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Old 05-01-2021, 11:04 PM   #1
Empresser
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Default Bad fuel economy.

So I bought a 2009 Impreza Outback Sport that gets worse fuel mileage than my 2001 Forester. The car itself is in excellent shape, just abysmal chugging. The car has 104k, spark plugs and wires were changed at 96K, air filter looks newish, Tires are almost brand spanking new, What else could be doing this mechanically? PCV valve clogged? Fuel filter? Timing belt will be done in a month of course.
Does the TPMS light trigger a fuel-air worse fuel-air ratio?
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Old 05-01-2021, 11:22 PM   #2
Gucciflipflops
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Not too well versed on NA Subaru engines nor that year or model but Generally under inflated tires do consume a little more fuel.

How bad of a difference is your fuel consumption?
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Old 05-02-2021, 02:02 PM   #3
Bluefoton
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There is no TMPS-related "trigger". Also, gas mileage is a resultant of many, many factors - it's really hard to say if anything is wrong. Headwind, ambient temperature, tyre pressure, elevation, inclination, trip duration, speed profile (the actual curve of speed vs.time), acceleration, deceleration (amount of stops, red lights, braking vs. coasting), cargo load, MT vs AT, ethanol percentage in the fuel... all of those yield the ultimate "mpg" value.
The engine is nearly the same: the Forester had the EJ251, the OBS has the EJ253 which is a little bit more economical. The OBS is also more aerodynamic as opposed to the boxy Forester.

If you want to compare yourself to others, have a look at Fuelly, and look at 2008-2001 imprezas (2.5i, premium, OBS...). Averages hover around 24-25mpg, but uou also see the entire statistical distribution.

https://www.fuelly.com/car/subaru/im...ubmodel_id=115

Mind you, with a 2009 that you have just bought, you do need to check a few things (if you didn't already). Maintenance records, spark plugs, tire pressure, brakes, air filter, vacuum leaks, etc.

Last edited by Bluefoton; 05-02-2021 at 02:25 PM.
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Old 05-02-2021, 02:38 PM   #4
10AWSE
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What mpg are you currently getting? I get about 25 mpg at 70 mph highway driving with my 99 Legacy SUS 2.5 Liter.
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Old 05-03-2021, 01:33 PM   #5
yarrgh
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Could be a non-engine factor, such as a dragging brake.
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Old 05-06-2021, 03:17 PM   #6
Empresser
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Quote:
Originally Posted by yarrgh View Post
Could be a non-engine factor, such as a dragging brake.
Good point... I'll check that out too.

Thanks for all the replies guys. Sorry, haven't had a chance to check back here in a few days.

I just had all 4 shocks replaced with KYB, but the bad fuel economy persists.
Here's what I know:

I had the tires inflated to spec with nitrogen at the dealer a few weeks ago, so even though the TPMS light is on, I'm pretty sure they're not underinflated. It's nothing obvious while driving, anyway.


Spark plugs that were replaced @96K by Christian Bros. automotive for the prev. owner were NGK 5464 Iridiums. The Owner manual calls for NGK 5463 Laser Platinums. Wrong heat range plug maybe?

Where is the PCV valve located in this car? is it the same on top as an EJ-25 motor from 2001? I want to check that first.

Thanks again.
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Old 05-07-2021, 10:34 AM   #7
Empresser
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Anyone here? Where did you guys go?
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Old 05-09-2021, 07:58 PM   #8
Suba Imp 10
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top passenger below throttle body and coil pack
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Old 05-11-2021, 04:11 PM   #9
Vancouver98STi
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V4 GF8 White

Lightbulb Check if one rotor gets hotter than the others

Quote:
Originally Posted by yarrgh View Post

Could be a non-engine factor, such as a dragging brake.
I was suspicious of dragging brakes... so after a short drive, I touched each rotor through the wheel with the knuckle of one of my fingers. I quickly found the culprit. Turns out one rear caliper seal was torn, and this had allowed water to enter and corrode the piston (which had become semi-stuck in the bore).
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Old 05-12-2021, 03:40 PM   #10
Lega-C
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Could be you need a new maf or vacuum leak. No CEL present?
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Old 05-12-2021, 10:00 PM   #11
Empresser
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Quote:
Originally Posted by Lega-C View Post
Could be you need a new maf or vacuum leak. No CEL present?
No CEL
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Old 05-12-2021, 10:01 PM   #12
Empresser
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Quote:
Originally Posted by Suba Imp 10 View Post
top passenger below throttle body and coil pack
Not sure I follow you. Check the throttle body and the coil pack? Is that what you mean?
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