New Help! both 02 sensors and no CAT
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This is a discussion on New Help! both 02 sensors and no CAT within the STi Technical Forum forums, part of the Tech & Modifying & General Repairs category; Well, I am brand new to this forum, I have a 05 STI with headers, up pipe, down pipe and ...

  1. #1
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    New Help! both 02 sensors and no CAT

    Well, I am brand new to this forum, I have a 05 STI with headers, up pipe, down pipe and NO CAT, the car also has the computer set at stage 2 with a COBB remapper...here is my problem. I have already replaced the Map sensor, via code, but I still have a code that tells me to replace the front 02 sensor, I am still running both front and back 02 sensors. I have not done that as yet, because I am not running a CAT, and that is the way I would like to leave the car. I have been told that running the car with no CAT will just keep burning up the 02 sensors, but I find that hard to believe. Is there anyone that can give me some help??? Really all that we are talking about are voltages, but I do not know the return voltage on either 02 sensor. I really do not want to put the CAT back in, because I am running a 3" JDM type all the way back and having to put the CAT back in would be a pain...of course it would not been any pain like changing the clutch like I did this past week-end and if any one needs help with that let me know. How about it ANY HELP?????
    thanks Jim

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  3. #2
    He simply abides. SD_GR's Avatar
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    When you said you replaced the MAP sensor via code, am I correct in assuming you in fact replaced the MAF sensor located on the air intake just past the air filter due to an error code P0171? This error typically reads something like "Bank 1 lean" and the usual suspects are the oxygen sensor, MAF, and so on?

    Does the car have an aftermarket intake? Aftermarket filter? BOV? FMIC or larger TMIC?

    How do you know the car actually isn't running lean in reality?

    Any staggering or hesitation or idle problems?

    See this link:
    http://forums.nasioc.com/forums/show...ighlight=P0171
    WRX Info Links, Courtesy TheJ
    The world breaks everyone and afterward many are strong in the broken places. Ernest Hemingway
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    Thank you for your reply

    OK, first the engine light just stays on now, even after you have disconnected the battery, it comes back on after about 30 seconds. We have checked the code and it is PO031, "front 02 heater control circuit". It was throwing P0103 "Mas air flow circuit"...did a pinpoint test using Subaru service manual and that showed faulty MAF sensor, so we replaced it. As far as the air box, I have taken the large section that runs into fender well off.....I am runing the stock top air filter section with a after market air filter inside. I am running the stock intercooler top mount.
    Running a after market blow off valve. As far as exhaust goes, I am running headers, up pipe with the front 02 sensor mounted in it, down pipe with the back 02 sensor mounted in it with 3" all the way back with muffler at back like stock.
    AS far as how the car is running....the car is NOT running real strong, and could very easily be lean, AND dies after it is fully warm as you stop. When the engine is cold RIGHT after you start, it idles fine. Like I said before I really do not want to put CAT back in, and will put new front 02 sensor in but am afraid that it might burn up like the stock one IF even if it is bad, but with the code that it is throwing, it must be bad.
    Thank you for any help.
    Jim

  5. #4
    He simply abides. SD_GR's Avatar
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    Quote Originally Posted by jtbarnet View Post
    OK, first the engine light just stays on now, even after you have disconnected the battery, it comes back on after about 30 seconds. We have checked the code and it is PO031, "front 02 heater control circuit".

    See

    http://forums.nasioc.com/forums/show...ighlight=P0171
    posted this morning from another STi user; you might follow the thread in case there are responses that help you. Also see
    http://forums.nasioc.com/forums/show...hlight=P0031It and
    http://www.wrxfanatics.com/lofiversi...hp/t21059.html
    and
    http://forums.nasioc.com/forums/show...ighlight=P0031



    was throwing P0103 "Mas air flow circuit"...did a pinpoint test using Subaru service manual and that showed faulty MAF sensor, so we replaced it.

    That CEL could come up if the MAF connections were faulty, the intake you are using is really rude to the ECU and/or has a hole or fault in it (check for vacuum leaks while you're poking around) or if you were to turn the key past the ACC position with the MAF harness disconnected.


    As far as the air box, I have taken the large section that runs into fender well off.....I am runing the stock top air filter section with a after market air filter inside. I am running the stock intercooler top mount.


    I am surprised you're not getting a P0171, they are much more popular CELs to throw with your mods. This isn't going to be an easy troubleshooting game. I would start by making sure the front O2 sensor is in fact connected correctly and securely, and working, and see if that helps at all. Check out the links above (including the OEM bracket vs. sensor wiring issue), others have done a bunch of stuff trying to figure it all out.
    Last edited by SD_GR; 07-27-2007 at 03:08 PM.
    WRX Info Links, Courtesy TheJ
    The world breaks everyone and afterward many are strong in the broken places. Ernest Hemingway
    I lied. I cheated. I bribed men to cover the crimes of other men. I am an accessory to murder. But the most damning thing of all... I think I can live with it. And if I had to do it all over again - I would. Benjamin Sisko
    DISCLAIMER: Opinions expressed are the author's alone and are inherently worthless.

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    Still need help

    Just changed flywheel and clutch this past weekend....I know that does not have anything to do with this, but have alredy checked wiring, checked voltage, The main thing that I am really concerned about is IF I replace front 02 sensor, I do not feel like the computer is still going to get a good reading front the back 02 sensor, because of having NO CAT, I hate to go out and buy a new front sensor and then have it do the same thing in a very short time...it is kinda hard to borrow from someone around in the Dallas area, because I relly do not know anyone that has a STI,,,,I am a middle age guy and really do not know any body else around the area with a car tht I can switch with and also am afraid that IF I do switch with someone it might burn their 02 up....any more ideas?????

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    If anyone needs clutch replacement help!!!

    I am going ahead and putting this out also, maybe I can help someone else with clutch, flywheel replacement in STI. There are 2 or 3 things that are listed in the Subaru manual that you DO NOT need to do. First FOLLOW the steps layed in the manual, BUT DO NOT REMOVE STEERING WHEEL SHAFT!!!! leave the steering in place...just pull axels out of trans and swing to side..DO NOT TAKE THEM OUT....and last make sure that you have a 6" bolt to remove the pinn that the clutch lever hangs on. If you will use a bolt about 4 or 5" long it will be easy to take a long large screw driver and kinda pry the bolt out far enough to get hold of it. ALSO you WILL NEED the engine suport that they talk about. I just used a piece of steel bar about 10" long, took a large washer, bolted it down to back of block where the manual showed and used the large bolt at back of firewall, slid it over the bolt, then I jacked the trans up as high as it would go, and welded the bar to the large washer. My 05 STI had about 40,000 and I had to take a chesel and hammer between block and trans to get it started and then just a lot of muscle. BE READY the trans is VERY heavy!!!! I did mine in the driveway, but used very large jack stands and got the car as high as I could. YOU CAN NOT DO THIS JOB BY YOUR SELF!!!! If anyone needs any more advice, just let me know. Clutch works great, but if you run a racing clutch, you will get some chatter, but that is very normal.
    HOW ABOUT SOME HELP WITH MY PROBLEM.....IS ANYONE RUNNING WITH OUT A CAT????? WHAT ABOUT 02 SENSORS PROBLEMS???????
    Thanks, Jim

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