Re-scale MAF results in major MPG loss.

[Stonewall]

OK I've done the VE tune and re-scale MAF to get LTFT's in line but at the same time my MPG's have dropped by 3 mpg's. What is going on here. I admit I'm going off the wall running a 05 PCM in a 06 car but my choice is limited.
My question is why dialing in LTFT's would cause increase in fuel useage. If I run stock my LTFT's are -10 to -12. As soon as I start dialing these closer to zero the MPG's go down. Why is this? Any help would be appreciated.

Edit for typo: The mpg's have dropped by 3 not 6 as original post. Was at 26mpg now I'm at 23.

[TDCRacing]

What are you baseing you mpg info from? if its the dic it's not as accurate as you think. unless you have added more fuel via the maf ve table ect. you are not actually using any more fuel.

[5_Liter_Eater]

How long a period are you measuring. If you reset the trims and they need to get back negative it will take a little time to get there and until the trims stabilize you may be running a little rich.

[Stonewall]

Thanks guys. Yes I think your right about the trims. I was watching the DIC over a drive to work. I was doing a compare on a known route but I did reset the trims after changing the MAF table and the trims have not settled in yet so that very well could be the decrease in MPG. I'll keep an eye on it and see if it gets better.

[Trannyman95]

The mpg is only closely accurate if the fuel trims are as close to zero as possible and this is part of the calculation the pcm uses to show mpg data. I learned this a long time ago when installing larger injectors before pcm tuning was available for self users to tune. I installed 42 lb/hr injectors in my L67 engine and my high way mpg went from 30 up to 39! This was the only change made and then I realized my fuel trims were very negative. Once I purchased HPT when it first came out and got everything back in line the driver info center again read properly. I wouldnt strictly rely on it and always check your milage at the pump to compare as I have found many scenarios where the info center is not spot-on, especially if your fuel trims vary too far at all from zero.

[Stonewall]

yea trannyman that makes sense. I have never used the DIC reading as reliable, only as a compare. Thanks for the reaply.