04 Tahoe 20mpg goal

[Andrewhans]

I'm new to ecomodding anything, but my recent purchase of a 2004 AWD 5.3 Tahoe has me looking for ways to get over 20mpg per tank. It's rated at 13/14/17. I'm currently tuned for and running 93oct e10-e15.

I've changed my driving habits quite a lot... I do 50 most of the time, minimize my idle time, put the trans in neutral when coming up to stop signs and slowing down, accellerate quickly keeping rpm below 3k, load around 40% and keeping AFR as lean as the tune allows during accel(14.2).

Here's what I've done
-BlackBear Performance ECU tune (horsepower and mpg)
-OEM 05-06 Tahoe/Suburban front air dam
-Roof rack delete
-Synthetics in Front/Rear diff, trans, engine and transfer case
-OEM 05 Electric fan conversion
-75% grill block

I haven't really been trying/modding for gas mileage until very recently. That's why I joined this site to get the last 2-3mpg of my 20mpg goal.

On the very near horizon
-3" front 5" rear drop
-LED lights conversion
-Getting the ECU retuned again with better shift points and leaner cruise AFR
-Coroplast or aluminum bellypan

Ideas are welcome. Just as a heads up I'm near my limit for visual mods.

Andrewhans

[oil pan 4]

Make your self a bigger air dam or alter the factory one increasing its reach.

I run a lot leaner than 14:1 during part throttle light acceleration, I petal the carb for between 16:1 and 17:1.

I was able to get about 3 more MPG out of in town driving just doing EOC and turning the engine off when it wasn't needed.

[Andrewhans]

I would love to do EOC coasting but my brakes are powered by the powersteering pump and the auto transmission would be damaged due to lack of lubrication since the pump isn't spinning with the engine off. About the best I can do in that department is Engine On Coasting.

As far as the AFR's are concerned I will be sending the ECU in to get retuned for much leaner AFR's during cruise and shifting earlier under more throttle.

The air dam is currently 9" from the ground so after I lower it will be down to 6". Is it advisable to go lower than that?

[oil pan 4]

If that Tahoe has an 4L60E well then my longest EOC was 17 miles and it still works fine.
I have seen plenty of 4L60E and 4L80E transmission vehicles be flat towed over the years.
That myth appears to mostly apply to foreign FWD auto transmission cars.
I know I cant flat tow our auto transmission VW or Hyundai.

My diesel also has hydro boosted brakes and I EOC and brake all the time. The only reason to depend on power brakes is if you have some physical disability limiting the amount of force you can apply to a petal with your leg.

My air dam is about 5 inches and some one else on here has an air dam on here made from a rock conveyer that is 3/4 inches off the ground, its a full size red truck and I cant remember the guys user name.
The lower part of my air dam is made from lawn edging and takes a beating but that's is by design. It is easy to replace.

[MetroMPG]

Originally Posted by Andrewhans

put the trans in neutral when coming up to stop signs and slowing down,

Just a note on this: are you familiar with DFCO (deceleration fuel cut-off)?

Depending on whether you're actually trying to slow down or whether you're just trying to coast, staying in gear is sometimes advantageous, depending on how your Tahoe handles it.

[Andrewhans]

Originally Posted by oil pan 4

I have seen plenty of 4L60E and 4L80E transmission vehicles be flat towed over the years.

My diesel also has hydro boosted brakes and I EOC and brake all the time.

My air dam is about 5 inches and some one else on here has an air dam on here made from a rock conveyer that is 3/4 inches off the ground, its a full size red truck and I cant remember the guys user name.
The lower part of my air dam is made from lawn edging and takes a beating but that's is by design. It is easy to replace.

That's good to know!

I won't be doing anything involving lawn edging as looks are still very important to me. I think I read about the red truck on this site. Pretty impressive actually. I don't want to scrape on everything which with my lowering kit happening soon I may have enough of a problem as is.

Originally Posted by MetroMPG

Just a note on this: are you familiar with DFCO (deceleration fuel cut-off)?

Depending on whether you're actually trying to slow down or whether you're just trying to coast, staying in gear is sometimes advantageous, depending on how your Tahoe handles it.

I would love to do this and I will be asking my tuner to add this to my ECU update. The Tahoe currently doesn't do it though.

[ChopStix]

The 2 things that helped me the most (thus far) have been narrow light weight tires with steel wheels. And having my stock computer programmed with the low altitude factory program.

Most aluminum wheels are actually heavier than stock steel wheels in the same size. And there was a recall on the stock computer for my van. The new program they put in made a giant difference.

My best thus far has been 26mpg highway. With my goal being 30mpg. My next mods will be new tires for summer, domed hub caps, electric fan conversion, and power pulleys. I wanna see where these leave me before messing with any aero mods. But a partial grill block, front and side skirts are in my future.

[Hersbird]

I'm surprised you are having that much trouble hitting 20. My sister-in-law had a 4wd 5.3 Suburban we borrowed and even towing a large popup camper with 7 passengers we got 15. Then in a all interstate trip not towing at 70-75 it got 18. Does your 17 include a lot of in town? If not I would think about trying w/o the chip for awhile.

[star_deceiver]

Hitting 18 on the interstate is fairly easy, so long as the wind is in your favour. I've only hit 20mpg once, that was from puttering around Yellowstone at 45 mph for several days. The aerodynamics at high speed is a wall that you won't overcome in stock form.

[Andrewhans]

Originally Posted by Hersbird

I'm surprised you are having that much trouble hitting 20. My sister-in-law had a 4wd 5.3 Suburban we borrowed and even towing a large popup camper with 7 passengers we got 15. Then in a all interstate trip not towing at 70-75 it got 18. Does your 17 include a lot of in town? If not I would think about trying w/o the chip for awhile.

I have the AWD model not a selectible 4wd system or even an Auto engage 4wd system. I am ALWAYS driving all 4 wheels. It does include a normal amount of city driving. All highway I was able to get 18.8 before my tune or aero mods. I haven't had a chance to run the same trip yet after the tune. The combined rating of 14 is pretty close to what I would expect most other people to get with my vehicle. I'm happy with anything over 17 on my day to day commute.

Originally Posted by star_deceiver

Hitting 18 on the interstate is fairly easy, so long as the wind is in your favour. I've only hit 20mpg once, that was from puttering around Yellowstone at 45 mph for several days. The aerodynamics at high speed is a wall that you won't overcome in stock form.

I think 20mpg on the interstae will be totally doable once I lower it 3 in the front and 5 in the back to bring the vehicle level and low. I will work on aero a little more with a bit of a belly pan to clean up the bottom some. But you're right there is only so much I can do before I hit an aero limit.