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bad fuel mileage!

35K views 34 replies 23 participants last post by  DrivenDaily 
#1 · (Edited)
I have a 09 LTZ with L4 and 6 speed. It has 16k miles on it. 27mpg is the best it has ever gotten. I have driven fast and driven it slow. I drive 50 miles one way to work every day. All 4-lane or interstate. Just wondering if anyone else is getting bad mileage and what you have done to fix it. The dealership told me they haven't heard of any mileage problems, but they will reflash the ECM and see if that will fix it.
 
#2 · (Edited)
There are a lot of variables that account for your MPG, what kind of highway/interstate is it you drive in? Hills, mostly flat, or steep mountain type roads?

I tried to see how high I could get my MPG on a road trip from LV to OR, 33 was the highest I got it. That was driving at the speed limit and drafting behind other vehicles helped out too. I made sure to have my tires properly inflated and had just changed the oil too.

That was the first and last time I'll do that, your 27 seems to be a more realistic number though.
 
#4 ·
I'm down from 34-35 to 31 in mixed (2/3 of my driving on interstate and beltway, average speed @ ~40 miles/hour combined). I suppose A/C takes a toll. My MPGs are actual (as opposed to the DIC) from miles driven vs. gallons used. I drive alone, with not much cargo, ~10 lbs of emergency stuff in the trunk. I suppose 27 isn't far-fetched given the heavier LTZ.
 
#5 ·
When I've used the method that Richard suggests, that of resetting the DIC's Avg MPG just as I get onto the freeway, I've actually been able to get it up to 36.1, and I've got the V6!

A couple of months ago I was returning with my sister from Elizabethtown to Louisville on I-65 North. The speed limit is 70 for most of it but I was doing 60. We had gone 70 on the southward leg but wanted to see how much that extra 10 mph did to the mileage. There aren't any mountains on that part of the road but there are a lot of rolling hills and a few steep passes, but no large elevation changes (probably 100-400 feet each). Most of the way it was registering around 34-35. When I got closer to town and the limit dropped to 55 it started to go up again. Once I got off the freeway and hit surface streets it started to plummet, but that's to be expected.

I used cruise control all the way, tapping off only when traffic required it. And the AC was on.
 
#7 · (Edited)
I just thought it would have gotten better. We had an 03 Accord before this, and it averaged 30-32 with the same driving. I think the 6 speed hurts it more than anything. Any type of incline and it has to downshift all the way to 4th to catch up.
I'll agree in principle that the A6 is not a performer. I can force it into a gear more easily by using the tap shifters than I can by using the ol' press-and-release of the skinny pedal.

Mine doesn't go to 4th when it downshifts to regain lost speed up a hill. One way I know that is after it shifts, sometimes I'll pull it into "M" and it says 5th. I was curious because it sounds like it's up-shifting twice once it gets back to the preset speed. I'm sure others who feel like commenting will assure you that first it shifts up from 5th to 6th gear and then it locks the torque convertor. TCC lock is what feels like the second shifting of a gear, making you (and me at the time) think it had down-shifted to 4th and then had to up-shift twice to get back to 6th.

See if your air filter is excessively dirty, ensure that you're using the correct grade of gas (for V6 GM recommends 87 or 89), and that your fuel system is not compromised by dirt or deposits. Most of the time I use top-tier gasolines, and occassionally I fill with mom-and-pop gas, but that's rare. I always use 89. I no longer waste my money on 92 and don't want the reduced performance of 87.

Another thing to consider is that I took off my huge muffler that is overly restrictive and put in its place a Y-pipe and dual resonators, along with the original factory dual tips. Sounds better, but regarding this thread, it might also be giving me an improved exhaust flow through lower restriction, enabling the slightly higher MPG numbers. Or not. But it isn't hindering it any, of that I'm sure.
 
#8 · (Edited)
I hate to say it... but have you considered slowing down?

My commute is 99% highway and I'm averaging 25MPG with the 3.6. That's running 75-80 the whole time and kicking down to pass at will. My mileage goes up to 27 or 28 if I just stay in one lane and do 65-70.

Just cruising on the highway you should be able to get 30MPG no problem out of that 2.4.

The 6-speed is wonderful in these cars. Not only does it enable the 3.6 to really scoot, but it keeps the 2.4 in the heart of the power band, making the most of the available170hp.

You also have to consider that this car weighs more than your Accord. The 2003 Accord tips the scales at ~3300lbs. The 2009 Malibu LTZ is ~3600... 300lbs difference. That's like carrying around a football player.

What octane are you running? I know the manual says it will do fine with 87, but the 2.4 prefers premium. I go by the old muscle-car saying, if compression is over 10.0:1, use premium.

Finally... how hard are you accelerating? To get the most out of the 2.4 you have to keep the revs pretty high, above 4000 where the cam timing kicks over, if you are running the engine at above 4000RPM a lot then your mileage will also suffer. One of the reasons I went for the V6. I can get performance out of it adequate to keep up with traffic without going above 3000RPM.
 
