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Discussion Starter #1
So for the last 3 tanks I've gotten worse mpg, 2 or more. Calculated, the mpg gauge is 3 or 4 optimistic anyway. I drive exactly the same, buy the same 93 octane at the same place. Stock 2018,no mods other than a K&N panel in the box and Nameless muffler deletes, both have been on for 5000 miles or so. I can also hear the turbo more, pronounced sucking air sound, which is cool but wondering why now and not before. Car has 11500 miles. No check engine light and no codes so I don't think there's a vacuum or boost leak, and everything is visually fine. Any thoughts?
 

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either that or something else is different or wrong . . .:rolleyes:

100% normal for the rest of us
 

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Who told you to put a K&N high flow panel filter? The stock OE tune already runs lean up top.


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So for the last 3 tanks I've gotten worse mpg, 2 or more. Calculated, the mpg gauge is 3 or 4 optimistic anyway. I drive exactly the same, buy the same 93 octane at the same place. Stock 2018,no mods other than a K&N panel in the box and Nameless muffler deletes, both have been on for 5000 miles or so. I can also hear the turbo more, pronounced sucking air sound, which is cool but wondering why now and not before. Car has 11500 miles. No check engine light and no codes so I don't think there's a vacuum or boost leak, and everything is visually fine. Any thoughts?
The threshold for CEL is so high that I wouldn't rely on just the light to show up. I've had a number of boost leaks and vacuum leaks (still chasing an exhaust leak down that's giving me a false lean now) that never triggered a CEL, but would show up big time on a Cobb AP or OBDII streaming device when looking at LTFT (AF Learning).

Buy a OBDII device that can stream live ECU data, such as the BlueDriver, though there are much cheaper options. Just make sure it will save your reports, because it's hard to drive and look at the device to track the issues. Better to look at the log on your computer after driving. Make sure to record RPM, intake manifold pressure, MAF sensor, LTFT, and maybe even coolant temps and STFT.
 

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Discussion Starter #8
I'm used to European cars that throw the light for no reason at all. I guess I'll hook up the scanner, I work at a dealership. Thanks
 

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Did you just change over to winter tires? Your engine finally breaking in? Winter gas blends? Using heat seats+heater+windshield heater/wiper+headlights will drain more energy use more gas.

Tiny mileage your car is pretty much brand new you'll see changes still. Have almost 100,000km on MY18 STI plenty of noises come and go.
 

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It is likely the gas changed to a winter blend, like Boilermaker mentioned above, is the cause of the MPG change.
 

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Discussion Starter #12
Again, thanks for the input but this is the third winter with this car and it didn't drop like this before. Also, it's not even that cold here yet.
 

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It could literally be anything. Maybe your air filter is dirty? A boost leak would cause the engine to run rich. Different blends of gas. 2 mpg is not a whole lot tbh and our gauges aren't that accurate to begin with.
 
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