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Discussion Starter · #1 ·
Get 320 miles per a tank. Used to get close to 400.

2014 eco with 74k miles.
Fac plugs gapped to .030
Pcv fix with intake
No codes
70mph on highway gives me 23mpg
93 or 91 octane used. Tried diff stations.
Normal driving , barely into boost..
Tb and map sensor cleaned
Scanner shows..
No codes
Engine temp is 191 f


How do I know if I have a bad O2?
 

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I would think that a bad O2 sensor would throw a code, but I haven't had that happen on mine yet.
Tire pressure (or lack therof) killed mine on a tank or two. Basic stuff like a dirty air filter can drop your mileage as well, but I suspect that you're good on both of those.
 

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Thats some sucky miles there. I been getting 31~35 mpg avg with readings around 40 hwy. I live in the hilly part of new jersey & do alot of city driving. But my motor also has 250,000 miles. So I tolerate my mileage. Tank only holds 11.5 gal so I do better than most.
 

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It's winter time.
Air filter
Tire pressure
Time to change the oil? MIne drops at 4k. And drops even more at 5k. From 36 to 28.
 

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O2 sensor can definitely cause a drop in mileage before it gets bad enough to throw a code. Change it between 50 -75k miles. The downstream one doesn't matter for fuel economy, that one is just measuring how well the catalytic converter is doing. The upstream one however directly effects fuel trims.
 

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Discussion Starter · #6 ·
Tires are 35 psi cold.
Amzoil oil and wix filters every 10k. Uses no oil
Air filter has about 25k on it.

I will buy a new 02. You guys know the part number? Is it an account delco?
 

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In my region temps are in the teens.

My economy is down by 6 mpg right now with 10k miles on the car. The place I filled up at seems to have dropped in quality from when I first bought my Cruze 16 months ago. But 6 is pretty low even for them.
 

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Cold weather will drop mileage b/c of denser air to push through, different winter blends of fuel makes it easier to start but worse mileage once its warmed up, thicker grease / oil, etc.

However, 23mpg @ 70mph warmed up on an ECO is way low even for cold weather.

my 2014 ECO 6MT gets realistically 37-42MPG summer with LRR summer tires and 32-35MPG winter with heavy Snow tires.
 

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I read this in a auto repair trade magazine. As O2 sensors age, they will go "leaner", causing the computer to go richer. All the computer sees is what the sensor(s) tell them. If the car runs rich, it is harder/hotter on the cats. Winter grade fuel, or higher percentage of alcohol makes a difference also. Tire pressure will sneak up on you too. A heavy foot makes the most impact on gas mileage.
 
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