Gas milage help!!!

[adamw89_2000]

Ok, I know I didn't buy my hummer for fuel milage but I'm averaging 7.5 by my dic panel! Yea and I'm pretty sure it's accurate as much time as I spend at the pump... It's an 05 sut lifted 8" with 40" mud Trappists and 20x12 fuel rims. The tires are 15" wide as well. I have the cats removed which is throwing a code at the moment and I have stock gearing in it.... Is there anything I can do to this thing to get better than I am now? I'm starting to drive more and if I pussy foot it and go very slow I get almost 9... This is all in town milage for the most part. Any suggestions?

[TGCOFTN]

WOW, I could drive mine at 80-85mph and the absoulte "WORST" I have ever gotten is 13mpg. Both of mine are 100% Factory/Stock with the exception of lots of Chrome.

[Lucky1]

7.5 mpg sounds pretty normal with your set up to me. I'm stock height with 325/50/22's (35") and my computer says 10.7 and sometimes lower. I had a major tune up recently and it ran a little smoother but the gas mileage was still about the same. It has to do with aerodynamics which H2's have absolutely none ! If you own a Hummer then you have to pay to play.

[Hellz]

your running 40 inch tires!!!!

be glad you are getting 7.5mpg.

you can regear to help increase your MPG.

you can do the little mods like new spark plugs, wires, and fluids..

im running 37 inch tires and average about 8.9MPG on the DIC.

[SMITH23H2SUT]

Have you tried throwing it in neutral and coasting down every hill you come to.

[Lucky1]

Hellz is right, 7.5 mpg is not too bad for 40's with an 8" jack. Also I don't think any Hummer I've ever owned has gotten 13 mpg, not even brand new ! Lol...

[adamw89_2000]

That's not very exciting news. Lol o know rehearing may help on highway but I'm not sp sure here in town cause I'm turnin so little rpms. I will due a tune up since it is prob due but you think the code for the cats not being there is hurting it any? Maybe makin it run richer or something? Yea and these dudes r literally like driving a Brick wall down the road. Me and wind r not friends!

[HummerJim]

With the lift and the tires, that sounds pretty normal on mileage. I haven't reset the mpg on my stock H2 since I bought it new and it's stayed on either 11.1 or 11.2 mpg for the last three years.

[Indy]

Tires and windresistance will seriously lower your mpg...How much pressure are you running in the tires?

[glennf1]

Your cats removed are actually helping your mileage a little bit. You gain a little more up top but loose a little low end torque.

[adamw89_2000]

hmmm, ok wekk does not sound like much will help me then... im running my tires at 40 psi ..

[HUMTECH]

If you have no cats and your setting o2 sensor codes it will run in base fuel all the time, open loop operation. Thats whats killing your mileage.

[HUMTECH]

Larger tires will hurt mileage in stop and go traffic as it requires more throttle input to get going but will increase highway mileage as it has a taller gear ratio. Fix the "No converter problem" then see how it goes from there.

[Cesardajr]

Are you running a tuner/programmer to help recalibrate the gear ratio for the new tire size?
If not that will help, just make sure you find a tuner that can tune for the 40" tires.

[adamw89_2000]

Should I just get high flow cats or should I try and get some of those 02 sensor simulator things?? Ian not running a tuner at the moment.. U think that will help? Who makes one capable programming for a tire that big? I've though about gettin s custom time done rather than a hand held but not sure which would b better overall now.

[HUMTECH]

Simulators work good, have them on my 98 truck. If they are available for the 6l def would. If they are not available you need some cats. Ive never sourced them for a 6l so i honestly cant make that call. Google is your friend...

[tyler1bo]

Wouldn't a regear help? Like 4.88's?

[DeLH2]

I'm getting 13 on the highway and 10 in the city with lift and 37" tires. Wonder why yours is so low?

[LoJac963]

from what I read real quick the LQ4 is pretty identical to the LS2. I know when I had my GTO there were quite a few guys running O2 sims without any issues what so ever. Give the sims a shot and see if the MPG changed.

[glennf1]

Originally Posted by HUMTECH

If you have no cats and your setting o2 sensor codes it will run in base fuel all the time, open loop operation. Thats whats killing your mileage.

The o2's upstream *before* the cats effect fuel trim. The o2's *after* the cats have no effect on fuel trim and are only there to make sure the cats are working for emmissions.