Poor Gas Mileage - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > Air Induction

Air Induction Performance Air Intake/Air Induction Modifications

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  #1  
Old 02-13-2010, 12:33 PM
Larf Larf is offline
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2007 Chevy TrailBlazer LT
Black 4.2L I6 4X4
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Poor Gas Mileage

Hi - I'm a newbie who recently bought an '07 Trailblazer, 4.2 engine, 40,000 miles. I found this site looking for info on gas mileage.

I'm getting 18 to 19 at 70mph, cruise control set, on relatively level highway. I'm comparing that to my brother's similar 2003 Envoy which gets 21 - 23 on highway.

Found lots of info on this site already - will start with the filter - believe I'll get a K&N. Then I'll clean the intake per instructions I've read here.

Everything else about the vehicle is Great.

I'll probably have more questions as I go along, and would appreciate any suggestions any of you have.
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Old 02-13-2010, 01:14 PM
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white06ls white06ls is offline
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thats not too bad actually, That is the same as I get in my 06 ls and many members on here have reported much worse fuel mileage on thier vehicles.

I would say your brother has diffrent gears than you have and that is why he gets petter fuel mileage.
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  #3  
Old 02-13-2010, 02:12 PM
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lynch55 lynch55 is offline
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I'd love to have that good of gas mileage!
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Old 02-13-2010, 02:37 PM
trailmezz trailmezz is offline
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2005 Chevy TrailBlazer LS
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I have an '05 and right now im getting about 15 mpg right now
I've replaced the air filter and changed the oil 3 times since buying it last year
i cant find out why its performing so poorly
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Old 02-13-2010, 02:46 PM
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lynch55 lynch55 is offline
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Welcome! That's about what I get and I've done everything except a PCM for less tune!
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Old 02-14-2010, 10:55 AM
mwfaith1971 mwfaith1971 is offline
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Quote:
Originally Posted by trailmezz View Post
I have an '05 and right now im getting about 15 mpg right now
I've replaced the air filter and changed the oil 3 times since buying it last year
i cant find out why its performing so poorly
What were you getting when the weather was warm. Also, are you calculating the mpg's by hand or relying on the DIC?

Matt
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Old 02-14-2010, 04:59 PM
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strat81 strat81 is offline
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Winter gas, ethanol blended fuels, cold temps, and low tire pressures conspire to destroy fuel economy. So can poor maintenance and aggressive driving. Run high quality synthetics in your differential(s), as well as the proper weight engine oil.

I'd run at least 35psi in your tires, assuming they're as good as the OEM tires (check your sidewall for max inflation). You can go higher if you're willing to tolerate a stiffer ride.

Not a huge fan of K&N filters as they can let a bit more dirt into the engine compared to a stock filter. Just MHO.
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Old 02-14-2010, 07:01 PM
Larf Larf is offline
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Thx for all the responses - I'll try to address all inputs.

We just got this vehicle after needing (wanting) a SUV, and liking my brother's so much. All cold weather here, and have only driven about 1500 miles , mixed highway and city. The highway stretch was about three 100 mile stretches, which isn't enough sample, but did cause me to wonder about the mileage. My vehicle doesn't have the instantaneous mileage feature like my truck, so I can't get a cross check. All info is from the DIC - I haven't yet confirmed its accuracy, which I will. I wanted to baseline before I change fluids, filters, etc. I'm checking by light driving on interstate, steady 70 MPH.

My reference is my brother's envoy (believe same gears as we both have 1900 RPM at 70mph). That gearing might be too tall for a gas engine in a two ton vehicle? Also, two Chevy trucks, both larger V-8's, and heavier vehicles, get better mileage than I "think" I am getting.

My plan is to change the air filter (I've ordered a dry Amsol), and clean the MAF inlet, change engine oil to synthetic (I use synthetic in all my vehicles). I'll also go to synthetic in gear boxes, which I believe is in there from the FActory - but I see that the change interval is at 50, 000 miles (I'm at 41000). Vehicle has new Firestone highway tires - at 40psi. And, I need to check the mileage , manually, on a long highway trip.

I believe these vehicles should get at least the 15 - 20 miles advertised. I've formed opinion, from my reading, that the vast majority of Trailvoys get at least the advertised mileage, but a small minority get less, for some reason - I want to find out if mine is in that category, why, and correct if possible.

One other personal data point - two two chevy trucks in our family experienced a dramatic reduction in fuel mileage at the 60 - 70K mile point - were well maintained, but we haven't found out why. They have K&N Filters, syn oil, but we didn't suspect a dirty MAF intake.

Even so, we are very happy with this trailblazer. Very comfortable, roomy, quiet, plenty of power.

I'll keep you all posted - let me know if you have suggestions.
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  #9  
Old 02-14-2010, 09:30 PM
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christo829 christo829 is offline
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Welcome!

If you've got a DIC, you can display the instantaneous or average mileage.
Check page 216 (I think) in your owner's manual, or just look for your
owner's manual here in the resources section.

Most immediate thing might be that throttle body. 40,000 miles is enough
to get cruddy. Don't just clean the front side.

http://forums.trailvoy.com/articles....ticle&artid=91

You might run some fuel injector cleaner through at the next fill up.

As was already mentioned, check tire inflation, and consider that *some*
of that lower mpg may be from winter blend fuel.

Good Luck!

Chris
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  #10  
Old 02-15-2010, 08:43 AM
mwfaith1971 mwfaith1971 is offline
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The DIC is a liar and usually shows higher than what you're actually getting.

Sounds like you both have 3.42 gears (the same as mine...I get 1900rpm @ 70mph) which are the best for highway use. 3.73 is probably the best for mixed city/highway and 4.10 will kill you on the highway but is best for just city work.

From my experience, V8's driven on the highway at a constant speed will get better mileage compared to a smaller engine, it's just less RPM's at the same speed.

Matt
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