H3 gas mileage SUCKS

[sharkman]

I am trying to find out what the average MPG you are receiving on your H3. I have 5500 miles on the truck and have received AN AVERAGE of 14-15 mpg driving on the freeway. I have taken the truck to (2) dealers and neither can find anything wrong with the vehicle. As they say, "the vehicle is performing within specified parameters." Is anybody else experienceing the crappy gas mileage?

[sharkman]

I am trying to find out what the average MPG you are receiving on your H3. I have 5500 miles on the truck and have received AN AVERAGE of 14-15 mpg driving on the freeway. I have taken the truck to (2) dealers and neither can find anything wrong with the vehicle. As they say, "the vehicle is performing within specified parameters." Is anybody else experienceing the crappy gas mileage?

[FormerJeeper]

I'm getting between 17.5 and 19.1 MPG.
Mostly freeway driving.

-C

[sharkman]

Have you done anything to your vehicle? What speeds do you drive?

I added a K&N filter and a flowmaster exhaust (both are supposed to improve the gas mileage). Also, I have the roof marker lamps, a brush card w/ PIAA lights attached and the luggage rack.

[MxHonda]

K&N filter, Mobil 1 Oil, 3,000 miles, 18mpg city/hgwy AC on all the time... How heavy is your foot?

[f5fstop]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by sharkman:
Have you done anything to your vehicle? What speeds do you drive?

I added a K&N filter and a flowmaster exhaust (both are supposed to improve the gas mileage). Also, I have the roof marker lamps, a brush card w/ PIAA lights attached and the luggage rack. </div></BLOCKQUOTE>

Marker lamps MIGHT cut down on some fuel economy since it is a wind restriction, but not that much.
Here is a thread I submitted last week on my fuel mileage I recorded on a trip. Vehicle had less than 1K when I left, and had only about 2200 when I returned. I expect it to go up as the engine breaks it, maximizing around 4-5K on the odometer.
The only speed limit I know is one where I drive safely, not what is posted. Average speed was around 73 mph per my GPS, but I hit 85 a few times, and I-65 through KY is not flat, especially when coming out of Louisville.
TN, believe it or not, is downhill out of KY, but still some rolling hills. Also some traffic through the larger cities.
As for the filter; K&N makes a lot of statements, and I never checked fuel mileage with one, but I can tell you from dyno'ing a Vette (and a few other Vettes on the same day owned by other people), K&N's statement about increased HP is BS.
As for exhaust, there is not that much restriction in the newer mufflers, and if all you did was setup to the rear of the resonator and the cat, you will not see much in the way of fuel economy over a stock muffler, and no increase in HP.
In the olden days, when mufflers were more restrictive, I would say a cat-back was a good investment. Now, it is more for looks and sound; and there is nothing wrong with that.
Good luck, and I sure hope you get your mileage figured out by a dealer.

[bparker]

Please take note, when you make changes to airflow - such as an intake or free flowing exhaust - you MUST - give the vehichle at least 500 miles to adjust the air/fuel mixtue to optimize results. As if you make a judgement before this it will be based off of a rich or lean condition.

[sharkman]

Good question. I drive about 75-80mph, give or take with the AC off. HUMMER claims I am driving too fast and this vehicle isn't meant for those kinds of speeds. How fast do you drive, typically?

I don't accelerate abruptly, either.

[sharkman]

I appreciate the input. I have put almost 4000 miles on the truck since the modifications.

[sharkman]

what mpg did you get on this trip, average?

[H3OH]

LOL! This is a funny thread. http://www.elcova.com/infopop/emoticons/icon_rolleyes.gif

Gas mileage is great for me. It's better than what my friends are getting with their SUV's.

As someone else mentioned, how heavy is your foot? Are you stomping it at the light? Manual or auto? Driving habits? Need more specifics to see what your "problem" is.

[sharkman]

My foot isn't heavy at all. I do tend to drive 75-80 on the freeway (which is what Hummer says is the problem). I traded in my YUKON XL for this truck and I haven't changed my driving habits at all. Ironically, the Yukon, with a 5.2L V8 got better gas mileage than this H3, with the 3.5L inline 5. I definitely don't accelerate at a light or stop signs. My H3 is an automatic.

