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Rough running, O2 sensor? 900 1994

posted by  yrots on  Wed Jun 10 15:39 CST 2009
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last visit: Sat Apr 12 11:19 CST 2014
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94 NA 940 Rex/Regina 140K I was driving home from work (20 minutes highway speeds) after entering my neighbourhood I had to go over several speed humps. Suddenly the car began to run very rough as if starved for fuel or missing spark. I limped along about 1/4 mile and then stopped to look under the hood while running to see if anything had come loose.(wires,hoses). I looked under the car and saw the cat slightly glowing orange which surprised me. Shut the car down to cool before limping the rest of the way home. Checked codes and got 2-2-1 (O2 sensor). After the car had cooled off I cleared codes and re-started with no ill effects and the O2 sensor voltage is swinging from .3 to 1.0v. I'll have to bring to full temp to try to recreate and check O2 again. Is this an O2 sensor going bad and shoeing itself when the car is fully heated or is the cat overheating and causing the sensor to stop working properly?

Thanks for any help in advance.
--
Dirk Story








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    Rough running, O2 sensor? 900 1994

    posted by  trichard on  Wed Jun 10 23:25 CST 2009
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    last visit: Fri Oct 24 05:52 CST 2014
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    if your cat is glowing orange that is a pretty good indicator of an exhaust gas restriction in the cat causing a massive heat build up. perhaps pieces within the cat have broken off. the o2 voltage fluctuations appear normal. cats should NEVER glow orange.

    your exhaust gas flow sounds profoundly constipated. how good would you feel or move about if you were so clogged?

    i think you may/will need to remove the cat and have a look.

    the humps are the giveaway. you likely broke something off within the cat going over them.








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      Rough running, O2 sensor? 900 1994

      posted by  yrots on  Sat Jun 20 09:06 CST 2009
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      last visit: Sat Apr 12 11:19 CST 2014
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      I understand how this could create the glowing CA and cause the rough running but would the rough running be there constantly from them on as a blocked CA? Also if the O2 senesor works after it cools would I get an O2 sensor error code? My first thought was the O2 was working incorrectly and pumping too much fuel to the engine which was burning in the CA but I would expect that to be backfiring also.

      I'll have to recreate the condition and then test the O2 sensor. I'm trying to get the plug ahead of the CA loose so I can pull that to see if that corrects the back pressure if the CA is clogged.

      Florida heat and humidity makes being outside a dripping wet situation just standing around.
      --
      Dirk Story








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        Rough running, O2 sensor? 900 1994

        posted by  trichard on  Sat Jun 20 10:32 CST 2009
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        last visit: Fri Oct 24 05:52 CST 2014
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        disconnect the 3 wires from the o2 sensor where they attach at the firewall passenger side. if the car runs better then you have found the trouble. then replace the sensor

        the cat still should NOT glow orange no matter what condition the o2 sensor is in.
        orange cats invariably mean restriction and must be corrected.








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          Rough running, O2 sensor? 900 1994

          posted by  yrots on  Sun Jun 28 06:57 CST 2009
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          last visit: Sat Apr 12 11:19 CST 2014
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          I have pulled the cat but in looking into it all I see is a mesh screen on the inlet side. How do I determine blockage other that blowing air through it with a shop vac?

          The last time I tried to drive the car, I drove for approximately 15 minutes before the rough running began.

          I tried to loosen the plug ahead of the cat to see if relieving the back pressure made any difference but cannot break it loose.

          I may have to button everything back up and run until it runs rough again to try testing different things.
          --
          Dirk Story








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            Rough running, O2 sensor? 900 1994

            posted by  yrots on  Sun Jun 28 07:33 CST 2009
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            I hooked a shop vac to the exhaust end of the cat and had very good air movement thru the cat so I'm thinking there is no blockage in the cat. I'll hook everything back up and try to get the symptoms to return and pull the disconnect the O2 when it acts up to see if the rough running is a malfunctioning sensor after it heats up.
            --
            Dirk Story








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              absolutely NOT 900 1994

              posted by  trichard on  Sun Jun 28 07:48 CST 2009
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              do not disconnect any sensor with engine running. as i said specifically disconnect the 3 o2 sensor wires with the car off and then run it. the car will run better if the sensor is dead. you can also use a multimeter to measure the oscillations in the signal wire from the sensor while the car is running to see how fast they move and what the range is.








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                absolutely NOT 900 1994

                posted by  yrots on  Mon Jun 29 05:19 CST 2009
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                last visit: Sat Apr 12 11:19 CST 2014
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                With the cat off the car there was no loose material evident from shaking it. The volume of air moving through the cat from my shop vac would not lead one to believe there is a blockage as I get very good air moving through it. I did put everything back together and ran the engine until the symptoms returned (rough running) which took approximately 15 minutes at which point it was hard to keep the engine running at all. I shut off the engine and individually disconnected the O2 sensor and the MAF sensor trying to run the engine w/o each individually but the rough running continued. The measurements of the voltage fluctuations seem to indicate a problem as the fluctuations do not seem to over a wide enough range (@ 2V setting the range was .001 to .009). My leaning is toward the O2 sensor and not the cat. I also have not seen the cat overheated as I saw the very first time.
                The problem seems to be intermittent as at one point after the engine was warmed up and the problem reappeared and I was testing things, it cleared up for a couple of minutes before returning. Because of the intermittence and the need to heat up to appear and the onset of the problem after going over a speed hump, maybe I should recheck all of the electrical connections to see if it is as simple as a loose connection to a sensor or computer.
                --
                Dirk Story







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