Sudden gas mileage problems.
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This is a discussion on Sudden gas mileage problems. within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Few months ago, I had to drive off a side walk, figured i'd have enough clearance but no, right in ...

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    Sudden gas mileage problems.

    Few months ago, I had to drive off a side walk, figured i'd have enough clearance but no, right in the middle of the car a heard a crunch. Ever since my gas mileage has suffered serverly, I used to get 29mpg on the highway, now I'm somewhere around 15-17. Finally got a chance to crawl under the car today to inspect for damage. Fallowing pic was the only damage I could find.

    Anybody have any ideas?

    Sorry If this has been covered, I couldn't find it, if it has a redirection would be appreciated.

    Thanks all in advance.
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    Registered User EvoEatr's Avatar
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    Quote Originally Posted by NFACurious View Post
    Few months ago, I had to drive off a side walk, figured i'd have enough clearance but no, right in the middle of the car a heard a crunch. Ever since my gas mileage has suffered serverly, I used to get 29mpg on the highway, now I'm somewhere around 15-17. Finally got a chance to crawl under the car today to inspect for damage. Fallowing pic was the only damage I could find.

    Anybody have any ideas?

    Sorry If this has been covered, I couldn't find it, if it has a redirection would be appreciated.

    Thanks all in advance.

    Hmmm How many miles are on the vehicle? I find it hard to believe that a simple dent in the cat. / heat shield would cause your fuel consumption to increase that much...Are you sure you aren't having any other problems with the vehicle? Is the CEL illuminated? Are you sure there wasnt any other damage done?

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    I'm over the 100k mark for sure, I think somewhere around 120k. Thats all the damaged I found by crawling under the car. CEL is not on and no error codes were found by my buddies code reader. I'm starting to wonder if the O2 sensor is going bad, there are no leaks, and no smell of gas in the engine compartment running or not. His code reader couldn't perform an O2 sensor check.

    I'm stumped..

    Thank you very much for takeing interest in my post EvoEatr!
    Last edited by NFACurious; 04-04-2010 at 06:43 PM. Reason: props for EvoEatr

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    Registered User EvoEatr's Avatar
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    Quote Originally Posted by NFACurious View Post
    I'm over the 100k mark for sure, I think somewhere around 120k. Thats all the damaged I found by crawling under the car. CEL is not on and no error codes were found by my buddies code reader. I'm starting to wonder if the O2 sensor is going bad, there are no leaks, and no smell of gas in the engine compartment running or not. His code reader couldn't perform an O2 sensor check.

    I'm stumped..

    Thank you very much for takeing interest in my post EvoEatr!
    no prob man... at that kind of mileage the first thing that comes to mind is service history have u ever had a tune up on the vehicle? fuel filter plugs etc etc?? Usually if there is a prob with the o2 sensor it will throw a code....However that was also my first thought...

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    Quote Originally Posted by EvoEatr View Post
    no prob man... at that kind of mileage the first thing that comes to mind is service history have u ever had a tune up on the vehicle? fuel filter plugs etc etc?? Usually if there is a prob with the o2 sensor it will throw a code....However that was also my first thought...
    No, All I have done has been with Subaru's recomended maintenance, nothing major, got the car at 70k, in the glove box was records of dealership maintenance to the T, oil changes everything done at the dealer. All I've had done (forgive me, machinist, not a mechanic so if I'm not totally savvy on part names etc) is the timing belt spark plugs, and a radiator hose that busted 3rd day I had the car.

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    Registered User 06scoobyrex's Avatar
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    Check plugs, o2 sensor, clutch might be going out or tranny
    Hawk-Eye Alliance #801
    The Impreza "this was repaired/replaced at what mileage" database (Please Contribute)
    http://www.clubwrx.net/forums/showth...57#post2688257

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    Quote Originally Posted by 06scoobyrex View Post
    Check plugs, o2 sensor, clutch might be going out or tranny
    Will get the o2 sensor checked, plugs should be good, less than 15-20K (?) on them, clutch still feels very strong. How hard is it to get the plugs out for a visual inspection? Anyway to test a clutch?


    Thanks again everyone.

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    Registered User EvoEatr's Avatar
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    Quote Originally Posted by NFACurious View Post
    Will get the o2 sensor checked, plugs should be good, less than 15-20K (?) on them, clutch still feels very strong. How hard is it to get the plugs out for a visual inspection? Anyway to test a clutch?


    Thanks again everyone.

    If the clutch isnt slipping, I highly doubt its the clutch...hydraulic clutch so obviously no need for adjustment ( not that it should be out of adjustment and dragging or something)... The plugs I personally would never ever remove for visual inspection on these cars, their so cheap and theres only 4 of them I would definitely replace with new... The plugs can be a good hint of how the car is running though, lean, rich, burning something etc etc...If you have the means I would grab a decent scanner and monitor o2 sensor activity and ST fuel trim and LT fuel trim...

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    Quote Originally Posted by EvoEatr View Post
    If the clutch isnt slipping, I highly doubt its the clutch...hydraulic clutch so obviously no need for adjustment ( not that it should be out of adjustment and dragging or something)... The plugs I personally would never ever remove for visual inspection on these cars, their so cheap and theres only 4 of them I would definitely replace with new... The plugs can be a good hint of how the car is running though, lean, rich, burning something etc etc...If you have the means I would grab a decent scanner and monitor o2 sensor activity and ST fuel trim and LT fuel trim...


