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TERRIBLE gas mileage lately

38K views 167 replies 54 participants last post by  Super 88 
#1 ·
My trailblazer has been getting terrible gas mileage lately...i fill it up with premium, and when i fill up, it says about 185 miles to the tank, and it used to say around 240-250ish...

i just got my truck back from the dealership after getting an electrical problem fixed, and with 4/5ths of a tank, the DIC says i have 135 miles to empty

i feel like my mileage is alot lower than it should be, and i just installed a new K&N filter also.

when i reset the AVG MPG, i was going between stoping and about 35 mph, and within that time frame, the AVG gas mileage would not go above 10 or so...at idle, it would slowly tick down to as low as about 5...what gives??

My Oil life is about 47%, which may be some of the reason, and i plan on changing the oil soon...what oil do you reccomend?
 
#2 ·
My trailblazer has been getting terrible gas mileage lately...i fill it up with premium, and when i fill up, it says about 185 miles to the tank, and it used to say around 240-250ish...
I would say something is def wrong....as I too have a 03 LT....and after a regular fill up my DIC says 350+

When was the fuel filter changed last?

Any oil will work....but I believe everybody loves Mobil1 here
 
#5 ·
350+ to a tank? holy ****...i wish

how do you drive?? are you heavy on the pedal at all or do you take it easy 100% of the time.

I cant imagine what could be wrong...i bought the car december 15th 06....i havent personally changed the oil, or any filters except the air filter.

i thought the dealerships were supposed to change the oil for you? although my oil life was at about 74% when i got it
 
#4 ·
Mine is also that bad, but I have the 2" lift and 32" tires. Mine was alot better with the stock tune as well. The PCMforless tune is awesome in the power dept., but horrible for gas mileage (at least in my case).
 
#6 ·
My trailblazer has been getting terrible gas mileage lately...i fill it up with premium, and when i fill up, it says about 185 miles to the tank, and it used to say around 240-250ish...

i just got my truck back from the dealership after getting an electrical problem fixed, and with 4/5ths of a tank, the DIC says i have 135 miles to empty

i feel like my mileage is alot lower than it should be, and i just installed a new K&N filter also.

when i reset the AVG MPG, i was going between stoping and about 35 mph, and within that time frame, the AVG gas mileage would not go above 10 or so...at idle, it would slowly tick down to as low as about 5...what gives??

My Oil life is about 47%, which may be some of the reason, and i plan on changing the oil soon...what oil do you reccomend?
It sounds to me that your LTZ turned into an SS..LOL
 
#7 ·
My trailblazer has been getting terrible gas mileage lately...i fill it up with premium, and when i fill up, it says about 185 miles to the tank, and it used to say around 240-250ish...

i just got my truck back from the dealership after getting an electrical problem fixed, and with 4/5ths of a tank, the DIC says i have 135 miles to empty

i feel like my mileage is alot lower than it should be, and i just installed a new K&N filter also.

when i reset the AVG MPG, i was going between stoping and about 35 mph, and within that time frame, the AVG gas mileage would not go above 10 or so...at idle, it would slowly tick down to as low as about 5...what gives??

My Oil life is about 47%, which may be some of the reason, and i plan on changing the oil soon...what oil do you reccomend?
It sounds to me that your LT turned into an SS..LOL
 
#8 ·
Fill the tank and tell us how many miles till the light comes on. Then, fill the tank again and make a note how many gallons it took to fill up. Although the DIC is somewhat trustworthy you can't base anything scientific except for how many miles you get on the tank...not how much is remaining. In some places the gas stations have a winter "brew" with a touch more crap to keep water out of the tanks and can reduce mileage...being alcohol based or whatever.
 
#12 ·
first off, don't use the DIC to truly judge your MPG. They are not always right. Keep track of your miles and gallons and do it the old fashioned way.

Next, I would expect slightly worse mpg right now because of the temps and winter blend fuels. Nothing you can really do about it.

Next, I wouldn't trust the dealership to have done ANY of the proper maintenance. First thing I do when buying a used car is have all the fluids changed, everything lubed that can be, and belts and hoses checked. I have a mechanic check the brakes and the suspension. Better safe than sorry.

Next, if all that was done, I would think maybe you need to stop in and have it checked out. You should be getting better mpg than that. A PCM tune can help increase your mpg too.

