So check this one out. Just finished up a project on my '12 GT replacing the entire drivetrain; McLeod clutch & billet lightweight flywheel, Calimer state 3 tranny, DSS one piece driveshaft, completely overhauled axle with 3.73 gears (from 3.31). Yes, did the crank relearn (car is Lund tuned). The car now has little to no engine braking. Lund has provided three tune updates now that have not changed anything. Car runs 100% absolutely bonkers amazing. We touched nothing on the engine this project (other than the new files to try and address the loss of engine braking). I've attached a video of a pretty mild pull to 4K in 2nd or 3rd gear and then let off the gas. Very little braking and tons and tons of pops and crackles. It never did this before the project. Any ideas?!?!?!

Is the crackle part of the tune? Taking a total stab here. Excess fuel on over run, rather than fuel cut on closed throttle normally, with timing still firing before exhaust valve opening sufficiently to dump gases out exhaust. You are still building compression and therefore drive.

Like GAR944 said, normal OEM behavior is that the fuel injectors actually shut off during off-throttle coasting in gear. You can hear the transition when the exhaust gains that subtle deeper rumble (it takes a mere moment to kick in once you get off, so you can hear the transition). The high compression with no combustion then leads to engine braking.

I get it, but what caused it? What caused the change? Nothing on the engine/tune was touched.

No, the pops and crackling is not part of the tune. Same file as before the drivetrain.

In your OP you state the car is Lund tuned with multiple file revisions?

galaxy said:

Yes, did the crank relearn (car is Lund tuned).

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galaxy said:

Lund has provided three tune updates now that have not changed anything.

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galaxy said:

We touched nothing on the engine this project (other than the new files to try and address the loss of engine braking).

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Since you said you did no hardware modifications to the engine that require tuning, flash the stock tune back in and see if you get Deceleration Fuel Shut Off behavior back.

The multiple file revisions were only to try and address the new issue. None worked. To clarify, the tune file that’s been in the engine for the past two years running amazing was not changed when these new symptoms started after the new drivetrain. I did not swap a file tune in conjunction with the new drivetrain install.

So to start troubleshooting, does the behavior continue when the stock OEM tune file is loaded back in?

I suspect it’s the combined effect of a lightweight flywheel, clutch, and driveshaft, all of which reduce rotational inertia on the engine, plus the 3.73 gears which are forcing the engine to slow more quickly. All of that combined might make the crackles and pops worse? But I don’t understand the no engine braking….. if anything I would think you’d get more engine braking with those mods not less?

I'm in the datalogging process with a fresh Lund tune I have... no snap, crackle, pops for me. Engine braking seems the same too.
That totally sounds like a popcorn tune!

I've gotta think something is off about the crank relearn. Maybe try it again -- with some different software maybe. If you used SCT tuner last time you could try FORScan this time...

Back when dinosaurs roamed the earth and I had a supercharged 2011 GT track pack, I did a lot of tuning work on the car myself using the SCT toolset.

One of the things I recall, vaguely, is that the OEM tune holds the throttle slightly open and pumps fuel through the injectors when you're "on the overrun" (engine braking). The reason they do this is to keep the cats from cooling off when you're going down a long hill. Now, I'm not 100% certain, but I think that function is controlled by a switch in one of the settings tables. It's possible that the overrun switch is in the wrong position. Now, how it got that way if you didn't install a new tune after the driveline work, hard to say. Might be worth checking with Lund.

It is 100% not some popcorn or intentional crackle tune.

Thanks for the tips so far. Will try. Still doesn’t make any sense, but will try.

The crank reset was done with a NGauge. Still have one that has the feature. I don’t have the full forscan version to do it at home. Would have to hit up a dealer. How different is forscan/dealer from what the NGauge is doing?

As a big fan of aluminum flywheels I'd say stevbd is prolly on point. I've seen this occure after changing out the iron lump. There's still some braking, just much less than you're used to.

Which doesn’t make sense since all the light weight components should be more engine braking.

galaxy said:

Which doesn’t make sense since all the light weight components should be more engine braking.

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How do you figure that?

Heavier components (iron flywheel, etc) when spinning at rpm, have substantial momentum to keep the rotating assembly spinning. Remove that, let off the gas, the engine should slow down faster. Was previously mentioned above.

As a reference point, I have an ‘11 with similar lightweight components but with FRPP procal tune and 3.31 diff, minimal crackles and pops. It does seem there’s a tune element to this? What is your exhaust system?

kooks long tubes, Kooks high flow (not green) cats, Kooks x-pipe, and Borla ATAK mufflers. The pops and crackles are not the problem, they are a byproduct of the problem - the no engine braking. Nothing on the exhaust was changed in conjunction with this drivetrain project. But they certainly are annoying at the moment.