    Ok, I understand o2 sensor activity, communications from the sensor to the ECU, ST and LT fuel trims... no idea

    I never ever ever run anything but 93 octane in this car. By looking at the plugs, how can I tell if its running rich vs. lean. I'd imagine that excessive fuel useage would be a car running rich.

    (P.S. I read Ross-Tech: VAG-COM: Fuel Trim Info , and I'm still kinda confused about trims. I now understand about the trim being the ecu's adjustment to the components that effect a/f ratio to produce more ideal situations though.)

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    Registered User EvoEatr's Avatar
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    Quote Originally Posted by NFACurious View Post


    Ok, I understand o2 sensor activity, communications from the sensor to the ECU, ST and LT fuel trims... no idea

    I never ever ever run anything but 93 octane in this car. By looking at the plugs, how can I tell if its running rich vs. lean. I'd imagine that excessive fuel useage would be a car running rich.

    (P.S. I read Ross-Tech: VAG-COM: Fuel Trim Info , and I'm still kinda confused about trims. I now understand about the trim being the ecu's adjustment to the components that effect a/f ratio to produce more ideal situations though.)
    This is just a quick little chart I picked up on a google search... http://i271.photobucket.com/albums/j...mk/Plugs-1.jpg ...like you mentioned your 100% sure you have no fuel leaks so the excess fuel must be in the combustion...I'm just kind of surprised with a sharp drop like that in fuel economy that the o2 sensor or something hasnt picked up on it..

    pretty good read by the way, thanks for the link...
    Last edited by EvoEatr; 04-05-2010 at 06:26 PM.

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    Registered User 06scoobyrex's Avatar
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    Quote Originally Posted by NFACurious View Post
    Will get the o2 sensor checked, plugs should be good, less than 15-20K (?) on them, clutch still feels very strong. How hard is it to get the plugs out for a visual inspection? Anyway to test a clutch?


    Thanks again everyone.
    its pretty easy just take out the battery airpump, snorkle, airbox and intake hose then undo the coilpacks then remove the spark plugs... it only takes like an hour or so... to check the clutch go 30mph and have it in 3rd and let off the gas completely then punch it if your rpms go up and the car hardley moves then its slipping but if it gives a normal response then its fine...
    Hawk-Eye Alliance #801
    The Impreza "this was repaired/replaced at what mileage" database (Please Contribute)
    http://www.clubwrx.net/forums/showth...57#post2688257

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    Quote Originally Posted by EvoEatr View Post
    This is just a quick little chart I picked up on a google search... http://i271.photobucket.com/albums/j...mk/Plugs-1.jpg ...like you mentioned your 100% sure you have no fuel leaks so the excess fuel must be in the combustion...I'm just kind of surprised with a sharp drop like that in fuel economy that the o2 sensor or something hasnt picked up on it..

    pretty good read by the way, thanks for the link...
    I'll have a little problem judgeing on those pics, I have the Bosch platinum 4 prong ones in mine. It may be my daily driver, and I might be suffering due to the currect economic situation, but I always put quality products in my car. If I can't get to work, I can't afford to provide her something to drink...

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    Quote Originally Posted by NFACurious View Post
    I'll have a little problem judgeing on those pics, I have the Bosch platinum 4 prong ones in mine. It may be my daily driver, and I might be suffering due to the currect economic situation, but I always put quality products in my car. If I can't get to work, I can't afford to provide her something to drink...
    you using platinum? i made that mistake in mine and i was getting pretty bad mileage then i put some ngk iridium plugs in them now it runs a lot better and has a hell of a lot more power now...
    Hawk-Eye Alliance #801
    The Impreza "this was repaired/replaced at what mileage" database (Please Contribute)
    http://www.clubwrx.net/forums/showth...57#post2688257

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    Registered User EvoEatr's Avatar
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    Quote Originally Posted by NFACurious View Post
    I'll have a little problem judgeing on those pics, I have the Bosch platinum 4 prong ones in mine. It may be my daily driver, and I might be suffering due to the currect economic situation, but I always put quality products in my car. If I can't get to work, I can't afford to provide her something to drink...

    I can also say that Subarus are extremely touchy when it comes to certain aftermarket components, axles,thermostats, ignition components etc etc...I have seen brand new aftermarket plugs and wires cause dead misfires on subarus before...not saying this is your problem just thought I would mention it...

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    Quote Originally Posted by 06scoobyrex View Post
    its pretty easy just take out the battery airpump, snorkle, airbox and intake hose then undo the coilpacks then remove the spark plugs... it only takes like an hour or so... to check the clutch go 30mph and have it in 3rd and let off the gas completely then punch it if your rpms go up and the car hardley moves then its slipping but if it gives a normal response then its fine...
    Maybe I should invest in one of those books, I used to be real into cars years ago, but machinework and the lack of desire to understand engines took over, because I read that comment and all I can say is... whaaa? Nothing against 06scoobyrex, its all my ignorance.

    Havening witnessed a slipping clutch in my first car, honda '92 accord dx (I miss that ride, 40mpg on the highway) My wrx 30 mph in 3rd has no hesitation on acceleration.

    Sorry It took me too long to respond 06scoobyrx, but yes I have the platinum ones, what are the iridiums costing???

    When they pulled my plugs to change the new ones, I asked and they reported "normal wear"..

    So now my deductions of problems leads me to, a bad o2 sensor that for some reason should be throwing a code but isn't, a crappy set of plugs that should have lasted longer than this and should not have failed so suddenly, or somehow that minor injury to the cat shield caused troubles up the line to the engine (waste gate etc) that being the first time under that car I could not identify...

    Am I crazy? I feel like going crazy and pulling all my hair out...

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