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So, maybe a dumb question, but I'll ask it anyway.
Car : 2002 Trans Am LS1/T56, 235,000KM
Spent the winter getting car back to a freshened up stock cruiser Just installed low mileage stock manifolds, Y pipe and Catback with new gaskets everywhere
New Denso O2 Sensors OEM air box w/ lower cold air pac, smooth bellow PCM was reflashed with 100% stock tune New updated PCV system in 2020 New intake manifold gaskets in 2020 New Delphi MAF (AF10056) New IAC New TPS
Has approx 70% fuel (Shell 93) from last Sept with fuel stabilizer. I had topped tank up with fresh 91 before this check
LTFT were at 0 as it was learning still (cars running fine). Had maybe 120,130KM on it. I did the EVAP service bay test to push monitor to ready - passed, and went ready.
Drove maybe 40Km to dinner On way back, got gas then drove 15Km and through on my cheapy scanner just to see STFT and LTFT This was what I saw maybe 15Km into that IGN cycle :
Got home, parked car, then checked KOEO and saw this :
Confirmed with Tech 2 :
Now, it seems a touch lean - but did LTFT adjust from 10x to 2/4 or is that LTFT different cause the cell its using is different?
I did put a new PCV hose from intake to PS valve cover (no leaks, but didnt feel "tight" on the connections (20+ year old rubber) and the intake manifold, took a good 2-3 turns on most of the middle/back bolts, they "cracked free" when I went to tighten, but took 2-3 turns to get to 89 IN LB. Now I assume that was my source of a +10% LTFT that seems global on both banks. I loosened all bolts in reverse order (just enough to release pressure, then did the 2 step torque sequence as per manual in order).
My main question is, depending when you check LTFT can it be different, or is this number the overall number?
Once weather improves Im going to get Tech 2 on it and drive a 70km drive to work, and back and watch STFT and LTFT to confirm.
My main question is, depending when you check LTFT can it be different, or is this number the overall number?
Yes, it can/will change depending on the fuel trim cell. So for direct comparison (over time), you'd want to check the percentage in the same fuel trim cell.
I wouldn't worry too much about it just yet if you found that the intake bolts were a bit loose. That is likely the source of an overall lean condition, so you can simply reset the PCM (or let it relearn over time) and see if the LTFTs settle into a range closer to 0. Anything +/- 5% or so wouldn't concern me at all with a stock tune/stock setup, honestly even a bit higher wouldn't really worry me in this application. +/- 10% is the threshold, on a stock setup, where I would start looking for possible issues - so you are right there but I'm thinking that the intake bolt re-torque was likely the solution.
Yes, it can/will change depending on the fuel trim cell. So for direct comparison (over time), you'd want to check the percentage in the same fuel trim cell.
I wouldn't worry too much about it just yet if you found that the intake bolts were a bit loose. That is likely the source of an overall lean condition, so you can simply reset the PCM (or let it relearn over time) and see if the LTFTs settle into a range closer to 0. Anything +/- 5% or so wouldn't concern me at all with a stock tune/stock setup, honestly even a bit higher wouldn't really worry me in this application. +/- 10% is the threshold, on a stock setup, where I would start looking for possible issues - so you are right there but I'm thinking that the intake bolt re-torque was likely the solution.
Same here, that and likely the older gas in there isn't helping. Ill throw the Tech2 on it and do my next few drives and watch
STFT dances around -3 to +3
LTFT averages are around 3 to 0
Nice to know after exhaust work this fall etc there are no external air leaks anywhere. Now to put some miles on it and recheck these averages after some actual usage
100% Be nice to get the storage gas out of it, and some months of driving to see what the Averages level out at!
To be honest, I don't think you'll see much change with fresh fuel in this case. If the gas is only ~8 months old and was properly treated with Stabil when still fresh, it's probably just fine still. My '98 rarely sees more than one tank of gas per year, so I always treat it with Stabil and it never runs any different when I finally get to fill back up with fresh gas ~12 months later.
But, either way, you might see numbers even closer to 0 as you continue to put miles on it. Stock tunes will often land the LTFTs anywhere in the +/- 5% range, so as long as you are in that window there are no worries IMO.
To be honest, I don't think you'll see much change with fresh fuel in this case. If the gas is only ~8 months old and was properly treated with Stabil when still fresh, it's probably just fine still. My '98 rarely sees more than one tank of gas per year, so I always treat it with Stabil and it never runs any different when I finally get to fill back up with fresh gas ~12 months later.
But, either way, you might see numbers even closer to 0 as you continue to put miles on it. Stock tunes will often land the LTFTs anywhere in the +/- 5% range, so as long as you are in that window there are no worries IMO.
Good to know, coming from a 99 spark table, long tubes and kinda a rough around the edges tune, it runs very nicely, little less seat of the pants with the spark reduction, but knowing its running as it should makes up for that!
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Understanding LTFT 
