LS3 480 W / Headers Help needed sounds like a diesel

[RobG8LS3480]

I got a new crate motor ls3 480 for a 2009 G8 and took it to a tuner in fort worth and it sounded a bit off with too much engine noise when I got it. Still sounds bad, so I took it to GM dealership since GM performance motors come with a warranty they said they did not hear anything that specifically sounded bad. So I have been trying to find the sound and diagnose. I got HPV12 but no wide band and created some logs and downloaded the tune to look at it. Not sure what I am looking for. But long term fuel trim was disabled, cot was disabled. So I have enabled to see what the trim was and it was +10 + running lean I have tried to adjust but the sound is the same. No wide band yet. Just want it to run right so I can drive it.

[RobG8LS3480]

Trying to attached tune and log I have.10-14-timing-4deg.hptvideo log 10-14 warm.hpl

[5FDP]

LTFT and COT being disabled is very common with headers and aftermarket cat converters. It's easier to calibrate with a wideband and fine tune the STFT to dial everything in. COT is there to enrich the fuel mixture to help protect the cats and really isn't something that you have to keep on. Most also disable it or set it to the same value as the power enrichment EQ ratio because the enrichment value causes the fuel mixture to go much richer than PE is set for.

That log you post looks good to be honest. Can't tell if that was just at idle or if you were moving because MPH was not logged but overall it looks good. The tune is also pretty conservative and that is a good thing.


It's hard to comment on the "sounds bad" without a video of the issue or a far better description of the noise. Just remember that you have headers and if those headers are cheap thin steel, they will make tons of noise from the valve train. Higher grade headers or coated/wrapped headers will make less noise.

[RobG8LS3480]

Thank you for taking a look. I had the noise before the headers and did the headers because of the noise thought it could be exhaust leek.
I will work on editing the video and post a part of it. I will check the COT EQ ratio too thanks.

[RobG8LS3480]

FYI, I was told the LS3 480 hot cam is noisy too. So last week I disconnected the transmission to eliminate it. Headers are StainlessWorks brand G8 headers. They changed the sound but not the part I am talking about. Sounds like piston slap but only when warm. The rpm were maybe a little rev at start and finish but mostly driving down the road mild acceleration I hear it most when everything is quiet in car windows up no or low road noise, low speed no fan and go from 1000 to 2500 rpm. after that you can not hear it but I think it is still there. same if you drive with radio on or over 30 mph or windows open can not hear it. from above engine you can hear on driver side sounds like number 5 cycl. What is the best way to start diagnostic for engine noise ? brand new ls3 480. Warranty maybe void since I installed at home with a friend certified mechanic friend. At idle I can hear but not as bad sounds bad like a diesel in that range 1250 to 2500 rpm mild acceleration. Was hoping it was something in torque management that should not be there causing too much fuel or spark advance. I turned down spark advance by -4. so any help is greatly appreciated.

[RobG8LS3480]

Update I was looking at the log attached I noticed the map of 45 or 50 and 2000 rpm in my table is 15 spark advance deg. but my log shows 30 spark advance deg. so now i am trying to find where the extra 15 came from. modifier or multiplier somewhere.

[RobG8LS3480]

UPDATE Found the LS3 480 has bigger injectors than the LS2 and the flow rate tables needed to be set before any other tuning or driving to be honest.
Just now a year later running better. But I had found one table for injector flow rates that was like all numbers were the same. Better but not right.
and found one for LS3 480 that had better curve but was for different points / axes. Some conversion required. Only drove it a few times since working from home but so fun to drive now. Can not wait to get it better.