2013 Camaro LS3 Decel Fuel Trims

[Mike Norris]

I have a 2013 SS with a manual trans and when on decel in neutral (clutch in or out) it will idle okay and then start surging. When it starts surging the fuel trims go to 30-ish positive just before it happens. If I force Open Loop it will idle fine. In the data log you can see the fuel trims go instantly positive and starts surging at the 5:37 to 5:40 minute area on the time stamp. I have done quite a few cars and never seen this before. Any help is appreciated and thanks in advance.

[Gpargament]

I am not an expert but will do my best to offer some advice from personal experience. I am sure you have noticed your Cylinder airmass, map, spark, and rpm all fluctuate like a roller coaster. Your LTFT stay pinned for the entire surging. You dont monitor as many PIDs as i do, but i would be curious what is controlling fuel mapping during those times, also curious if DFCO/CFCO are engaging. You are a 2013 but your DOD is disabled, did you remove it? i thought your year had DOD. I also see your spark smoothing is off, i dont think that will fix it, but i was surprised to see it. Your spark actually matches your coastdown spark table, as your cylinder airmass jumps up and down, your spark follows with huge jumps of 25-30 degrees, this is reflected in your rpms, and hence you are enjoying a large and noticeable surge.

Thats my analysis and my guesses are this is within the tune, and not mechanical. I am unsure why your LTFT is set to only engage when your coolant temp reaches 275 degrees farenheit(which if it does your car is dead lol). the fact that open loop removes these issues, lets me know there is settings within the closed loop AFR management and its either out of tune, or bouncing between different spark controllers, like from base spark to idle base spark. I would look carefully at the tune, especially if you have mods.

Easiest fix is go SD mode and run open loop with fuel trims lol. the correct way or recommended, is to reset the tune and start over, something in that tune does not match the car's setup. Do you have mods? do you have dod? have the fuel trims been dialed in, they look all over the place? if cammed did you reduce spark to stop surging and smooth out the spark table?

Hopefully these questions and assumptions will help lead to your solution

[Mike Norris]

The cylinder airmass is steady at at the point where the fuel trims go from steady to positive 29% (5:36 in) and the only other thing that cahnges at that point is the timing goes from 19 to 16 degrees which appears to be a TM spark change per the log. The surging does not start for another 2 seconds as it takes a little time for the richness (29% positive fuel trims) to start causing it.

So I am trying to find out why the fuel trims jump almost 30% positive at that point on decel. Everything else seems good.

Mods are a decent cam (225/235 112 as a guess), cold air intake, FAST 102mm intake (not a fan) and stock throttle body.

Hopefully this more information helps.

[GHuggins]

Usually it's either the VE or transient fueling that causes this. Since you haven't tuned the VE, I would start there.

[Alvin]

You'd have better luck if you tuned VVE also. It really makes a big difference.

In the meantime you can try disabling DFCO and CFCO. It often improves return to idle on bigger cammed cars.

[Cringer]

I have a 2013 SS with a manual trans and when on decel in neutral (clutch in or out) it will idle okay and then start surging. When it starts surging the fuel trims go to 30-ish positive just before it happens. If I force Open Loop it will idle fine. In the data log you can see the fuel trims go instantly positive and starts surging at the 5:37 to 5:40 minute area on the time stamp. I have done quite a few cars and never seen this before. Any help is appreciated and thanks in advance.

Seems like I had a similar rich decel issue...the fix would be to either disable DFCO, or leave it enabled and max out the values in these cells:
[ECM] 2513 - LTFT Idle Cells Enable VSS = 255 mph
[ECM] 2514 - LTFT Idle Cells Disable VSS = 256 mph

However, have you dialed in your idle? 12 g/s idle and 24* of timing seems really high (for that cam) and that might also be a factor in the surging.