2011 Silverado Backfiring at Idle

[marasjm5]

Hello, after rebuilding the engine on my 2011 Silverado, I'm having some pretty wicked backfiring out of the exhaust. I don't have a lot of experience tuning, and I'm not exactly sure where to go from here. I would highly appreciate it if anybody could point me in the right direction to solve the issue. I'm running speed density. Below is a list of most of the specifications and modifications done to the truck.

LC9
243 heads
15cc dished 3.785" piston
8.4:1 compression ratio


Duration at 050 inch Lift:
232 int./234 exh.
Advertised Duration:
281 int./286 exh.
Intake Valve Lift with Factory Rocker Arm Ratio:
0.600 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio:
0.575 in.
Valve Lift with Factory Rocker Arm Ratio:
0.600 int./0.575 exh.
Lobe Separation (degrees):
115

Camshaft features base circle of 0.720 int./0.735 exh.

vvt delete
afm delete

Aeromotive 340LPH fuel pump

750cc injectors

speed density with 2 bar MAP. IAT relocated to the intake manifold.

AEM 34-0334 wideband

7875 turbo, intercooler, single scroll log manifold, 3" downpipe, 3000 stall converter


I've attached several files: the stock file, my current tune, an Excel spreadsheet of my fuel injector data, and a short log file. I don't have my scanner optimally set up, and I will be taking some time to get that properly set up before I run the truck again. sorry about that. The truck idles decent enough to run on its own, but I can't run the truck long due to the backfiring. Because of the design of my exhaust, it's insanely loud, and I'm afraid that the police might show up in response to what they might think is gunfire. lol.

I haven't done much to adjust my ignition timing yet, nor have I adjusted my fuel injector timing. The next thing I'm considering adjusting is my idle over/underspeed spark, and I'm considering adjusting my fuel injector timing using a spreadsheet that some others have used. I just haven't found much information regarding those parameters, and I would prefer a little more education before I take shots in the dark.

On a side note, I do regret my choice of turbo hot side. I'm sure I will upgrade it in the future, but for now, it is what it is. I'm not exactly sure what the best way to go about my upstream 02 sensor placement is, considering B2S1 is just before the T4 flange and reads exhaust gas from both banks. B1S1 is in the cross pipe, Wideband is in the downpipe. If anybody has a recommendation on how to best go about that situation, short of replacing it with a twin-scroll manifold, I'd appreciate it. I've kinda been hoping it'll just be 'good enough'.

Thanks for your time!

[Alvin]

This looks like a regular miss to me. Look for a cold cylinder at idle. I do not think this is tuning related.

[marasjm5]

10-4, I'll dig into it a little further. Thanks!

[marasjm5]

So, to update:

Today, i spent some time on the silverado. I had double checked my wiring prior, but I had missed the fact that I swapped a couple wires on a couple ignition coil plugs after repinning the harness earlier. It was a mistake and im kicking myself over it, but I'm glad it was a simple fix. I swapped the wires around and it runs much better with no backfiring.

This was a kick in the right direction which made me slow down and go back to the basics. I was so sure that my wiring was correct after checking it more than once, but I was wrong. Mistakes happen.