front 02 sensor disconnected, bad mileage!!!please help!!!
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This is a discussion on front 02 sensor disconnected, bad mileage!!!please help!!! within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; hey guys i need some help i bought a 2006 wrx a week ago, the guy i bought it from ...

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    front 02 sensor disconnected, bad mileage!!!please help!!!

    hey guys i need some help i bought a 2006 wrx a week ago, the guy i bought it from said his tuners disconnected his front o2 sensor because of the tune he did, he showed me where the front sensor was disconnected thats why the engine light is on, should i take it to the dealership so they can fix it? all i would have to do is reconnect it and resest the ecu right? please help guys

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    Registered User MainFrame's Avatar
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    Sounds like a bad tune.. who was the tuner, and what mods does the car have?


    There could be a few things going on. If the sensor was bad then it would be making inappropriate corrections in closed loop fueling. Could be poor MAF scaling, or leaks, injector problems, etc.. Whatever the case, sounds likely that you are going to need a tune by someone who knows what they're doing. Unplugging the front O2 sensor effectively disables closed loop and will cause poor fuel economy (as you have seen). Any decent tune for a street driven WRX is going to need a working front O2 sensor.

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    Quote Originally Posted by MainFrame View Post
    Sounds like a bad tune.. who was the tuner, and what mods does the car have?


    There could be a few things going on. If the sensor was bad then it would be making inappropriate corrections in closed loop fueling. Could be poor MAF scaling, or leaks, injector problems, etc.. Whatever the case, sounds likely that you are going to need a tune by someone who knows what they're doing. Unplugging the front O2 sensor effectively disables closed loop and will cause poor fuel economy (as you have seen). Any decent tune for a street driven WRX is going to need a working front O2 sensor.
    I asked a place here in San Antonio and they told me it would be $450 for the tunning plus $90/hr to reconnect the o2 sensor, and yes im not getting 26mpg on highway im getting 17mpg. My mechanic is gonna do all the maintenance this weekend he told he could reconnect the o2 sensor and resest the ecu so see how it runs. It bothers me so much to see the engine light and the cruise control flashing all the time.

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    Registered User Ingo's Avatar
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    Yes, get the maintenance done and re-connect the sensor. I had it go bad and it was bad in several ways... As MainFrame said, the front O2 sensor is needed. Get a tune, I'm not sure about what's available and at what cost. RESEARCH here, use the search function in the upper right, ask...
    You can't have everything - where would you put it?

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    Quote Originally Posted by Ingo View Post
    Yes, get the maintenance done and re-connect the sensor. I had it go bad and it was bad in several ways... As MainFrame said, the front O2 sensor is needed. Get a tune, I'm not sure about what's available and at what cost. RESEARCH here, use the search function in the upper right, ask...
    Got the maintaince done, gonna set up an appointment with a tuner shop where I live, but am I able to drive it while I wait to get it tuned?

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    Registered User Ingo's Avatar
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    Nobody can really tell. You may have to constantly re-set the ECU just to keep it from running too lean or rich. As it re-learns with probably wrong readings and the engine starts to run poor - then you need another reset. I hope the defaults that the freshly reset ECU uses will work for the time. But it's certainly not safe to operate this way. If possible I'd park it and use another car. I know, may be hard to do. I'm in a better position, I have my Ram truck that's really there to tow my camping trailer and that's the only reason I have it. But I've used it as back-up vehicle when needed.
    You can't have everything - where would you put it?

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    Quote Originally Posted by Ingo View Post
    Nobody can really tell. You may have to constantly re-set the ECU just to keep it from running too lean or rich. As it re-learns with probably wrong readings and the engine starts to run poor - then you need another reset. I hope the defaults that the freshly reset ECU uses will work for the time. But it's certainly not safe to operate this way. If possible I'd park it and use another car. I know, may be hard to do. I'm in a better position, I have my Ram truck that's really there to tow my camping trailer and that's the only reason I have it. But I've used it as back-up vehicle when needed.
    I had it tuned to stock, I haven't noticed a difference before they tuned it

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    Registered User Ingo's Avatar
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    So you got it tuned to stock and reconnected the sensor? What other changes had been done to the car? Can those be run on a stock tune?
    I'm on a stage 2 TP tune, and the front O2 sensor is there and operating. It went bad and the engine started running bad, then worse, then reset ECU and it was fine for a little while, then CEL came back with sh!tty running engine, reset and at least got home. Had to replace sensor. Drove truck. After replacement no more issues. Moral: a tune that deletes that sensor can't possibly be right. That sensor is needed. If it was disconnected, it needs to be re-connected. That's assuming it's OK. If the sensor was disconnected because bad (it's $200!) well, you'll find out and spend the money... If your car is not modified, you'll be OK with the stock tune, or look for a stage 1 tune. If modded, like cold air intake and such, you'll need to tune for that. And until it's knowb what mods there are nobody can tell if there's any safe way of running it.
    You can't have everything - where would you put it?

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    Quote Originally Posted by Ingo View Post
    So you got it tuned to stock and reconnected the sensor? What other changes had been done to the car? Can those be run on a stock tune?
    I'm on a stage 2 TP tune, and the front O2 sensor is there and operating. It went bad and the engine started running bad, then worse, then reset ECU and it was fine for a little while, then CEL came back with sh!tty running engine, reset and at least got home. Had to replace sensor. Drove truck. After replacement no more issues. Moral: a tune that deletes that sensor can't possibly be right. That sensor is needed. If it was disconnected, it needs to be re-connected. That's assuming it's OK. If the sensor was disconnected because bad (it's $200!) well, you'll find out and spend the money... If your car is not modified, you'll be OK with the stock tune, or look for a stage 1 tune. If modded, like cold air intake and such, you'll need to tune for that. And until it's knowb what mods there are nobody can tell if there's any safe way of running it.
    Yes I did I had my mechanic reconnect and it and then took it to the tune shop to tune it back to stock.and no other changes. And I think so the runner would've told me if I couldn't. The car is pretty much stock besides the exhaust and bov, and a grim speed solenoid

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    Registered User frenziedcage's Avatar
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    Quote Originally Posted by MainFrame View Post
    Sounds like a bad tune.. who was the tuner, and what mods does the car have?


    There could be a few things going on. If the sensor was bad then it would be making inappropriate corrections in closed loop fueling. Could be poor MAF scaling, or leaks, injector problems, etc..

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