L5P tapping/knocking noise when coasting???

[zf>allison]

Maybe this is why the cranks split in two pieces lol

[2004LB7]

I know on my LB7 and my LMM when I let off the throttle, as long as the wheels are turning the engine, the fuel goes to 0mm until just before idle rpm. Both show timing values but 0mm fuel injected

The LB7 actually has a DFCO (deacceleration fuel cut off) in the tuning. Haven't seen it in the later years but they seem to do the same thing when coasting.

[Awenta]

Yes the main injection goes to 0us when you let off until you're going slow enough that it needs help to keep running. Hm now I'm curious to see if there is any pilot injection going on at that time though.


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[RPM Motorsports]

Originally Posted by zf>allison

Maybe this is why the cranks split in two pieces lol

Or opposite, and they do it to throw off steady harmonics that cause crank breakage.

[THEFERMANATOR]

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.

[zf>allison]

Originally Posted by RPM Motorsports

Or opposite, and they do it to throw off steady harmonics that cause crank breakage.

Yes probably more likely. Sucks it's so noise on the newer truck like that. That's gonna suck in like 20 years when I can afford one.

[OregonDMAX]

be interesting to see all of korys customers breaking cranks after he "fixes it"

[Duvel]

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).

[jlawles2]

Let me know what they do to get the high idle in it. Dealer told me they could not flash the high idle in to it.

[WVRigrat05]

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.

[M.A.M.]

Interested in the high idle flash as well...

[Duvel]

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]

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]

Originally Posted by THEFERMANATOR

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]

Originally Posted by kiwilml

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. 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.