[MyxH3]

Well I for one have a heavy foot and I have been averaging around 14-16 in the city and between 17-19 on the freeway,I average 75mph and have an automatic. I drive 50 miles each way to work and its a combination of city and highway. I am loving it I get alot better mileage than I did with my Xterra. Although that said i havent driven it loaded down yet but that is coming at the end of the month.

[f5fstop]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by bparker:
Please take note, when you make changes to airflow - such as an intake or free flowing exhaust - you MUST - give the vehichle at least 500 miles to adjust the air/fuel mixtue to optimize results. As if you make a judgement before this it will be based off of a rich or lean condition. </div></BLOCKQUOTE>

Air/fuel misture on the modern engines is almost instantaneous. The PCM constantly reads the O2 sensors, as well as the MAF sensor, air temp sensor, ect., it then computes the most optimum air/fuel ratio, and constantly changes this as you drive. Chaning the air filter or cat back exhaust will be sensed almost instantly by the computer. Besides, there is litte to no affect with these items in regard to air/fuel mixture.
The transmission has a learning capability, called adaptive strategy, that will adjust with driving over a period of time, usually within 50 miles.

Sharkman...
Explain to the dealer that many states have speed limits of 75 mph, and the vehicle is more than capable of driving at that speed. If some idiot at the dealer says the vehicle is not designed to drive the speed limits in many states, then they have to purchase the vehicle back. The vehicle is only governed by the speed rating on the tires. It won't even come close to redline at the governor speed.

jkH1+H2=H3
The off-road tires on the H3, which I have are not going to affect fuel mileage that much, if at all. The PCM is programmed for the larger tires. I would agree if I replaced my tires with 35 inch Mudders, but not with the stock off-road tires.

[jkH1+H2=H3]

Wow, you guys travel fast!!! Im getting at least 17mpg to 19mpg. I travel the highest @ 70mpg. One more speeding ticket, I go to Jail!!
Also, What tires are you Running. With the 33's, I was told that will drop down the MPG.
Logically speaking, its like riding a mountain bike vs. a Road Bike. A road bike will give you more mpg at a higher rate of speed. With MTB Tires on a Road is about 9 to 12 mpg. Road tires will Be @ 15 MPG up to as fast as you can pedal 24-30 MPG.
Also, Remember, the V5 engine is not a hole shot type of engine if your in motocross, OK, Slow, slow,, in the get go,
allow the engine to build speeed....
If you are Gunning it all the time, to go faster, everytime you gun it, Ching, ching, ching, glug, glug, glug, you want me to give you speed, give me your gas!!!!!!!!!!!!!!!

[mightypuck]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">sharkman
Hummer Novice
Posted 09-13-05 05:00 PM
Good question. I drive about 75-80mph, give or take with the AC off. HUMMER claims I am driving too fast and this vehicle isn't meant for those kinds of speeds. How fast do you drive, typically? </div></BLOCKQUOTE>
75-80mph...you have to drive that fast here in California or else you're going to get rear ended...by a semi, yep those damn 18 wheelers http://www.elcova.com/infopop/emoticons/icon_biggrin.gif

[killian]

I'm not real sure that I care what kind of mileage I'm getting, I just enjoy driving my truck.

[bparker]

Yes, those are the short term fuel trims and they are changed for driving conditions - but they will not be correct until the long term fuel trim tables are updated after 500 miles - then and only then will the short term fuel trim tables be accurate and optimized.

Brent

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by f5fstop:
Air/fuel misture on the modern engines is almost instantaneous. The PCM constantly reads the O2 sensors, as well as the MAF sensor, air temp sensor, ect., it then computes the most optimum air/fuel ratio, and constantly changes this as you drive. Chaning the air filter or cat back exhaust will be sensed almost instantly by the computer. Besides, there is litte to no affect with these items in regard to air/fuel mixture.
The transmission has a learning capability, called adaptive strategy, that will adjust with driving over a period of time, usually within 50 miles. </div></BLOCKQUOTE>

[sharkman]

I drive exactly like you (45 miles each way to work) and a combo of city and freeway. The BEST MPG I have gotten is 14-15. That is why I am so frustrated: the H3 is supposed to get close to 19 and I am not anywhere near that. I keep telling Hummer there is an issue with this truck, but nobody seems to care.

