I wouldn't go spending a bunch of money on mods with the sole intention of increasing mpg's. I bought a 2006 Adv. pkg H3 this year w/38k in excellent condition(looking back it actually had bad tires, a bad rear shock, old paper air filter and most likely out of alignment) and i got 16 mpg. i mostly drive highway 55-70mph. I fixed all of the above and still got 16! drives alot nicer though. So i bought a volant Cai, got a nice hp increase but no mpg increase. then i got a magnaflow cat back system, looks and sounds good but IMO not much hp and again 0 mpg increase.
The ONE thing i did that increased my gas mileage was changing my differential fluid using royal purple and changing my transfer case fluid. now i get 16 -16.8 mpg. (i have a gas app on my iphone) haha

So if you want the H3 to be a little quicker get an intake. the dual exhaust looks and sounds good but imo neither increases mileage.
Hope my long winded story helps some. good luck

 

Easiest is harder tires....I am running 38 right now. Harder than this should increase mileage a bit more but the road ruts get very noticeable.

 

Here's my setup that i've had for 3 years on my 2006 H3:
PCM4less board
K&N CAI
Corsa Catback Dual exhaust
MickeyThompson MTZs 35's
1-2 miles gained, maybe. I'm sure if I had the stock tires I probably get more, but then again I end up pressing the pedal harder! LOL! I'm gauging about 12/city 14/hwy... filling your tires to 50psi helps as well.

 

I am not trying to sound like an A$$Hole but if you where concerned about mpg's. You should not of bought a Hummer. I have an 06 Titan V8 that gets better mpg's than my H3. I'm just sayin'!

Cheers
-Deryl

 

As I said in my first thread I knew what I was getting into buying a hummer. I don't expect great mileage at all but I wouldn't pass up the opportunity for a few extra mpg. Thanks to everyone else for the useful positive input. I'm gonna go with a cai and the PCM once I get my mods done. Thanks guys

 

Hey sorry, I sit next to a guy that bought an H2 and all I hear all day is how bad gas mileage he gets. It's annoying. I hope you get your mods and what not and they work out for you.

-Deryl

 

partly pride,its a classy,UNIQUE ride,a friend says,"feel like miletary!"
face it h2,3 is fun,enjoyable to drive, feels safe,so mileage is average.
i quit that focus on mileage and focus on resource allocation. i just put more budget in the h3 tank and less elsewhere,,like my gut. i could double mileage in ???, then what?, spend the saving on some junk!

my focus gets to be good wax jobs AND underside paint,protection,rust prevention, maintain value,appearance for me and the next guy.

and #1,,,drive every day for pure enjoyment,,,gotta gooo

tom

 

I bought a K&n Cold air intake not to long ago and found it does improve Gas mileage i have also installed dual exhuast 3 chamber flow master. i have a 2006 H3 Adv 5spd manual i have 285/75/16 Dick Cepek Mud Country tires. Changing your diff and transfer case oil will make a difference in gas mileage. i do alot driving and average 17-17.5 mpg i dont really know if the 5 spd manual is what makes the difference.
if you cant get a big improvement in gas mileage just drive the hell out of it and enjoy it. congrats on owning one and good luck .



Fred

 

Just my story, not saying it's the norm.

PCM tune, gas mileage dropped with what I truly believe was the same driving habits. Dealer, without asking, updated the PCM and mileage went back to normal.

I added a Volant CAI. No increase in mileage.
I added the GM dual touring exhaust. No increase in mileage. It's louder though, which is cool I guess.

I've pretty much given up. I bought my H3 because it fit me, not for mileage. But to touch on what some others have posted, it just makes sense to get the most out of what you have.

For me, it seems it doesn't matter what I do, I still get about 14 city. Keep in mind that I drive 95% city. It sucks but from home-work/work-home, it's 25 miles round trip of zig-zag, stop sign, stop light city streets. That could be a factor.

 

Not to get off topic, but, did you contact PCMforless? Were they willing to help you out with a re-flash, or were you just out the $200?