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    Thread: Bad oxygen sensor? Bad MPG .No CEL.

    1. Member lroy12's Avatar
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      08-02-2008 03:00 PM #1
      I had my oxygen sensors unplugged for two years and ran that way for two years and got 23 mpg city and 27 hwy (turbo).

      Would running rich for two years kill my car and or o2 sensors ?

      WHen i plugged my o2 sensors back in recently with a new chip, my MPG is very low (16ish) and my idle is a little rough. I have a A/f gauge tapped to the signal wire of the o2 sensor. Could this be causing an issue.

      I have no cel and no codes in my car. What do you think could be causing my bad MPG?




      Modified by lroy12 at 2:19 PM 8-2-2008


    2. Member Evo8nate's Avatar
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      08-02-2008 03:29 PM #2
      how long have they been plugged in for?

      let it throw a code

      it will haha


    3. Member lroy12's Avatar
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      08-02-2008 03:32 PM #3
      they have been plugged in since last weekend.. i have driven 100 miles with them

    4. Member Evo8nate's Avatar
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      08-02-2008 03:36 PM #4
      well i dont know about the a/f guages affect on it, but im sure the new chip contributed to the lowered mpg, in addition, the 02s are probably being "lazy"

      or on there way out, thats what happened to me before they threw a code, and mpg plummeted.

      they are currently still lazy, and the cel went off haha but i still have the ****ty mpg soo i would first eliminate the option of the a/f gauge being the problem by temporarly unplugging it, and seeing what happens, and go from there


    5. Member lroy12's Avatar
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      08-02-2008 03:43 PM #5
      well i hope the chip is not an issue. I was just running old C2 software for the last 2 years with o2 sensors unplugged.I recently upgraded and now i have the o2 sensors plugged in..

      I dont think the software is that different.


    6. Member lroy12's Avatar
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      08-02-2008 06:10 PM #6
      can the o2 sensor not be working properly and the CEL doesnt come on?

    7. Member GinsterMan98's Avatar
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      08-02-2008 07:31 PM #7
      First off your car is sick!!! Second, get a wide band asap, because your stock one and that a/f gauge are not telling you anything about your a/f ratio. Your stock o2 sensor is accurate to .5 afr if your lucky, were a wide band is accurate to .1 or better. For your o2 sensor, you need to replace it due to the rich afr's. To save the new one, get a standoff bung to keep it out of the exhaust stream so it can't see the added fuel. There are a couple places that sell standoff bungs, but I can't remember who. A piece of 3/4 inch about 1 inch long with a regular bung welded to it and then welded to the exhaust would work.
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    8. 08-02-2008 07:35 PM #8
      add-on bung or the ECU could be readapting and causing your car to rough with poor fuel economy.

      BTW, 42DD makes a add-on bung and plug kit.




      Modified by dubhaustuning.com at 4:43 PM 8-2-2008


    9. Member in5ane's Avatar
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      08-04-2008 11:25 PM #9
      Hey man, I have the same car and I know for a fact that I need an o2 sensor replacement. There is, and actually never has been, a CEL.

      Sounds like ur old sensors are failing and/or dirty and not sending a good enough reading so the ecu is trying to compensate by throwing in more fuel (causing that rough idle and of course the low mpg).

      That's at least what my german mechanic has told me, hope this helps.


      Modified by in5ane at 11:27 PM 8-4-2008

      Quote Originally Posted by thecorradokid24 View Post
      Do I get more say now that I own a mk2 as well?

    10. Member lroy12's Avatar
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      08-04-2008 11:27 PM #10
      Quote, originally posted by in5ane »
      Hey man, I have the same car and I know for a fact that I need an o2 sensor replacement. There is, and actually never has been, a CEL.

      Sounds like ur old sensors are failing and/or dirty and not sending a good enough reading so the ecu is trying to compensate by throwing in more fuel.

      You mentioned the bad mpg but how does it idle with the sensors plugged in??


      Hey thanks for the post
      I actually idle a little lumpy.. its not as steady as it once was.

      i thought it was a vac leak.. but you could be right it might be the o2..

      How do you know for a fact that you need new o2 sensors?


    11. Member in5ane's Avatar
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      89 Golf, 2002 Pathfinder, R.I.P. MK3 Golf :(
      08-04-2008 11:35 PM #11
      I know because I had somehow snapped one of the wires leading to the o2 sensor and was driving it like this for a little while and it would idle real rough, as in, 600-700 and then eventually stall.

      I've since replaced the harness/clip and now it idles at like 850-900 (but has not stalled again since).

      Mechanic tells me our cars have finicky o2 sensors and that its common.

      Quote Originally Posted by thecorradokid24 View Post
      Do I get more say now that I own a mk2 as well?

    12. Member lroy12's Avatar
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      08-04-2008 11:39 PM #12
      one of the wires on my harness side of the o2 sensor came out.. and its being held in with tape >_> thaat might have something to do with it.. and tat its probably covered in soot

    13. Member in5ane's Avatar
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      89 Golf, 2002 Pathfinder, R.I.P. MK3 Golf :(
      08-04-2008 11:42 PM #13
      definetly. Clean that up first and then let er run for a while. If its the o2 sensor then I'd bet it starts up fine and after she heats up it goes back to the lumpy idle.

      I'm looking all around for sensors since boshe's is like $160-200. Any universal is supposed to be ok as long as its a 4wire I believe. I'm leary of buying cheap parts for this car tho....

      Quote Originally Posted by thecorradokid24 View Post
      Do I get more say now that I own a mk2 as well?

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