[Sharkster]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by killian:
I'm not real sure that I care what kind of mileage I'm getting, I just enjoy driving my truck. </div></BLOCKQUOTE>Same here too. I would only notice the mpg if it was at an extreme... (like e.g. in an H2), but otherwise I don't care. I had a Mercedes ML 320 before I got my H3 and I think it was subjectively at the same mpg consumption... but I never researched the mpg "in-depth". http://www.elcova.com/infopop/emoticons/icon_wink.gif

[wannabeH3]

i really enjoy the H3 but i fully agree the mileage is pathetic and no where near the advertised 20 mpg i typically get between 13-15 mpg

[f5fstop]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by bparker:
Yes, those are the short term fuel trims and they are changed for driving conditions - but they will not be correct until the long term fuel trim tables are updated after 500 miles - then and only then will the short term fuel trim tables be accurate and optimized.

Brent

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by f5fstop:
Air/fuel misture on the modern engines is almost instantaneous. The PCM constantly reads the O2 sensors, as well as the MAF sensor, air temp sensor, ect., it then computes the most optimum air/fuel ratio, and constantly changes this as you drive. Chaning the air filter or cat back exhaust will be sensed almost instantly by the computer. Besides, there is litte to no affect with these items in regard to air/fuel mixture.
The transmission has a learning capability, called adaptive strategy, that will adjust with driving over a period of time, usually within 50 miles. </div></BLOCKQUOTE> </div></BLOCKQUOTE>

In short (no pun intended) the STFT is a PCM erasable memory register and has direct results on fuel mileage during closed loop operation. The PCM changes the injector pulses per this information.
The LTFT is a matrix arranged by the PCM and MAP, and as the engine operating conditions change over time the LTFT is changed within the PCM.
Your PCM on the H3 will try its best to keep a air/fuel misture of 14.7:1, while the engine is in closed loop operation, no matter what the LTFT tables are showing as compared to the STFT.
Basically the LTFT is used primarily for engine warm up and WOT conditions; primarily open loop operation, and the O2 sensors are not warm enough to signal, and the coolant is still not at operating temp as signaled by the coolant sensor. STFT is the instantaneous correction value determined from the O2 sensor readings (after they have warmed and started their signals to the PCM and the coolant is at operating temp) and is functional during closed loop operation.

If you are trying to obtain fuel mileage during warm up and WOT operations, then I would agree LTFT is important. However, for driving as explained and normally performed by most drivers, STFT is what is important.

In addition, as I said before, the K&N statements are very overrated, and have little effect on air/fuel mixture in real life.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by sharkman:
I drive exactly like you (45 miles each way to work) and a combo of city and freeway. The BEST MPG I have gotten is 14-15. That is why I am so frustrated: the H3 is supposed to get close to 19 and I am not anywhere near that. I keep telling Hummer there is an issue with this truck, but nobody seems to care. </div></BLOCKQUOTE>
This thread started out with you saying you were driving on the freeway, which I took as constant speed. Now you say it is a combo of city and freeway. City/highway is not advertised as 19 mpg; that is a measurement of highway only and is figured as all other vehicles during ideal conditions at a set speed. (Not saying this is right, but it is the way the Feds want fuel mileage figured...at this time.)
My total city mileage appears to be coming in at around 14.5 MPG; 1.5 MPG less than per the ratings, but I am well known for jack rabbit starts, and I hit almost every traffic light on my 11 mile commute each way; so I can't really complain.

[oneworld]

alomost 2000 miles and the truck is averaging about 15 > 17 > most of my driving is 70 to 80 on the highway and around town softer not working the brakes hard at every stop >so I guess I am not pushing the gas around town. It takes a bit to stop the momentum of the wieght on the H3 so my local driving is low key not ziping around town.

[HummerNewbie]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by f5fstop:
but I am well known for jack rabbit starts, </div></BLOCKQUOTE>

My dog thinks I do that as well http://www.elcova.com/infopop/emoticons/icon_biggrin.gif

[trading13]

LOL thats cute. I hope a saint bernard fits ok in an h3.

[Desert Dan]

for a 4700 pound brick shaped SUV I think the mileage people are reporting is pretty good!!!

