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Hi, as I'm sitting here writing this, infront of autozone after the standard oil change and top offs (if needed), and purchased a bottle of high mil. Seafoam. I, the code reader, the tech, are In complete confusion as to why my 2008 Chevrolet Malibu LT 2.4L. Is giving me such awful MPG. I purchased this about 2 years ago, from an authorized dealship at exactly. 84,320 miles, no visible damage, passed smog, serviced when I'm supposed to. The only thing I've had happen to me, 1) Had to replace starter (caught on fire), 2) new battery, 3) New ACDelco spark plugs, 4) New tires(6 months ago) all 4, all balanced and what not, and of course the typical driverside headlamp, but wasn't the headlamp but the way it was wired(common from reading). My next purchase will be the brakes, but from what the dealership told me they were around 65 - 70% wear, and there was no visible scratches or drag. I live in the armpit of CA, temperatures reach no less then 60 degrees in winter, but up to 107 in the summer.
So now the problem. Besides the TPMS constantly on even though I've always made sure, (because any kind of bump or sound in the road my GF thinks her tires are flat but, no they're not.) My DIC reads and has dropped from when we first bought the car. Roughly 25mpg(just an estimate), to 17mpg(not enough for me to freak out). But now it's down to 13.3MPG. We don't drive anywhere but in town, we've put less then 50,000 miles on it, it doesn't have any issues starting up or accelerating. I've been using premium gas after reading through the forums, I just don't understand anymore. Please, any insight 馃檹. As to what's next, please let me know. Everything that was replaced, was replaced with the original part listed from manufacturer. If you guys need anything else from me, let me know. As I said before, the code reader shows no codes, the techs said no visible leaks, and its not rough idling. Just gets costly filling it up every other day. Thank you.

-Rich.
 

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2011 Malibu LTZ 3.6L V6 Red Jewel Tintcoat
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Get the codes read, and use a scanner that can dig deep, like the BlueDriver or similar. You may also need to start looking at the fuel trims and other live data, so having a scanner capable of showing you that info is almost a necessity with today's cars.
 

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2017 SS Sedan 6.2L
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We always have to ask this, so don't take it personally:

1. Have you confirmed the DIC fuel economy readout with your own calculations of miles driven divided by gallons to fill up?

2. Are you excessively using remote start (if your Malibu is equipped with it)?

3. Is the car exhibiting any other odd behavior when driving (poor acceleration, engine noise, etc)?

The TPMS notice just means the sensors need to be replaced, that's normal.
 

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2008 Malibu 2.4L, LT, FWD, 117k (1/16/22)
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@romeenvy : I can tell you my son drives this exact same vehicle up in New England, and even now somewhere north of 100k miles (still waiting for his update), he鈥檚 getting over 30 mpg.

As has been mentioned above, I would first try resetting the DIC鈥檚 fuel economy reading, then filling up, resetting the trip odometer, driving through that tank, and seeing what I got. If that was still as low as you say, then I鈥檇 be hooking up my Harbor Freight code reader with 鈥淒ata Logging鈥 to capture the Fuel Trims. Maybe you have a bad O2 sensor that is telling the ECM to leave the injectors open longer (running it 鈥淩ich鈥, and wasting fuel). You might also find an issue with your MAF sensor, which is mis-reporting the amount of air coming into the combustion chamber.

The computer uses inputs from the engine sensors to control devices which operate the vehicle. If they鈥檙e totally dead, it can tell you that, but if they鈥檙e mis-reporting (because they鈥檙e failing, or because some other device or element is confusing them), it鈥檚 software may not be smart enough to detect that, and it may just assume the input is 鈥渃orrect鈥, and react to it.

UPDATE: 117,631 (1/16/22)
 
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