Horrible Gas Mileage?
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This is a discussion on Horrible Gas Mileage? within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Hey guys, sorry if this isn't the right place for this... I am getting horrible gas mileage on my '02 ...

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    Horrible Gas Mileage?

    Hey guys, sorry if this isn't the right place for this...

    I am getting horrible gas mileage on my '02 WRX. When I bought it it was fully stock. Only mods done was a downpipe/catback (problem was still there when stocked, though). It is getting less then, but about 200 miles on a tank of gas. Last time I filled up I calculated it to be roughly 12MPG.

    I honestly don't push the car as far as acceleration. I am gentle on the peddle and rarely ever push it. I do drive in city but stops are few and far between. The only thing I was thinking was that there's something up with the front O2 sensor or do you think aging spark plugs could make that big of a difference (haven't checked/changed them yet since I just bought the car, probably have never been changed)?

    I don't have any service lights and everything from a visual standpoint looks normal to me. Any suggestions would be appreciated.

    Thank you!

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    Registered User oguitar's Avatar
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    I bet it is the o2 sensor. Spark plugs would cause more serious problems. Still need to change them though.
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    Moderator T0rque's Avatar
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    Spark plugs and fuel filter is usually changed every 30k.


    Lead Wrench @ WTF Tuning, LLC

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    The Default One SeattleJeremy's Avatar
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    How many miles on the car?
    How many miles have you put on the car sense purchase?
    Is the maintenance up to date?
    Is it leaking fuel?
    Are you calculating the mileage correctly?
    Is the check engine light on?


    Are you sure it's not riding on chromed out 20's, with an aluminum wing mounted for Drift mode?

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    Administrator RayfieldsWRX's Avatar
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    I know you said that you don't push it, but driving style makes a large difference to the mpgs of these cars. Under normal acceleration, at what rpms do you shift, and about how far down do you think you press the pedal? (25%, 50%, etc)

    Having said all of that, 12mpg is a sign to me that something's really wrong, regardless of driving style. I'm getting twice that on a somewhat modded 2002...and contrary to popular belief I do put the power down here and there.
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    UnBanned Sinister's Avatar
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    Read the Gas Mileage sticky for a little help:
    Gas Mileage FAQ

    With that being said, O2 sensor is a common problem on older imprezas. cheap, and easy to replace. I'd start there.
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    Registered User teflon_jones's Avatar
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    What kind of tune are you running on it?

    Lots of possible causes as mentioned above. An OBDII scanner might help narrow it down.
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    Don't know, some of us might be unlucky, perhaps it's just the car and particular engine. I have a new stock 2010 hatch, 5K miles, drive very light footed, rarely open it up, cruise at 65 on the highway, I get only teens to low twenties tops all around. Others claim to get much more. If I cruise 70-80, mileage drops to 18 or so. Most cars I have had I usually get much more than EPA, not so with this WRX- and it runs perfect.

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    Moderator T0rque's Avatar
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    Driving style is huge with these cars my first 05 I'd see only 11-13 mpg..

    You said you had a downpipe.. Do you have engine management?


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    Quote Originally Posted by teflon_jones View Post
    What kind of tune are you running on it?
    Quote Originally Posted by LPPTundWRX View Post
    You said you had a downpipe.. Do you have engine management?
    These are good ideas to bring up, along with having a bad o2 sensor. If you don't have a tune or you have a tune that's too rich, you can easily get really bad gas mileage since the fuel isn't burned off efficiently. For example, if you don't have a tune at all, the stock ECU could easily be trying to overcompensate for any sort of detonation you might be getting with just your downpipe/catback problem, resulting is bad gas mileage. In my experience, a good tune will often actually improve gas mileage since the fuel is burned off more efficiency, but of course that gets negated because people often like to step on it more often now that more power has been freed up.
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    Registered User TurnWRX's Avatar
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    12's quite low. I have an 03 wrx, and back when it was stock, I got 16 mpg city driving and that's in a major metropolitan area with lots of hills, stoplights, and stop signs.

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    Thanks for the responses guys, had a long day at work, sorry for not answering some of these questions...

    I bought the car after some rich guy had it sitting outside for two years probably not knowing what the car was. The bottom was pretty rusty but nothing too serious but I KNOW that he didn't keep up to date on some repairs...

    When I got the car it was in that diagnostics mode (green clip under dash was still together) and before I knew of that diagnostics/anti theft mode I was worried because it would ding 6 CEL's but all that went away as soon as I separated the clips.

    No, I don't have any engine management system, yet. But the bad gas mileage was actually happening just the same as before the cat-back was put on. It's currently running on 72k miles I bought it at 68k miles. I changed the air filter and always pump premium and put fuel injector cleaner in it regularly. I recently took out the rear O2 sensor and did the resistor mod to it so no, it has no CEL.

    Is there any way to check the front O2 sensor without replacing it? I bought a front O2 sensor when I thought it needed it from that "diagnostics/anti theft" whatever mode but was actually going to sell it (140 bucks isn't much, but if not needed I don't want to hold onto it.)

    Thanks again for all input and further suggestions!

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