LTFT, B1 consistantly higher than B2. Common?

[Michael_D]

Just curious. LS7. Fuel trims on B1 are, and always have been, about 3% higher than B2. It is more consistent under 2500 rpm, but runs slightly higher above 2500 as well. Before I start tearing stuff apart, to try and find something mechanically wrong, I got to wondering if this was common.

[SultanHassanMasTuning]

leak?

[Iam Broke]

It was that way on my LS1 and is 2-3% on my LS3 as well. No leaks.

[SultanHassanMasTuning]

i personally would not worry about it at all

[Michael_D]

I had thought of a leak, but no, I could not find one. I'm leaning towards a flaky O2 sensor. After looking at a few log files a bit closer, the left bank output has a few weird drops on the graph table. It will show a random abrupt drop, not a sweeping arc like normally shown on the log. Sometimes, these drops will only dip about half way, then shoot back up.

I did however tear the heads down yesterday. Excessive guide clearance already after 5K miles on rebuilt / ported heads. I knew I should have just ran a rail set up with roller tip with this cam (.670"). I doubt that was the cause of this miss though....

Is there a preferred brand of O2 sensor?? The OE is Bosch correct? It looks like there are also sensors made by Denso, Walker and NGK.

[camONLYls1]

I had the exact same "issue" with my '07 z06. I bought the car in 2012 stock (Haltech MF103) with 12,3xx miles on it. Replaced both O2 sensors just in case, especially since bank1 would abruptly "swing" like yours. I saw no difference with the new brand O2 sensors from GM (not sure of OEM brand). Since then, I've replaced the exhaust with LT headers and a catless Xpipe. I still to this day have the same "issue", but no exhaust leaks.

I know this isn't too helpful, but at least you know you're not the only one.

-Shane

[Iam Broke]

Pretty sure it's typical on the LS engnes, that's why most recommend putting the WB for tuning on B1 as it is usually leaner.

[Michael_D]

Interesting. ..... I cannot see a reason why the left bank would run leaner. I'm yanking the intake and heads.

[LazMan]

I used to have a 2006 Pontiac GXP which I bought brand new. Since day one it displayed the same issue, and always did until the day I sold it.

I have a 2009 Pontiac G8 GXP with 59300 miles, and I bought it brand new. Since day ONE I've had the same issue with bank 1 being consistently 1-2% leaner than bank 2. LTFT were always 0.8, 1.6, or even 2.4 higher. I've tuned it such that bank 1 is as close to 0 as I can get it and bank 2 is consistently -1.6 to -2.4.

This is still the case today, and nothing I have done ever changes that, and after reading now and again the same thing being posted and/or asked by others, I've accepted that this is just be the way it is for LSx engines.

[07GTS]

dosnt it have to do with the firing order between the two banks, where one bank has two firing closer together then the exhaust will have a richer environment for a little longer than the other side that might be more even and since idle is so slow it picked up by the sensors, just a thought thats all...

[Michael_D]

Hadn't considering that. Cylinder 6 fires after 2 while all other fires alternate bank to bank. Hmmmm.... I freely admit that I do not know what I do not know.

Well in my particular case, fuel trims are consistently 3% higher on B1 than B2. That seams a bit too high, when considering that according to all the different "how to tune" books I have say to get AFR error under 3%.

[MikeOD]

Hadn't considering that. Cylinder 6 fires after 2 while all other fires alternate bank to bank. Hmmmm.... I freely admit that I do not know what I do not know.

Well in my particular case, fuel trims are consistently 3% higher on B1 than B2. That seams a bit too high, when considering that according to all the different "how to tune" books I have say to get AFR error under 3%.

And cylinder 1 fires right after 3 on the other bank...1-8-7-2-6-5-4-3-1-8-7-2-6-5-4-3-1-8-7-2-6-5-4-3-1-8-7-2-6-5-4-3-1-8-7-2-6-5-4-3...it's a loop.

[8850]

Disable LTFTs and the VE table. Run mass air only, problem solved.

[Iam Broke]

Na, the STFT's will still be 2-3% higher on B1. I run a MAF only tune.

[Michael_D]

Well I pulled the heads and found excessive intake guide clearance. The valves are coated with oil and the combustion chambers and pistons have a thick carbon layer. I suspect this is part of the issue.

[Iam Broke]

Both heads or just Bank 1?

[Michael_D]

Both, and ya, I know...

[Iam Broke]

You read my mind already.

[edge04]

Must be common. Don't you remember Nicholas Cage in Gone in Sixty Seconds "sounds like the left bank is lean"