I wish my Jeep did as well.

GM didn't claim 19-20 mpg in the city!

[DWPC]

Driving a 4700 pound 4WD brick with a big pipe rack and lights bolted to the front at 80 MPH and complaining about mileage takes chutzpah. I don't know of any vehicle that doesn't take a major mileage hit at speeds over 70 vs. EPA figures, which we all know are optimistic anyway.

The H3 ain't nevergonna be a SoCal freeway cruiser (unless it gets a diesel), but I bet if you cut your speed to 65-70, you'd see a large mileage improvement.

I don't mean to be a wise-a##, but buying an H3 to commute 90 miles a day!! What were you thinking?

[sharkman]

I appreciate your candidness. The reason I am complaining is that the new TrailBlazer SS has a 395HP LS2 engine (the same as the new Corvette). The Blazer weighs the same as the H3 AND it is rated with the same gas mileage (16/19). I asked HUMMER and Chevrolet how this can be possible: how 2 similar weighing vehicles (outside of aerodynamics) can have 2 totally different engines (a V8 vs an inline 5) and get the same gas milegae! Hell, if I know about the SS, I may have purchased it over the H3 (you get power AND great gas mileage). The answer given to me was, "I know it is frustrating, but I don't know how to explain it."

[H3OH]

Makes you wonder why there are new Trailblazers just piling up at used car places such as Carmax. Do a search on their site and you'll see plenty of 2005 Trailblazers up there. It's scary.

[DWPC]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">How 2 similar weighing vehicles (outside of aerodynamics) can have 2 totally different engines (a V8 vs an inline 5) and get the same gas milegae! </div></BLOCKQUOTE>

It IS the aerodynamics! Drag goes up with a cube factor. The H3 is a box (actually a bunch of boxes stuck together). Compared to the H3, the TB is downright streamlined. Going from 70 to 80 increases your H3's already high drag dramatically.

[jp's-h3]

Could altitide affect mpg?
I live in slc,ut. and get pretty good mpg (16-17 city)
I'm not sure what I'm getting for hwy mpg. will have to check soon. I LOVE MY H3!

[ChevyHighPerformance]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by f5fstop:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by bparker:
Yes, those are the short term fuel trims and they are changed for driving conditions - but they will not be correct until the long term fuel trim tables are updated after 500 miles - then and only then will the short term fuel trim tables be accurate and optimized.

Brent

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by f5fstop:
Air/fuel misture on the modern engines is almost instantaneous. The PCM constantly reads the O2 sensors, as well as the MAF sensor, air temp sensor, ect., it then computes the most optimum air/fuel ratio, and constantly changes this as you drive. Chaning the air filter or cat back exhaust will be sensed almost instantly by the computer. Besides, there is litte to no affect with these items in regard to air/fuel mixture.
The transmission has a learning capability, called adaptive strategy, that will adjust with driving over a period of time, usually within 50 miles. </div></BLOCKQUOTE> </div></BLOCKQUOTE>

In short (no pun intended) the STFT is a PCM erasable memory register and has direct results on fuel mileage during closed loop operation. The PCM changes the injector pulses per this information.
The LTFT is a matrix arranged by the PCM and MAP, and as the engine operating conditions change over time the LTFT is changed within the PCM.
Your PCM on the H3 will try its best to keep a air/fuel misture of 14.7:1, while the engine is in closed loop operation, no matter what the LTFT tables are showing as compared to the STFT.
Basically the LTFT is used primarily for engine warm up and WOT conditions; primarily open loop operation, and the O2 sensors are not warm enough to signal, and the coolant is still not at operating temp as signaled by the coolant sensor. STFT is the instantaneous correction value determined from the O2 sensor readings (after they have warmed and started their signals to the PCM and the coolant is at operating temp) and is functional during closed loop operation.

If you are trying to obtain fuel mileage during warm up and WOT operations, then I would agree LTFT is important. However, for driving as explained and normally performed by most drivers, STFT is what is important.

