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chevy trailblazer_ls
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3 Posts
Discussion Starter #1
Im so happy to finally get a trailblazer... Wanted one when they first came out... Well I have the bottom of the line but it saves me so much gas im happy.

I Love to mod cars so now to my 2 questions.

Question 1: Would gutting the airbox gain any MPG? I have read its restrictive. I havent opened it up yet. I could care less for horse power or performance changes, or sound. I have 2 very fast\loud cars already:)

I have read that the K/N setups and a few others change sound and some lost MPG afterwards. I also read the stock box is very restrictive and could be improved with a little dremel work.

Question 2: would dropping the CATs off gain any MPG. I have HPTuners pro and 6 credits left so I can tune out the rear O2s and adjust for A/F changes. However if it wont net me at least 2 MPG in doing any of this I would leave it as it is. It sorta looks like the pipes are plenty for the lil I6 but just curious.

Also I know weight reduction and a light foot will net the largest savings. Overall I am very happy with the truck.
Thanks in advance guys!!
 

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2002 gmc envoy_slt
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3,203 Posts
The factory airbox is restrictive and removing the inner liner of the portion that surrounds the filter itself will fix that. The stock tube isn't too bad though, but does have that acordian bend in it. Problem is that removing the intake restriction really only helps 3500 rpms and up, not where you're running if the mods are for fuel economy. (My Envoy cruises at 70 mphs at under 2000 rpms).

Removing the catalytic converter may actually hurt mileage. If you remove too much the back-pressure, the I6 sort of falls flat on its face below 2500-3000 rpms. Members who have replaced both the muffler and resonator with a single very low restriction muffler (or used 3" piping) have reported detrimental affects on mileage. - Adding a glasspack or anything to put just a tad restriciton back in usually fixes it. (Our motors actually like some restriction in the exhaust). That may stem from the very restrictive exhaust ports in the head, who knows. (Lots of metal there that could be removed or ported out).

Best two bang for the bucks mileage wise are a TUNE and E-FANS. In over 10 years of ownership, I've tried them all. I have a Borla exhaust, installed a CAI w/K&N Filter, Airaid spacer, you name it....the ONLY two things that made any noticeable change in fuel economy were the tune and e-fans. The exhaust *might* have helped a tiny bit, .25-.33 mpg, the intake made no apparent difference, the tune gained me 1-2 mpg and the e-fans another 1-2 mpg, depending upon speed and driving style.

If your mileage is extremely low, as in WELL under 20 on the highway or 14 in town, also check your CPAS (cam phaser solenoid) and upstream O2 sensor. When they stop working properly, they can make a profound difference in fuel economy. The I6 is a great motor, but seems to be finicky when it comes to mods.
 

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chevy trailblazer_ls
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Discussion Starter #3 (Edited)
Thanks,

I couldnt have asked for a better answer. I may research the electric fans. I saw a thread about using the C6 fan setup. There has to be a cheaper alternative with good cooling. Does anyone know what is done on the economy tune other than dialing in the MAF and VE tables?
 

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2002 gmc envoy_slt
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Hate to break it to you, but an '02 doesn't have use a MAF, we use a MAP sensor combined with an IAT (Intake Air Temperature) sensor. The volume of air flowing into the engine is calculated using those readings, along with throttle position and rpm. The GMT360 platform didn't switch over to a MAF setup until I believe '06...might have been '05, but pretty sure it was '06.
 

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2002 gmc envoy_slt_xl
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Following...

Has this thread died flat on it's track?
I just had my Voy (02 XLSLT 4x4) and I only get Inst/Ave MPG 13.0-13.ish.
Anything that will help with the MPG is where I am at... I am loving this rig! I should've bought this long time ago. I bought this "resistor" thingy... that you install on the IAT sensor... have yet to find out if it's really gunna give me at least 3MPG and 5-10Horses.:undecided
 

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2005 chevy trailblazer_lt
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137 Posts
I get better mileage now than I did six yrs ago with 100k less miles. This is proven to help ME

Drive slower off a start

Keep it under 2k rpm. Do it. Yeah you're going slow but you want mpgs not 0-60right?

Keep tires psi in check.

Drive slower when merging

Eliminate startup run time. 30secs and go- SLOW

I have a K&N drop in filter. Not sure what this resistor thingy is you speak of but sounds like
Tunes have been proven to help. But some report faster accerlartiob and by doing so compromise the mpg tune.
Drive Slower.
I actually do 5-10mph under the limit-stop light stretch etc- roll rt through. Takes patience but I've gained some over the years.
Did I mention Drive slower and coast more? Double your coast time to stops and stay under the speed limit ( I dare ya)

There are some other over the top miss you can do. I got 24+mpg driving east through South Dakota doing about 55mph the whole way. Yeah it sucked but I was on the road all day anyways and just shows what speed does to you mpgs. If I ever get over 2k rpm Im going to the torque max at ~3600rpm or 5k to blow the cobwebs out. Low rolling resistance tires; Michelin, Generals, etc are proven. Avoid the all terrains. My $2.
 