#9 ·
My 2011 Malibu has only gotten 19 mpg average. I am so frustrated with the car that I am beginning to hate it! I asked the dealer about it and they said they couldn't do anything about it! It doesn't matter whether I go local or highway, fast or slow! Does anybody know what I can do? Thanks.
 
#20 ·
I also have a Malibu 2011 2LT with the 4cyl. and get crummy gas mileage, although I burn E-85 which is supposed to give you less mileage. I've gotten as good as 24mpg on a mixture. I do mostly town driving which also probably screws up the mileage. My car is now in the shop for a leaking tranny and they screwed up when cleaning my fuel system and expanded the fuel tank, due to a faulty valve in the fuel system. Thank God I'm covered under my warranty, so I have a loaner, also a Malibu, 2012 LT. I don't know what I'm getting on that as yet. My car has been in the shop for over a week though. I was a previous Honda owner and I'm beginning to wonder if I made a good choice.
 
#10 ·
Average over how many miles? I have an '11 V6 and my lifetime average across 29,000 miles is 19.707. I usually get around 18-20 in town and can get 25-30 on highway.

How are you determining your mileage - by the DIC or after filling up and doing the math? The DIC should be fairly accurate, but if you never reset it you'll get lifetime average (possibly covering only 1000-2000 miles, not sure). Resetting it after each tank will yield tank averages.
 
#11 ·
I also have a 4 cyl with the six speed in my '10. Had it for almost 3 years. I can never get anything higher than 26 based on the readout which imo sucks. With every other vehicle I have ever owned I always get very close to the stated mileage on the Marony label. This is the first vehicle where I get considerably less. My '12 Grand Cherokee with the 290 hp six gets about 23 as a comparison.

Since my warranty will expire next month I plan on taking it in to see if there are any flashes that could help.
 
#12 · (Edited)
19 mpg is quite low, however, since 99% of us are getting much better mileage, there must be something wrong, the car, or the driver. i have been doing a lot more city driving in the past 2 weeks and i have been pushing it a bit, much more aggressive than before. My mpg went from 29.5 to 27.6 according to DIC. Mind you, i got the 4 cyl.
To be honest with you, I have always beaten the sticker epa on all my cars, but one: the 1500Ram (what a bitch that was). Hell, I got 39.8mpg out of the boo, but i admit, that was no fun :)
 
#13 · (Edited)
It is probably important to ask what type of driving the driver is utilizing, what are the environmental conditions, and is he/she using the DIC avg? This also goes to everyone else.

The average combined is 26 by the EPA. It's 22 city and 33 hwy. 19, depending on where the vehicle is in it's life isn't far off the 22 mark. If it's a new engine and it's mostly city, you're going to see low figures, but it'll come up when the engine opens up. Likewise, getting anywhere near 30 is going to be accomplished on the highway cruising at 60+ mph ... not in the city or any sort of stop/go situation.

Edit: Missed the 50 miles on interstate. In that case, yes that's bad, but here's a question ... is the 19 you're seeing by resetting the DIC as you enter the interstate or is 19 what your average on the DIC is stating, which is taking everything else into account.

For the record, I drive 25 miles each way on interstate (50 miles+ a day) and my DIC avg is 24.5 ... but this is because of traffic and then the city on each end kills the near-30-mpg.

Also note, if your foot is constantly on and off the gas pedal ... that will kill your gas milage no matter where you are.
 
#14 · (Edited)
My 2012 with the 2.4L just hit 4000 miles and mileage has went up a bit. The computer is saying average 34.5 mpg after I reset it for the week, which is the highest numbers yet. I always top off the tank til the fuel is at the top of the gas filler and then do the math after every fill up...my last tank doing the math was 33.5 mpg, mostly highway miles on mostly level road at 60mph. My lowest mpg has been 26 mpg in alot of stop and go traffic with hills combined with some highway....but the computer was saying the average was 28 mpg....so I really think the computer is just a guide and not the actual mpg the car is getting.
 
#15 ·
My '09 2.4 w/84k miles has gone up on the DIC from 25.3 to 27.1 over the 5k miles I've had / been driving it. 2 drivers BTW. No highway trips yet either.
Several Seafoam treatments, synth. oil and a K & N seem to have made the difference in my car.
This was a Co. car so I know it never had any fuel system maint. and probably was not on a top tier fuel diet or synth. oil either.
Just been using the DIC for reference as my wife uses the car on rainy days and may not always fill it up or record anything since it's the "beater" car in the household.
Car had a cheapo quickie lube air filter in it when I got it but it was clean so I left it in for a while, I think that was a big contributor to the what I think was a low mgg for a 4 banger. Her Mustang runs 22 mpg on it's DIC in the same use BTW so 25 mpg from a motor half the size seemed poor IMO.
More miles will be the proof positive......
 