In addition, as I said before, the K&N statements are very overrated, and have little effect on air/fuel mixture in real life.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by sharkman:
I drive exactly like you (45 miles each way to work) and a combo of city and freeway. The BEST MPG I have gotten is 14-15. That is why I am so frustrated: the H3 is supposed to get close to 19 and I am not anywhere near that. I keep telling Hummer there is an issue with this truck, but nobody seems to care. </div></BLOCKQUOTE>
This thread started out with you saying you were driving on the freeway, which I took as constant speed. Now you say it is a combo of city and freeway. City/highway is not advertised as 19 mpg; that is a measurement of highway only and is figured as all other vehicles during ideal conditions at a set speed. (Not saying this is right, but it is the way the Feds want fuel mileage figured...at this time.)
My total city mileage appears to be coming in at around 14.5 MPG; 1.5 MPG less than per the ratings, but I am well known for jack rabbit starts, and I hit almost every traffic light on my 11 mile commute each way; so I can't really complain. </div></BLOCKQUOTE>

In part throttle while the engnie is warm, the PCM reads the pre-cat O2 and adjusts the injector pulse width to maintain ~14.7:1 A/F. The PCM uses Strims and Ltrims together to adjust the A/F during part throttle. Strims react fast and Ltrims are slowly adjusted to bring the Strims hovering about zero. The PCM adjusts very quickly during part throttle. The issue is when you go to WOT. During WOT the PCM enters power enrichment (open loop). The PCM zeros the Strims and uses the data learned in the last cell (before entering WOT) as a calibration for WOT. No learning is done during WOT. So if you don't give the PCM enough time to learn the Ltrims for the cells, you can have undesired WOT performance. If you understand the cell arrangement, learning can be done in about 10 - 15 miles. Otherwise you may need 50 - 100 miles to be sure the "used" cells have learned.

This is an issue with dyno testing immediately having made a modification. If you look at WhiteH3's dyno from K&N, you'll see that only 3 miles were added beteeen the stock air box and K&N's. This is too short for a learning process and with a better breathing air box (like the K&N) results in a temporary lean WOT running which is shown on the A/F plot (11.13 stock and 11.92 with the K&N). (After the PCM has learned, the WOT A/F with the K&N will return to the 11.13.) My guess is that this test was also run with the hood up which helps prevent the K&N intake from drawing in hot underhood temperatures.

[f5fstop]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by sharkman:
I appreciate your candidness. The reason I am complaining is that the new TrailBlazer SS has a 395HP LS2 engine (the same as the new Corvette). The Blazer weighs the same as the H3 AND it is rated with the same gas mileage (16/19). I asked HUMMER and Chevrolet how this can be possible: how 2 similar weighing vehicles (outside of aerodynamics) can have 2 totally different engines (a V8 vs an inline 5) and get the same gas milegae! Hell, if I know about the SS, I may have purchased it over the H3 (you get power AND great gas mileage). The answer given to me was, "I know it is frustrating, but I don't know how to explain it." </div></BLOCKQUOTE>

it takes less throttle input to move a vehicle with a large V8 with torque to spare, versus a five cylinder that does not have torque to spare. Yes, a V8 with less throttle input is using more fuel than the five cylinder using the same throttle input, but the five cylinder would require a great throttle opening. This would only affect starts from a stop, unless you were passing.
Also, even though the trailblazer is not considered aerodynamic, it is extremely aerodynamic when compared to the Hummer H3, which is similar to moving a wall down the road.
I'm also guessing, but I would guess the trailblazer weighs in at about 500 pounds or less than the H3. The H3 has a heavier frame, extra cross members, and heavier front/rear axles and transfer case.
As I have said earlier, the fuel mileage figures given are based upon a Fed Regulation on how to determine fuel mileage. These tests are performed under ideal condition, and really do not reflect actual driving done by you or me.
It does sound like you not getting as good of mileage as others, but it could be due to your driving habits versus others, the wind, the altitude, etc.
I know from what I have seen so far with my mileage, I have no complaints.

[sharkman]

Thanks for the input. I am going to drive 2 full tanks @ no faster than 70mph highway and see what happens to my mileage.

[bparker]

Have you checked to see if you have any Hondas or Toyotas stuck under your bumpers? You might have one adding weight to your vehice thus poorer milage. /shrug

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by sharkman:
Thanks for the input. I am going to drive 2 full tanks @ no faster than 70mph highway and see what happens to my mileage. </div></BLOCKQUOTE>