problem putting up with the noise as long as GM will tell me "Yes it's supposed to be there, no it's not hurting anything, and it is there for 'this' reason." I don't think that's too much to ask(I'm not holding my breath though).
 

WVRigrat05

Wound for sound
Jan 1, 2011
3,081
4
38
36
French Creek, West Virginia
I've been trying to get high idle in mine for 3 years, ridiculous it's so hard to find someone that has the knowledge to deal it, I guess there's more to it than a simple BCM flash but I don't know.
 

Duvel

New member
Aug 7, 2016
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1 hour and $150 later, the high idle is now on the truck. I also showed the timing graphs to the service manager and he was making a call to GM as I left to find out why they timing advance and therefore "knocking" is programmed into the truck.
 

kiwilml

Member
Nov 4, 2015
454
0
16
So now you can be in park and set cruise and ramp up the rpms or what you talking about? Different than elevated idle correct?
 

catman3126

Ehhh?.... You don't say?
Jul 24, 2012
2,636
0
36
NE Oregon
When you're in a situation where the ECM is coasting, it will cut fuel. Even though your scanner may show 0 fuel, sometimes it will be enough for it to activate the pilot tables. It's supposed to take .016 of main injection iirc for the ecm to activate pilot for a stock lb7 i believe. So just because you show 0 on the main, it doesn't mean the pilots not active as I have 1st hand seen pilot come on while it showed main as 0. Also I know at least on mine, unless the converter is locked, it will normally inject some fuel even on decel. GM may have also made it try and keep fueling active for longer to try and keep it smoother on decel. Going to have to datalog one to see what is going on.


I figured it was Pilot not main causing this too.
 

Duvel

New member
Aug 7, 2016
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So now you can be in park and set cruise and ramp up the rpms or what you talking about? Different than elevated idle correct?

Yes, different than elevated idle. It's that $200 option you can select when you order the truck, but it only cost $150 when you have the dealer install it. :screwy: Just set the brake and hit the cruise button, it will idle up to ~1200rpm. Great for winter/summer long idle times and in conjunction with the heavy duty alternator package.
 

jlawles2

Well-known member
Jan 28, 2010
1,056
39
48
Danbury, TX
When I asked the dealer about installing it, they did not know. What did you tell the dealer to have them install the High Idle?
 

Duvel

New member
Aug 7, 2016
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When I asked the dealer about installing it, they did not know. What did you tell the dealer to have them install the High Idle?

I just told the service manager I wanted it installed. He called GM to make sure it could be done with the 2017 and he scheduled me an appointment. I'll take a pic of the paperwork when I get home tonight. They acted like it was a routine item, no problem at all.
 

Duvel

New member
Aug 7, 2016
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Here's a pic of the paperwork. Not sure it helps, but it's proof it can be done.
 

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DIESELMAFIAPER.LB7

<----new hotness
Jan 17, 2010
5,163
12
38
idaho
shop.dieselmafiaperformance.com
I tought this engine was more quiet? Could that be the reason that you can hear it now? I test drove one, I couldn't put my finger on it but I knew I heard something different. I will say it has good throttle response, it was quite peppy. I still think GM did something with the tuning on the 16 LML's bc mine has zero dead pedal, my 15's was so bad it was scary. I really didn't realize it fully until I drove that 17, it didn't drive any different than my 16. Anybody else with a 16 LML notice this???

My 16 isn't anywhere near as responsive as a l5p. L5p has much better low end and midmidrange response
 

Duvel

New member
Aug 7, 2016
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Just hit 1900 miles on mine. I'm loving it more and more as well. I came from a 2016 LML and I don't miss it at all. GM has really done a nice job with the L5P.

Still haven't heard back from the dealer regarding the knock. I'll give them a reminder call sometime this week.
 

TXGREEK

New member
Jan 28, 2017
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Just hit 1900 miles on mine. I'm loving it more and more as well. I came from a 2016 LML and I don't miss it at all. GM has really done a nice job with the L5P.



Still haven't heard back from the dealer regarding the knock. I'll give them a reminder call sometime this week.



Bought my loaded out 2016 a few months ago. I've been noticing a lot of concerns from both Ford and GMs new motors and trans. I'll give it a few more years for GM and ford to workout all the issues related to introducing their new redesigned motors and transmissions. I always recommend buying the last year of any model mostly because all issues have been for the most part resolved on a proven solid platform. Please please make sure to communicate with the manufacturer on all issues from the smallest to the major ones. Good luck


TXGREEK
 

TXGREEK

New member
Jan 28, 2017
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Competition, pushing out faster 0-60, pushing power over quality. It's very well known that all new models introducing either new or upgraded power plants take about two to three years to work out the kinks. Duramax, Power Stroke or Cummins all have their issues but will work themselves out, eventually.


TXGREEK