#17 ·
I don’t think the computer is just a guide. It’s measuring the exact volume of fuel going into the combustion chamber and the actual mileage the vehicle is moving to calculate the mpg.
It’s also important, like someone already mentioned here, to reset your DIC every time you fill up to get an accurate reading of mpg for that tank, otherwise your averaging the mpg over all the tanks of fuel burned.
I have the four with the 6 speed, and my best Highway, long distance drive, was 36.6 mpg. I drive round trip everyday 94 miles, mostly two lane highway with lots of traffic lights in some areas, and I get 30.5 to 31 mpg in the summer and 32 +mpg in the winter. It has a lot to do with driving habits, at least for me, when I’m careful I get the mpg I just mentioned, when I drive without thinking about it or fast acceleration or last second breaking it drops off 4 to 5 mpg.

Anyway, just my thoughts and experience.
 
#19 ·
The DIC fuel economy readout has been discussed on these forums pretty frequently. While the measurement may be based on fuel injector readings, there is still a certain amount of error (which will decrease over the next decade or so) and as a result, pros like the people at Motor Trend and Car & Driver calculate their own fuel economy rather than rely on the digital display.

My car is always optimistic by .5 to 1 mpg. For some people, that's close enough, but I'm pretty particular about such things.
 
#18 ·
Cold weather starts, and the idling your car does when warming up and how it drives for those first few minutes also hinder your mileage. I went from almost 400 Miles on a tank average to 225-250 miles on a tank, because of the -30 degree temps in Alaska. Although I assume you are not experiencing this extreme right now, it could be one of the issues.
 
#21 ·
I just drove 503.5 miles on 14.600 gallons in my V6. I left at 9:40 AM, filled up at 5:55 PM, and maintained a cruise control set speed of 60. I didn't do any tricks going down hills like turning off the key, but I did put it in neutral (engine running!) to coast and pick up speed for free.

Doing the math that's 34.486 mpg on a V6!! If I can do that at 60 the I4 should be able to get pretty dang close or even surpass that while doing 70.
 
#23 ·
I have a 2012 1LT 2.4l. On my last 250 mile trip my DIC read 32.8, my Average Speed on the DIC was 63. While on the highway, I had cruise set at 69. This was all Minnesota driving, flat, no appreciable wind. For whatever it is worth, the OnStar MyLink app on my phone says my lifetime MPG is 24, I have 5600 miles now. My guess is the miles are 60-40% split city-highway.

I can't get better than about 20-21 in town, but my highway mileage is almost always between 31-33. I do notice, I can easily make both of those drop an MPG or two if I elevate my driving style from conservative to spirited for any length of time at all. In town, I try to keep the RPM's under 2500.
 
#25 ·
Currently on a road trip with the Malibu... figured out through the use of my ScanGauge that if you lock it in 6th gear in manual mode, you can hold it to the floor from about 55 mph to 70 mph and still make 26 to 28 mpg. The engine is at a low enough speed that it won't inject any more fuel than that. By using manual mode and losing a few mph on the hills and not down shifting unless really necessary I managed 28 mpg on one tank and yesterday got 34 mpg on a tank. I took a pic of the DIC showing a fuel range of 597 miles when I filled up!

Overall average is just over 26 mpg and we've been making anywhere from 20 to 25 mpg in town. This is the first longer road trip we've had it on.
 
#28 ·
On top of that, I've never been able to top off as much as 0.4 gallon no matter what pump I've used. It's usually something more like 0.1 gallon or less. So even though the example above was just an example to make a point.

Even with different pumps and topping off one time and not another, the manual method will be able to yield more repeatable results than a computer that uses laboratory averages for mass-produced items. The injectors are good but they don't all meter the exact same amount of fuel. Instead the computer allows the emissions to fall within a range that's allowable instead of chasing an elusive "perfect 10" goal. So, by assuming that the system is injecting "X" amount of fuel when in actuality it's injecting a different amount, even if off by only a very small percentage, what it assumes is constant and will never correct itself over many tanks like the manual method does just by virtue of the fact that you can't pump 17 gallons into a 16-gallon tank.
 
#31 ·
I can, but I have to be working on the car in the driveway when it's cold out and running the engine to keep the heater going (and the battery charged ... don't ask me how I know!), and it was really low.

But yeah, 12.9 MPG means something really bad, or is that display set to metric units and you weren't aware of it?
 
#32 ·
Techron and keep the tires at 35/36 psi help a lot. This weekend was a 1900 mile trip to IA and back. Worst was 27mpg and best was 31mpg. This was with me not being gentle and "keeping up with traffic".

Try using the manual mode - it helped me quite a bit on the freeway holding on in 6th gear.
 
#33 ·
Most common issue for bad mpg without a CEL on is brakes dragging. Frozen caliper pins or stuck calipers most common item.
 
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