How often do your ltft change? On my last car (eclipse) they moved VERY slowly. Took a while to get them to change. On this 99z they move almost as fast as the stft.

 

In open loop they really shouldnt move at all, depending on your tune. However, under idle yes they will flux almost as much as your stft. But the more consistent you are on the gas they should level out.

 

It depends where your STFT are at, how stable the
tune (and its sensor inputs) are. If the STFT are not
able to do the job and drift up there then they will
start to drag the LTFT along pretty quick. If STFT
stay positive all the time then they will accumlate
more than when they swing + / -.

Problems like O2 sensor laziness destabilize the trims
and make a "driving history" element to the trims.
So does having FTC cells that cover too much and
too non-regular of an operating region (like idle to
2500RPM, two ends of it nothing alike on a cammed
car).

Too smart for its own good, perhaps. If it's trying to
follow a bouncing ball, guess what? Bouncey bouncey.

LTFTs moving around much at all means you're not
done.

 

The movement in LTFT's that you're seeing might be because you're switching between fuel trim cells. There are seperate areas the pcm learns fuel trims...like idle in park, idle in gear, low map/low rpm, medium map/low rpm, and so on. Day to day variations can usually create a ~2% change in LTFT's. I see the most drastic change in fuel trims after I fill up for gas. I think it has to do with the EVAP system. Either way, the more drastic the STFT's are swinging (further from zero), the faster the LTFT's will update.

 

If they were moving just a little bit I would not think much of it. For the majority of the time they are between -1 and 1. Then it will jump up to like 10.4 then back to -6.7. I dont get why it would do this. The 02 sensors are less than 8k miles. Anyone have any idea what should be adjusted to fix this?

99Z A4 lid, magnaflow, 3.73, and hpt

Thanks

 

I believe SSpDemon answered this question when he said "The movement in LTFT's that you're seeing might be because you're switching between fuel trim cells". You need to datalog and pay attention on playback to see if the fuel trim cells are changing right when the LTFT's change that drastically. The key is to datalog so you can pinpoint exactly when and where it happens. Then you can adjust accordingly.

 

Just finished a TransAm with ST and LTFT jumping around at idle and cruise due to the supercharger causing a lot of air turbulence in the MAF, thus the MAF sensor's signal was erratic causing this. Hard to tune for good drivability with some of these combinations.