LTFT values variance between trips

Car is a 2002 T/A with a 408ci LQ9 Iron block, MS3, T56, Longtubes, Fast 90/90, from Texas Speed. Tuned by professional tuner and it runs OK.

It was a while since I checked how the car was running after it was tuned, so I did a couple back-to-back data logs after warming up the car while driving around town running errands. Going to the last store I scanned on my way there, and then scanned a second time while returning back home. I was at the store only 5 minutes.

Log A shows LTFT's with inconsistent values in adjacent cells. Log B shows LTFT more consistent cell-to-cell, but very lean. If you compare some cells between logs, you'll see the trims are very different between logs. The driving pattern, traffic conditions, air temp was exactly the same because Log A is going to the store, Log B is returning from the store with only 5 minutes in between.

Why are the trims so different between one logs??

I have been tuning my maf and logging quite a bit lately. I have seen that happen before as well. The motor seems to be + or - 2% and then I get a log where it is 5% lean, then log again later and it is normal.

Can't really explain it but you may want to reset your LTFTs and log again before you trust any of that data.

Thanks, but it still doesn't explain why the variance. O2's are relatively new, it's a new motor w/new sensors and plugs. Less than 5K on the setup.

Any one else have an idea or two?

No one?

Paging WS6FirebirdTA00 or EC-Tune. Please give me a rational explanation, if you know one, maybe...

Heat soak will cause log data to read lean after a hot startup.

Quote:

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Originally Posted by EC_Tune

Heat soak will cause log data to read lean after a hot startup.

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That was my initial thought as well, although his IAT's and ECT's are functionally the same for both logs. Wouldn't we see a difference in one of these values if it was heat soak?

Thanks guys. But, like Rhino said, IAT and ECT were the same because the car was already at operating temp.

I had been driving to several places over a span of an hour prior to scanning. Both data logs were done going to the last store before returning home. Log-A on the way to the store and then 5 minutes apart, Log-B on the way home.

Any other ideas?

Quote:

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Originally Posted by EC_Tune

Heat soak will cause log data to read lean after a hot startup.

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I get the same thing. What should you tune for though? Is that why most try to tune slightly rich? LTFTs -2 to -5?

Thanks.