After Extensive E38 L92 Tuning, Gas mileage horrible and no power....

[raceghost]

Hi all,

My truck has been on the Dyno 3 times, with the addition of several road tunes, to the tune of a couple thousand dollars... I do both to dial it in. Extensive work because I have been there at all times. (Side Note: You might think I am crazy, but I had a 2004 Mitsubishi EVO 8 tuned to 630 WHP and 550 WTQ, getting 27 MPG on the freeway at 85 MPH...but I digress.) Originally, I was tuned on MAF only, and running on MAF only in my 2007 Cadillac Escalade EXT 6.2L L92 E38 non AFM/VVT. This tuner is very qualified. This last go around, we followed the EFI suggested tuning methods -->(here). Tuning entirely ALL VE first with no MAF, and then switching over to MAF again after that and then blending back to stock settings at the crossover point of 4000 RPM's. We also Load Dyno'd with simulated 8K towing. Truck lost power says the butt dyno, pulling a 3500lbs. trailer on the freeway. ON Maf only previously was avg. 14 MPG towing. and all around MPG of 14 as well. Post tune, running 12 mpg in town and 8 mpg towing only 3500 lbs....

Truck mods are:
Completely stock 2007 L92 non VVT with approx. 8K miles on it running E38-ECM. Fresh Rebuild, and broken in properly
Completely stock 2007 6L80E with approx. 8K miles on it running T43-TCM. Fresh rebuild and broken in properly
3.73 Axles with adjustments in rom accordingly. Stock are 3.42's, needed new so decided to give it a little more bump.

Everything Mechanically in the truck is new, I'm into it Parts to the tune of 25K... right down to the motor mounts.

AFE Cold Air Intake
JBA Shorty 1 5/8 headers
Magnaflow High Flow Cats
3.5" Full Catback with Magnaflow straight through shorty muffler with pre Axle dump
Always run 91 pump

Makes no sense.

Edit: Step by step view of tuning order:
After complete mechanical rebuild, first couple road tunes were for MAF only, since mods at the time were just CAI and Catback Exhaust
Then Dyno tune tuning MAF and Spark Tables only, no VE tables.
Added Shorty Headers and High Flow cats, since both needed replaced.
Road tune for MAF only
Then Dyno tune for VE since reading that headers seem to change VE decently based on several posts within this forum.

Note, I did the Dyno tune for VE because I wanted to do it right, and was only running on MAF using the Airflow switch set to 100 RPM's....

Edit: So on the dyno, the fuel tables for VE were saying the vehicle needed +15%-20% fuel in most of the RPM range...? Asked multiple mechanics if adding shorty headers would increase VE that much to demand that large of an increase (15%-20%) fuel? Most think 5% VE increase would be the max. So what measurement of VE being increased 1% demands what % increase in fuel? Meaning, if VE changes 1%, is that increase in VE of 1 require what measurement of increase in fuel? Put another way, an increase in VE measurement demands what in fuel measurement?

Also worthy of noting, our calculated MAF Table in the tune file with V2 in its label, was within 1/2% or .5% post V3 tune file. So after we spent several hours on the VE tuning, MAF was hardly out of range.

Any thoughts? If you need more info, just ask.

Thanks in advance.

Edited to include current tune, with my small adjustments for tires size, speedo, AC on and off with RPM, etc. Ignore the name, for it only relates to how I keep track of revisions, since we have some 45 for this truck. Map with V3 in the title is the latest fresh off of the Dyno 4.23.2021. Also include the last revision with V2 in title which is pre 3rd dyno which made 338 WHP and 387 WHTQ from the 2nd dyno time and several road tune hours. No Ve tuning in V2.