02 WRX lean codes and misfire problem
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This is a discussion on 02 WRX lean codes and misfire problem within the General Maintenance, Troubleshooting & Accidents. forums, part of the Tech & Modifying & General Repairs category; Alright, I'll start out with some back story on the car. It is a 2002 WRX wagon Automatic transmission that ...

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    02 WRX lean codes and misfire problem

    Alright, I'll start out with some back story on the car. It is a 2002 WRX wagon Automatic transmission that I bought about 4 months ago from a used car dealer. It has a short ram intake and cone filter on it and what looks to be a catless downpipe but I am not sure. I drove it for about 3 months around town, including a 500 mile trip that was all highway driving. About a month ago the car got a lean code that would come and go but the car ran just fine so I checked for vacuum leaks and upon finding none I pretty much ignored it. One day after running lean for a couple weeks it just started to misfire like crazy and would barely run, the car had no power at all. Upon resetting the ECU the car will continue to run good until both long term and short term fuel trims climb almost to 25% and then as soon as the check engine light comes on for a misfire code the car will barely run again, with the engine shaking badly. I've since replaced the spark plugs with standard NGK's, checked every hose and seal for a vacuum leak, cleaned and then replaced the MAF, checked compression and leakdown on all cylinders which came back good, checked and clean all the grounds in the engine compartment, checked the coil packs and connectors and they all seem fine. I would love it if someone could point me in which direction to check next because I am running out of ideas. I can also post pictures of anything on the engine if you want to look at them and I think I have the freeze frame data from the misfire codes here somewhere if I can find it. Any help or suggestions would be appreciated.

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    OMG WTF MainFrame's Avatar
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    What tune are you running? You can't expect to put an aftermarket intake on a Subaru with a stock tune and expect it to run right.

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    Quote Originally Posted by MainFrame View Post
    What tune are you running? You can't expect to put an aftermarket intake on a Subaru with a stock tune and expect it to run right.
    That's one of my problems, I bought the car with the intake already on it so I'm not sure if it has a tune or not and I don't have any way of checking it.

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    OMG WTF MainFrame's Avatar
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    Sounds like you need to research reputable Subaru tuners in your area and take your car in..

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    Quote Originally Posted by MainFrame View Post
    Sounds like you need to research reputable Subaru tuners in your area and take your car in..
    I don't think though that just an intake without a tune would cause the car to barely even run, with no power and horrible shuddering misfires. The tune may be a contributing factor but something more has to be going on with it.

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    OMG WTF MainFrame's Avatar
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    Intake without a tune can destroy the engine entirely.. so, there's that.



    You're right though, it may have already broken something internally.
    Last edited by MainFrame; 04-07-2013 at 02:33 PM.

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    Well I know it is not a mechanical issue as it only happens when the check engine light comes on and then it flashes and misfires. Once the ECU is reset it goes back to running nicely for a little bit so it must be electrical or maybe a sensor.

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    Registered User nsibanez's Avatar
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    This isn't a Mitsu. Our cars basically need a tune for almost anything whereas an EVO might have a CEL for a few miles before the ECU relearns itself.
    Our cars need a bit more care

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    Quote Originally Posted by techguy13 View Post
    Well I know it is not a mechanical issue as it only happens when the check engine light comes on and then it flashes and misfires. Once the ECU is reset it goes back to running nicely for a little bit so it must be electrical or maybe a sensor.
    Take a picture of the intake. Article for you to read and a sticky link.
    Cobb intake article
    IF YOU HAVE A MISFIRE CODE ,PLEASE READ THIS!!!

    It's barely running because you are maxing out the fuel trims and putting the car into limp mode. I would highly advise you stop driving the car until you find the issue. If it's having to add that much fuel then you either have a major vacuum leak somewhere or the intake inner diameter is WAY to big. Also it should be pretty obvious if you have a catless downpipe or not. All you have to do is look at the downpipe.

    Quote Originally Posted by nsibanez View Post
    This isn't a Mitsu. Our cars basically need a tune for almost anything whereas an EVO might have a CEL for a few miles before the ECU relearns itself.
    Every single OBDII car has the ability to "relearn". Thats why Subaru has DAM/IAM,fine/feedback knock correction and short/long fuel trims. The EVO's have the same issues as any other MAF based car does.
    Last edited by Donkey; 04-08-2013 at 05:08 AM.
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    Registered User nsibanez's Avatar
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    Gotchya. Thanks for the correction
    I can always count on youto school me on something

    Why would a vacuum leak cause more added fuel though if you don't mind me asking?

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    Moderator Donkey's Avatar
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    Quote Originally Posted by nsibanez View Post
    Gotchya. Thanks for the correction
    I can always count on youto school me on something

    Why would a vacuum leak cause more added fuel though if you don't mind me asking?
    The MAF sensor measures the air at the airbox/intake. Any leak post MAF,while the car is under vacuum,is going to pull un-metered air into the system. The oxygen sensor is going to pick that up as the AFR will not be correct. It tells the ECU to adjust,as it should,and add more fuel. The issue is this operation only happens in closed-loop fueling and there is not some infinite correction. 25% is the max the ECU can correct. In open-loop fueling (IE: high load/boost) oxygen sensor feed back is not used and the ECU will not correct for any un-metered air entering or leaving the system. There is no correction and the ECU is relying completely on the MAF sensor operation.
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    Registered User nsibanez's Avatar
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    Alright, I think I got it now. Thanks for that lesson

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    Quote Originally Posted by Donkey View Post
    Take a picture of the intake. Article for you to read and a sticky link.
    Cobb intake article
    IF YOU HAVE A MISFIRE CODE ,PLEASE READ THIS!!!

    It's barely running because you are maxing out the fuel trims and putting the car into limp mode. I would highly advise you stop driving the car until you find the issue. If it's having to add that much fuel then you either have a major vacuum leak somewhere or the intake inner diameter is WAY to big. Also it should be pretty obvious if you have a catless downpipe or not. All you have to do is look at the downpipe.
    I haven't been driving it at all because I was worried it would make the problem worse.

    Here is a picture of the intake
    Click image for larger version. 

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    And here is one of the downpipe
    Click image for larger version. 

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    Moderator Donkey's Avatar
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    That intake looks like a $30 Ebay special. No bueno. You don't want a bend right in front of the MAF and I doubt that is the correct I.D. Most just use 2.75-3" piping as that is common and cheap. The stock housing uses a 65mm orifice for the MAF housing. That is roughly 2.6 inches. That looks like an HKS downpipe. No offense,but if you can't tell there is no catalytic convertor (unless someone welded one on farther down the pipe under the car) then your eyesight is as bad as Stevie Wonder's is .

    Catted aftermarket:




    uncatted aftermarket:




    stock compared to aftermarket catted:

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    Quote Originally Posted by Donkey View Post
    That intake looks like a $30 Ebay special. No bueno. You don't want a bend right in front of the MAF and I doubt that is the correct I.D. Most just use 2.75-3" piping as that is common and cheap. The stock housing uses a 65mm orifice for the MAF housing. That is roughly 2.6 inches. That looks like an HKS downpipe. No offense,but if you can't tell there is no catalytic convertor (unless someone welded one on farther down the pipe under the car) then your eyesight is as bad as Stevie Wonder's is .
    Well my eyes are kinda ****ty, hehe. I just wasn't sure if there was supposed to be one there or further down but now I know. So do you think I should try and find a stock airbox to put on there or get a better aftermarket intake? Also would the lack of cats and the fact that I'm not sure if it is tuned or not be causing a big problem?

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