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gas milage is poor

9K views 18 replies 7 participants last post by  campb292 
#1 ·
Hello I have a 09 lt with 2.4l 6speed trans. I have owned since new the car has 112k on it now.

my issue:
I have noticed that the average gas mileage has decreased from 23-25 down to 19-20. Has anyone else had this issue? the car seems to still run fine. I don't drive as often now. I have turned it over to my daughter to drive.

other information that may be useful:
At a 100k sparkplugs were changed and the cam position sensor had to be replaced. last year I noticed the same issue but found that the original brake pads had delaminated on the rear. That improved the gas back up to about 21mpg average. I put a bottle of seafoam in the tank annually.


Over all this has been a good car. yes the actuators started getting flacky about 3 years ago but the rest has been smooth sailing.

thanks

beerman
 
#2 ·
What I have experienced on my '09 now at 185k miles is that caliper pins like to stick causing brake drag. Cleaning the MAF sensor can help mileage, unless you have a high end scan tool you can't really tell if it's going out of range. My sensor finally died at around 180k miles. Cold weather and warming up the car and winter mix fuels will pull down mileage also. Warming up the car is zero MPG. I use injector cleaner at every oil change and only top tier fuels. BTW I'm the mechanic on my vehicles for everything. Driving habits could be a factor also, she may have a heavier foot.
 
#3 ·
the brake fluid was flushed when we replaced the original pads at 100K about a year ago. I did not notice any drag after that or now when I drive. I can clean maf it might help. my daughter does like to let the car warm up in the morning it might have something to do with it. If it was my son driving the car than I would be looking at how it was driven.
 
#4 ·
Kids can definitely be the cause of fuel economy drop. Not just from lead foot aggressive driving, but also from young driver habits, hard braking, not using cruise control, going 15 over the speed limit, doesn't take much to lose 3-4 mpg. Warming up the car for extended periods can drop 2 mpg by itself.

Could also be something mechanical like an O2 sensor on the brink or the cat getting clogged. MAF, engine air filter, and throttle body should all be examined when you have time.
 
#5 ·
Just curious but how are you keeping track of your mileage? If you're using the car's message display i'll tell you that i've found my 2010's to be fairly inaccurate, I keep track with an app on my phone and it almost never shows what my car tells me. In fact my car can vary greatly from one tank to another with consistent driving habits but my full tracker app will show a consistent MPG from one week to another.

Also when you said you replaced the spark plugs what did you use? OEM is Iridium plugs, if you used copper or even platinum plugs they could be wearing out more quickly than the factory plugs did and could have an effect on your mileage. Also every now and then it doesn't hurt to look at some other maintenance items like cleaning the MAF, running some injector cleaner through it, and i'm always uncertain if these cars have a fuel filter or not but if it does that certainly should be something you'd need to change.
 
#6 ·
Just curious but how are you keeping track of your mileage? If you're using the car's message display i'll tell you that i've found my 2010's to be fairly inaccurate, I keep track with an app on my phone and it almost never shows what my car tells me. In fact my car can vary greatly from one tank to another with consistent driving habits but my full tracker app will show a consistent MPG from one week to another.
Is this something that is similar to just taking how many miles you went and dividing it by the amount of gallons you put in? That's what I always did and found that if you fill up more frequently, that your amount will be much higher than what it really is. I remember mentioning this myself. Maybe @DrivenDaily can shine more light on it as he explained the situation to me at one time since I said that I could get as high as say 33MPG and my car would only say around 24-25MPG.
 
#8 ·
When filling up and getting only 1/4 or 1/2 a tank, an extra ½-gallon squeezed in after the last click will make a bigger difference than if you fill up with 3/4 to 7/8 of a tank.

If your tank holds 20 gallons (not ours, just for easy math) and you get 1/2 a tank, you'll click off at 10 gallons. Add another and you've just changed that to 11.

If you click off at 15 gallons and another, it becomes 16.

So now let's say that you usually get 30 MPG, which means that you should have driven about 300 miles on the 10-gallon fill and 450 on the 15-gallon fill. 300/10=30 and 450/15=30, so all is right with the world. But add that extra gallon and now it's 300/11=27.3 MPG and 450/16=28.1 MPG.

