14 tahoe 4x4 poor fuel mileage help

[dirtymax6610]

I purchased a 2014 Tahoe 4x4 with the 5.3 and 6l80 transmission. Tahoe has 126k miles on it. Turned out that the engine was bad and so was the transmission. Did a complete rebuild on engine and also the transmission. With the engine had the heads redone at machine shop, full valve job and pac beehive springs. Using trunion kit from Texas speed. Engine was honed out, stock crank and rods. Using a set of silvolite pistons and a Texas speed stage 2 truck cam. The timing chain, lifters, oil pump, and remaining parts were all part of texas speed kit. Engine was dod deleted and vvt deleted . Intake is stock and resusing the stock injectors. New stock replacement throttle body, Texas speed 10mm wires, stock coils, e3 spark plugs and a set of dougs short tube headers. Trans was a stock rebuild but did the thermostat delete, bypass and a billet converter. With body off of Tahoe put in a new gm fuel pump, full new factory exhaust including cats and 02 sensors. Full front end rebuild including rack and pinion. Then tahoe was tuned by a local tuner. Has 22" snowflakes with 33"s . Engine was assembled by local machine shop as well. Stock 3.42 gear ratio.

Now to the point of all of this. This was supposed to be a good daily driver for the wife. When i was picking out the cam and other stuff from Texas speed i talked with there tech support on picking out my parts. There guy said they have done many of these builds with the stage 2 truck cam and they average around 23 miles per gallon. Since this build have put about 7 thousand miles on it and the best average fuel mileage is about 12.5 to the gallon. My question is am I not going to get the fuel mileage with this set up? Is there something im over looking that i need to change or is it simply a tuning issue. Im really at a loss with this thing. Her old 2007 Tahoe with the 5.3 and 4l60 with almost 400k on it got 16 to the gallon. I figured this would get better mileage period with just moving up to the 6 speed transmission. Any help or suggestions are greatly appreciated.

 

[B-train]

I'm not sure what to tell you, but in my experience when you deviate from OEM as-built specs, you're bound to have a negative change in mpg (not all the time, but there is usually a trade off for more power, etc). I'm not sure what affect the VVT delete has on these motors. There are MANY workings in the ECU on these motors that all need to work together properly.

Do you live in a cold climate? We're the catalytic converters deleted or replaced? What was the original issue that prompted thr rebuild?

 

[15burban]

The 33s aren't helping but just them alone won't hurt the mpg too much.

Just my opinion but never go off what someone else says for mpg and expect to get the same. Way too many variables for mpg's unless the person telling you drives the same exact roads as you at the same speed, accelerates the same, etc.

Could even be the way your wife drives. There is a thing called coasting that a lot of women and people in general don't know about it. If you see a red light up ahead you don't have to play the "how good are my brakes today" game and be on the gas til the last possible second to slam on the brakes and barely stop before you reach the intersection. Same with on the highway when coming up to a slower vehicle in front of you.

 

[Trey Hardy]

I purchased a 2014 Tahoe 4x4 with the 5.3 and 6l80 transmission. Tahoe has 126k miles on it. Turned out that the engine was bad and so was the transmission. Did a complete rebuild on engine and also the transmission. With the engine had the heads redone at machine shop, full valve job and pac beehive springs. Using trunion kit from Texas speed. Engine was honed out, stock crank and rods. Using a set of silvolite pistons and a Texas speed stage 2 truck cam. The timing chain, lifters, oil pump, and remaining parts were all part of texas speed kit. Engine was dod deleted and vvt deleted . Intake is stock and resusing the stock injectors. New stock replacement throttle body, Texas speed 10mm wires, stock coils, e3 spark plugs and a set of dougs short tube headers. Trans was a stock rebuild but did the thermostat delete, bypass and a billet converter. With body off of Tahoe put in a new gm fuel pump, full new factory exhaust including cats and 02 sensors. Full front end rebuild including rack and pinion. Then tahoe was tuned by a local tuner. Has 22" snowflakes with 33"s . Engine was assembled by local machine shop as well. Stock 3.42 gear ratio.

Now to the point of all of this. This was supposed to be a good daily driver for the wife. When i was picking out the cam and other stuff from Texas speed i talked with there tech support on picking out my parts. There guy said they have done many of these builds with the stage 2 truck cam and they average around 23 miles per gallon. Since this build have put about 7 thousand miles on it and the best average fuel mileage is about 12.5 to the gallon. My question is am I not going to get the fuel mileage with this set up? Is there something im over looking that i need to change or is it simply a tuning issue. Im really at a loss with this thing. Her old 2007 Tahoe with the 5.3 and 4l60 with almost 400k on it got 16 to the gallon. I figured this would get better mileage period with just moving up to the 6 speed transmission. Any help or suggestions are greatly appreciated.

That’s odd my 07 Tahoe with 400,000 even with a large vacuum leak and misfire would get 13.5-14.5mpg with a 9” lift and 26x14s on 35s
My 14” lifted Silverado on 14 wides and 35/15.50s would still average 14-15mpg

 

[Doubeleive]

I get about 9.5, the biggest factor is the big pedal, but she is not going to get 23

 

[mikez71]

His wife can't be driving badly to get 16mpg on their old tahoe!

Currently at 8.8mpg 8.7mpg, maybe somethings wrong..
but I frequently use E85 and all short city driving.. And I don't drive super slow..

But I find 23mpg a little hard to believe..

 

[Marky Dissod]

Engine bored out, VVT deleted ... neither of those things help MpG.
Find a different tuner, have him sit next to you,
while the laptop is recording realtime data during a lazy, low-load, non-enthusiastic drive.
It may not be a tuning issue, but this provide better info than we can come up with.

 

[Fless]

Look at the fuel trims with a scanner in live data to see if they're within an acceptable range.

What octane fuel do you run in it?

Is it being driven in 2wd mode most of the time?

 

[j91z28d1]

a lot of times guys quote highway mileage after swaps and mods. mainly because stop and go city traffic mileage goes to crap. especially if you have to idle a alot with a cam.


just for reference, if she drives it in soccer mom hell like mine, even the hybrid tahoe don't get real world 20mpg, especially summer ac blasting sitting in school pick up lines type of crap.


I think an honest real world daily city driving almost 13mpg is really pretty good for a cammed out truck.


but yes, check your fuel trims might give an idea.

 

[Doubeleive]

I bet i could get it down to 7.5 lol