I get over 400 miles to a tank too. I am tuned, and I have a bigger tank than you do.:raspberry
 
#16 ·
alright ghoster now why did you have to mention your mpg..400 is just crazy..im getting like 225 and i have a 04 ls..how do you manage 400??please share your knowledge..i got my used tb about a yr ago..should i do anything besides oil changes..u got me thinking now with all fluids and such..i got a fuel system cleaning which helped but still
 
#18 ·
alright ghoster now why did you have to mention your mpg..400 is just crazy..im getting like 225 and i have a 04 ls..how do you manage 400??please share your knowledge
Maybe he keeps 2 5 gal. tanks in the rear cargo for a quick fill


i bought my TB from a chevy dealer that has been around for years...

im talking to aerostud1026 on aim now and hes telling me the same thing about gas octanes..

maybe running mid grade would be more ideal for my truck??? or should i just go back to regular?
Go with what is in the manual unless you got a tune :D
 
#25 ·
I've been getting around 10-11 city ever since I got my 06. I'm gonna let it go for a while before going crazy about it though. It's only got 10,000 miles and I'm gonna let the weather improve and also wait to get in some mixed/highway driving in.
My gas mileage improved right up to about 15k miles. I don't want people to overlook ALL the facts about my mpg. I have a tune that give me a good mileage increase. I am required to run 91 octane because of my tune. I also have a CAI. My TB is an 04 LS 2wd, so it is lighter than most. I bought it new and put in Mobil 1 Synthetic at 300 miles. My TB has been meticulously maintained. The mileage I got was achieved driving from Virginia Beach to Miami and back. So I was at sea level or close to it the whole time, and it was late fall. The temps were cooler, but the gas wasn't a winter blend. I just want everyone to know that getting 20 mpg on the highway should be achievable for most Trailvoys.:cool:
 
#26 ·
My first highway trip resulted in a whopping 13 mpg over 200 miles. That was with the car LOADED with Christmas presents. My GF took it on a trip and with that highway driving mixed with some city driving I think it got like 14.5 or 15. This is an 06 TB LS 4x4. I plan on getting a tune in the coming months, so I'm not too worried about it yet.
 
#30 ·
Yea i notice alot of the time i have to give it a little extra gas then back off when it kicks in..waste of gas..tunes help alot in that department..you don't have to give as much gas to go the same speed
 
#31 · (Edited)
I was having bad gas mileage after buying my TB used as well. Usually getting 270kms to a 60L tank in the city and not much better on highway. Brought it in my shop this weekend and found/changed the following: After doing these things im at 300kms to this tank with about a 1/3 tank left

Changed fuel filter (115,000 kms)..it was so plugged I could barely blow thru it

While changing filter noticed a bad gas smell around the tank. After dropping my tank found the sending unit to be rusted very bad with pinholes in the supply and return line. This has been pumping gas all oven my tank and onto the ground....as it has been -30 here Ive only noticed a gas smell once or twice because im running from the house to the truck as fast as possible and going to full serve gas stations....so i fixed the sending unit!....take a smell under your truck by the tank, I think the design of the tank is going to cause a ton of these to leak

changed plugs

PCMforless tune installed
 
#33 ·
I forgot to mention the fuel filter on my 03 is at the front of the gas tank and is really easy to change, two lines and a bolt. About a 10 minute job when its in the air, just dont break the clips or have new ones on hand incase you do.....plugs are also very easy. I think without the sending unit problem it would have be an hour or so job for all three (plugs, filter, PCM)
 
#34 ·
dude47:

If you are getting 11 MPG like others said..then you have something wrong or an extremely heavy foot. The DIC will read between 2 MPG and 70 MPG or higher and average it all out. If you fill up and start driving around town then the DIC to read 10 MPG is normal, then on the highway it will start to come back up as it averages. What you need to do is take your TB to a good shop and hook it up to an exhaust gas analyzer to see if you are running rich while watching a scan tool. The ECM will compensate for a rich mixture so it is good to watch real-time values, If that checks out then you can troubleshoot elsewhere. If you have gone over everything and changed your filters and no vacuum lines are disconnected then I would have your exhaust sniffed...it's a good place to start.
 
#35 ·
Like all said. Lot of variables. Winter gas, tires need topped up when temp drops etc. Also when I had the dealer flash my computer One of the flashes was for a speedo calibration. Might check that. Plus use the odo and gal. to fill. I've checked almost every tank in my 04 2wd in the last yr. Lowest 16.0 highest 18.7 Use 87 octane also.

Of course I'm in Ks. pretty flat and straight here, just windy.
 
#37 ·
Interesting thread. I spent 10 years at GM helping GM dealers repair vehicles. My 2 cents on this subject is dirty oil will only make a marginal difference at best. Full synthetic motor oil will give you a small amount but nothing earth shattering. Synthetic oils advantage is that it doesn't break down over time like conventional mineral based. There are a lot of factors that influence mileage and some have already been mentioned here. My check list would start with the basics: Tire pressure, air and fuel filters, TB clean and verify no history codes in the ECM. This would be a good start. I have a 2002 1500 Silverado extended cab, 2wd with 3.42 axle, 5.3 V8 with a cap on the back. I can average a solid 20mpg cruising at 75mph. If I bring the speed down to 60-65(I know it's hard with today's drivers on the road) I have achieved a best of 22.8mpg. I am taking delivery of my 2WD SS this Monday so I haven't had a chance to play around with one yet. But, I did notice the sticker mileage is 15 city, 19 highway, which is the same as my Silverado was. OK, long enough. Good luck with it, post out anything you find.
 
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