The smaller the sample size (10 gals. vs 15 gals.), the larger the percentage that the extra gallon will make when using it to calculate your MPG. "But wait, there's more!" It evens out over time.

I have a spreadsheet that keeps my fill-ups along with the per-tank MPG and the lifetime MPG. If you use an extra gallon after driving 50,ooo miles, it won't affect the MPG compared to only 300 miles.

My DIC routinely is optimistic by about 1.5 MPG each tank. Once you know your car, you'll be able to more accurately estimate your MPG as you drive, and then when you calculate it manually, or use a spreadsheet to do the same thing, you should be able to get pretty close to real life.
 
#9 ·
I do know the car. we have put all the miles on it. I used to rest the trip every fill up to calculate the mileage and compare it to what the computer said they were with in 1 mpg. I know fill ups can very. the variance I am at 3 mpg twice your 1`.5 and it has been consistant.
 
#10 ·
update. I found that the exhaust manifold was cracked the gas was down to 18.4 mpg. I changed the manifold and have driven the car about 200 miles the average is now 22mpg. I also noticed that the 02 sensor was in bad shape the little holie cover over the sensor is all but gone.it is the original. I have not changed it because I did n't want to have several variables. I will check the mileage this weekend. I plan to order a new sensor and will change it when it comes in and see if it helps.
Also the car has never used oil since new. that was until I checked it when doing the other work. I had to add 3/4 of a quart. the car seems to run fine good actually. I hope this is not an indication of something else going wrong.

I did not know the manifold cracking was such an issue on these engines. It would be helpful to the community if there was a list of common problem on this car. IE the cam position sensor, manifold, door lock, and other things I have not had pop up.
 
#12 ·
Thank you for updating us on your mileage issues, it's always very helpful to post your resolutions and changes to the situation. I think your idea for a master list of common issues is pretty good, and long overdue. When we (mods/admin) have time after the holidays we'll have a huddle and try to put something together.
 
#13 ·
A great example of a O2 sensor getting lazy but not bad enough to be out of range and trigger a code. Thanks for the update. I ran my 09 to 190k with the cracked manifold, mileage still in the mid twenties, OEM sensor , car still on the road with a different owner now. Belonging to this group educated me on the manifold, door lock issues, fretting corrosion, etc. issues allowing me to be more proactive in keeping my ''beater'' running for those miles.
 
#14 ·
O2 sensor question : getting the right one may be more difficult than I thought. looking at rock auto it lists different sensor for 4 speed and six speed trans, different for LTZ, LT. different for V 6 or 4L. when I cross reference the part # for Denso and AC it says the part does not fit my car. so can someone give me the correct PN for up stream O2 sensor on my LT 2.4L 6speed transmission.

AC 213-4299
or
Denso 2344673
 
#15 ·
2134299 AC is the correct upstream sensor for a 6 speed 2.4 per Rock Auto. They are my go to parts information site.
 
#16 ·
I ordered the denso before you posted. I use denso a lot on my Toyotas with good results. I checked denso site and it listed my car model as correct. On Amazon it said it did not fit my car but on the actual part it lists Malibu with 2.4 for my year. You cant always count on their information.

I will also state you can't always take rock auto as the final word. I got brake rotors for my Porsche and they were totally wrong. I had to prove it to rock auto with picks showing difference to get them to pay for shipping.
 
#17 ·
Porsche is it's own animal itself, I would be cross referencing every where. Amazon is out in left field. OEM may be Denso, I just put plugs in my '15 'bu and the coils where marked Denso in it.
 
#18 ·
update. replaced the o2 sensor. it does not seem to have changed the fuel efficiency. still around 22 mpg around town. I did drive it on the interstate about 20miles to a friends house and watched the estimated mileage. on flat road I am able to cruze at 60 and get 34mpg again. I pulled all plugs and cleaned them. I still don't understand why the car lost burned 3/4 qt of oil. it does not seem to have burned any in the last 400 miles. all seems good so this will be last post unless something changes
 
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