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2002 gmc envoy_slt_xl
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I get better mileage now than I did six yrs ago with 100k less miles. This is proven to help ME

Drive slower off a start

Keep it under 2k rpm. Do it. Yeah you're going slow but you want mpgs not 0-60right?

Keep tires psi in check.

Drive slower when merging

Eliminate startup run time. 30secs and go- SLOW

I have a K&N drop in filter. Not sure what this resistor thingy is you speak of but sounds like
Tunes have been proven to help. But some report faster accerlartiob and by doing so compromise the mpg tune.
Drive Slower.
I actually do 5-10mph under the limit-stop light stretch etc- roll rt through. Takes patience but I've gained some over the years.
Did I mention Drive slower and coast more? Double your coast time to stops and stay under the speed limit ( I dare ya)

There are some other over the top miss you can do. I got 24+mpg driving east through South Dakota doing about 55mph the whole way. Yeah it sucked but I was on the road all day anyways and just shows what speed does to you mpgs. If I ever get over 2k rpm Im going to the torque max at ~3600rpm or 5k to blow the cobwebs out. Low rolling resistance tires; Michelin, Generals, etc are proven. Avoid the all terrains. My $2.
I couldn't agree more with you on those points...
And there's no way I could even go for a fast get way off a stop here in our place... too much idiotic drivers (esp. when it is raining). Not that I race or whatnot with this big of a rig. I have a passenger of (always) 5 with me when I drive my Voy so I am after mpg.
 

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2008 chevy trailblazer_lt
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12 Posts
I get better mileage now than I did six yrs ago with 100k less miles. This is proven to help ME

Drive slower off a start

Keep it under 2k rpm. Do it. Yeah you're going slow but you want mpgs not 0-60right?

Keep tires psi in check.

Drive slower when merging

Eliminate startup run time. 30secs and go- SLOW

I have a K&N drop in filter. Not sure what this resistor thingy is you speak of but sounds like
Tunes have been proven to help. But some report faster accerlartiob and by doing so compromise the mpg tune.
Drive Slower.
I actually do 5-10mph under the limit-stop light stretch etc- roll rt through. Takes patience but I've gained some over the years.
Did I mention Drive slower and coast more? Double your coast time to stops and stay under the speed limit ( I dare ya)

There are some other over the top miss you can do. I got 24+mpg driving east through South Dakota doing about 55mph the whole way. Yeah it sucked but I was on the road all day anyways and just shows what speed does to you mpgs. If I ever get over 2k rpm Im going to the torque max at ~3600rpm or 5k to blow the cobwebs out. Low rolling resistance tires; Michelin, Generals, etc are proven. Avoid the all terrains. My $2.

+1

24 mpg is really good, I'm going to shoot for that. Best I'm getting is about 20mpg right following most of these tips. Driving style is 90% of good mpg. Sensor issues reducing mpg or mods to add mpg only help a little.
 

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2005 chevy trailblazer_lt
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137 Posts
Don't get me wrong, I usually get 18-19mpg on highway depending on speed and traffic, 20-22 if I keep it under 65mph and 2k rpms. The time through SD getting 24 was really a test of patience and max mpgs. I probably won't do it again to save the $10-20 over 400some miles. Driving all day heading west in the winter I often see the same car(s) pass me several times a day. I stop less for fuel and the extra stops do not save me any considerable time to make it worth my while. Last trip I took solo, there were two vehicles that blew by me earlier the previous evening I saw parked at the rest stop catching their Zzz's in the morning that were not there when I arrived. one even was idling with the windows down:weird:
 

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2007 gmc envoy_denali
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If you have a red light in front of you slow down before you get to it and hope it changes to green before you get to it. In town it saves a lot of gas, just touching that accelerator drives the MPG down quite a bit. I can squeeze out 15-16 in town. The wife gets 12-14 because she don't watch her foot.

On the highway I usually get my speed up to around 75 or so going down hill and try to coast up the hills best I can. I have gotten 22-24 mpg on the highway. Cruise control drinks the fuel unless your on a straight flat road for a long time.
 

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2002 chevy trailblazer_ls
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i installed a K&N CAI a month ago and have noticed an increase in gas mileage of 2mpg better and the overall perfomance is better as well.the engine also runs alot smooother.havent set off the check engine not one time.good investment as far as im concerned
 
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