Bad Gas Mileage on my newly acquired trailblazer

[Rgorman11709]

I would like like to start by saying thank you for letting me join this site. I have been an avid jeep owner for the last 10 years so I am very new to these vehicles. My last jeep was a 2000 grand cherokee with a 4.7L V8. I averaged 14 miles per gallon. Considering the upgraded tires and performance mods I figured this was in the norm. I have gone through 2 tanks on my 2005 trailblazer. And have averaged 13 miles per gallon. I have a 30 mile highway round trip commute to work 5 days a week. I figured I would be doing a little better than that. Not sure how many options there are on these but it's a 2005 trailblazer LS. It has 121,000 miles and had been mechanically maintained buy the original owner since she bought it new in 2005. It does have a 2hi option and that is what I use. I figured it might be because of the remote start and how long I was letting it run for. But I stopped using it for a week to see if there was a difference and there really wasn't. I'm going to do new plugs and wires this week and see what happens. I'm not sure what I should be expecting out of this for had mileage but 13 just seems really low for. Straight 6 with factory tires and no lift. Any advice would help. Thank you.

[navigator]

welcome Ryan, I did a search for bad gas mileage and found several links.
This link might have some information for you.
viewtopic.php?f=26&t=4874&hilit=bad+gas+mileage
You might try a similar search and browse through some threads.

[DustinC1989]

Welcome

I run the largest tires possible with no modifications and average 21mpg

We have some links on here about this issue, read around and hopefully you can find something that helps

[Cable810]

Welcome!! I average 17mpg 32s, 3" lift and 4.10s

[Wahugg]

Are you going off the DIC or calculating it by hand? The DIC tends to be wrong all the time. According to my DIC I am only getting 14 MPG, calculation by hand yields 18mpg.

I'm 3" lifted with 32" tires 3.73 gearing.

-Wahugg

[The Roadie]

Deferred maintenance can be a problem. Use Delco 41-103 plugs only. Change every ounce of every fluid in there, especially the transfer case, which needs it every 50K religiously. 100K for the diffs and coolant. Air filter, etc. We have some discussions on our non-offroading platform-specific sister site gmtnation.com for traditional 100K maintenance and gas mileage improvement projects. If you discovered our old clubhouse hangout trailvoy.com in your Googling, forget them. They're dead except as a reference library.

[Cable810]

Are you going off the DIC or calculating it by hand? The DIC tends to be wrong all the time. According to my DIC I am only getting 14 MPG, calculation by hand yields 18mpg.

I'm 3" lifted with 32" tires 3.73 gearing.

-Wahugg

Its all by hand. I use Mikes formula He posted to figure out my actual miles and I go from there.

EDIT:Your probably talking to the OP and not me.....

[Rgorman11709]

Yeah I'm calculating this my self. I'm getting about 220 miles a tank (filled up at 17.45 gallons). Comes out to roughly 12.6 mpg. This is the second tank now and not any better. I'm definitely going to purchase the oem ac delco plugs and wires along with change all the fluids and air filter. I'm also going to pull apart the throttle body and clean it out along with putting a fuel treatment and fuel filter other than those things. I'm at a loss. Hopefully Ill see a decent improvement after these things. I'll let you all know. Thank you.

[The Roadie]

Don't trust any parts store that tries to sell you plug wires.

[HARDTRAILZ]

Welcome.


Definitely avoid the wires.

[navigator]

have the o2 sensors and Tstat been replaced?
If your temp needle doesn't point directly straight up to 210 that is good indication you need a new Tstat.
Make sure you read up on replacing the Tstat as it is more involved than most other platforms.

[DirtyBacon04]

120k miles and I'm willing to bet the throttle body has never been cleaned. While i dont see it causing a 8mpg drop, it is still sucking some out for ya. There's several DIY threads for cleaning our throttle body.

here's one i made
http://forums.offroadtb.com/viewtopic.php?f=32&t=4520

[Wahugg]

If I were in your shoes I would do these items in this order to alleviate your problems.
-Throttle body cleaning (probably will not do much)
-Spark Plug replacement (original AC delco Only)
-Upstream O2 sensor replacement (original AC delco Only)

Now these may not have to do with your gas mileage problem but they are important to do if they haven't been done yet.
-Tranny pan drop, filter change, and top off
-Differential fluid change front and back
-Transfer case fluid change ( THIS ONE IS VERY IMPORTANT. Only use the original GM fluid).

Best of luck
-Wahugg

[DirtyBacon04]

Original GM fluid for xfer case being AutoTracII

There are no aftermarket substitutes.

[mikekey]

I'm curious, what upgraded tires you have, what performance mods you have and what gear ratio you have, unless the tires and performance mods were in relation to your Jeep, but it sounded like you meant the Trailblazer.

If you're running around on 35's with 3.42's well then, duh. If not, then follow the advice above.

[Rgorman11709]

Good call on the wires. Hahaha. I haven't even had time to pop the hood or even research what I'm working with. I ordered the oem ac delco plug. It's a 2005 so It doesn't have a serviceable fuel filter. Ordered a volant cold air intake. I'm going to clean out the throttle body when I install the intake. I'm also chasing a new check engine light. The light will come on for about 10 miles or less every 4 days. I'm sure this has a lot to do with it but whenever I try and run somewhere to get it scanned it turns off. I have been less than a mike away from an auto parts store and it shuts of twice now. I'm honestly about to buy a scan took so I can scan it when it shows up again. Thanks again for the help

[jonbo2002]

I had the random check engine light and one of my coils were bad, might be you issue with millage too but wait till you change your plugs and see if that is the problem first.

[Diacom]

Welcome, not much to add that hasn't already been covered above. Hope those work for you.