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02 sensor issue really confusing me.... 700

Morning and thanksgiving (I am thankfull for BB)

92 745 T

My check engline light comes on.
I get O2 code from the LED.
I check voltage at O2 black lead while still plugged in and with car warm and running.
No voltage swings.
I install new O2 sensor.
I clear code.
Things look good for a test drive.
No, the CEL is back on O2 code is given.
No voltage swing!

This is the second O2 sensor I put on (I used the mustang one <$$)

Shouldn't a sensor create voltage regarless of what it is connected to? It is self generating - so the fault is not elsewhere?


What is the dealeeoo?

Happy Thanks








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    02 sensor issue really confusing me.... 700

    Do the pinch (gently) the fuel return line test. Pinching it raises the fuel pressure making the mixture richer resulting in an O2 sensor change. Releasing the pinch makes it go the other way. Personally I won't use a generic (V-8 Mustang) sensor after my 3 week nightmare to discover the rolled joint of the sensor head leaking causing a rich condition. NGK or Bosch only. Yeah, yeah I know the heads are all the same but how the attach the head is different.

    ian








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    02 sensor issue really confusing me.... 700

    Howdy. Any luck yet?

    I prefer analog meters. No crappy "compensation" or auto-ranging to interfere with my raw data and continuously moving needle.

    If your voltage is not swinging on a new sensor, you've got a problem with the mixture.
    When I test my O2 sensors, it's merely for "does the voltage swing? and how quickly?". I test with the car running. The voltage should swing from just above 0V to just below 1V. You could call it a quick and dirty test, but it's testing the essentials and not fussing over the unimportant details.
    Positive lead on the O2 sensor output, Negative(black) lead grounded somewhere I've scratched a fresh ground path. Rev the engine a couple times.
    I usually goose the throttle a couple times, then hold the engine at 1500 and let go of the throttle. Each time the engine speed changes, you should see the sensor swing one way for a brief time, then return to a steady cycle somewhere between 0 and 1V.

    A new O2 sensor is not likely to be bad off the shelf, even if it's a mustang sensor (Can you explain that more). Replace your plugs with NGK Coppers (or something else if you prefer), Pull the vacuum line from your
    FPR and check for liquid gasoline. Try testing the O2 sensor again.

    By the way, are you checking the O2 sensor output with the O2 sensor connecter to the harness, or with the sensor wire disconnected? Do you get different results if you try with the wire plugged and unplugged?
    --
    1990 740 Turbo, on its way to stock specs, maybe beyond








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      02 sensor issue really confusing me.... 700

      not fixed yet. It is running super lean.

      Maybe short in 02 sensor lead...
      Bad ECU grounds...
      Bad ECU...

      I used a Mustang O2 sensor per the FAQ how to links.

      The 02 sensor works (bench tested per http://mr2.com/TEXT/O2_Sensor.html) but is giving 0.04v in closed loop when on the car attached to harness and running and warm.

      see what happens today









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        02 sensor issue really confusing me.... 700

        Do you get the same voltage with the sensor connected to the wiring harness as with it disconnected?
        --
        1990 740 Turbo, on its way to stock specs, maybe beyond








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          02 sensor issue really confusing me.... 700

          with car warmed up and running

          measuring V across the O2 lead and ground:

          02 lead connected I get V = 0.012

          With it disconnected V = 0.8ish

          The Voltage of the discoonected lead climbed as the car warmed up

          As it was warming with 2000 rpm it read 0.8ish but 0.2 v at idle

          Now with engine fully warm it always reads 0.8ish V with lead disconnected








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            02 sensor issue really confusing me.... 700

            Bingo. Sounds like you've got a problem with the wiring from the O2 sensor to the ECU. Potentially there's an issue with the ECU, but let's not go there yet.

            Does anyone know the pinout from the ECU to the O2 sensor?

            I suppose you can test (engine off) for resistance between the O2 sensor connector in the wiring harness (not the lead) and the ground. It should be anything but 0.


            --
            1990 740 Turbo, on its way to stock specs, maybe beyond








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              02 sensor issue really confusing me.... 700

              that was it!

              all fixed!








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                02 sensor issue really confusing me.... 700

                Wait! What was it? Bad wiring shorting out somewhere?
                --
                1990 740 Turbo, on its way to stock specs, maybe beyond








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                  02 sensor issue really confusing me.... 700

                  yes, my O2 sensor lead has shielding around it. The shielding is to ground and it was shorting to the O2 sensor + lead. I cut out the bad section and respliced...








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                    02 sensor issue really confusing me.... 700

                    Cool. Thanks for posting back what you found. It might help someone with the same problem in the future, but not if you don't post the final fix ;)
                    --
                    1990 740 Turbo, on its way to stock specs, maybe beyond








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    02 sensor issue really confusing me.... 700

    What is the voltage reading? It might be that you aren't seeing swings because you are pegged at rich or lean. The O2 sensor just tells you what it "sees" in the exhaust gas. If the oxygen level in the exhaust gas is constant, the reading will be too. With a failed fuel pressure regulator (for example) you would see rich running all the time, so the O2 sensor will reflect this bias.

    To me this probably means that the O2 sensor code is a symptom rather than the cause of your problem.

    I'd be on the look-out for things like a failed fuel pressure regulator, a bad coolant temperature sensor or a vacuum leak. Any issues with how the car runs?

    Good luck!








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      02 sensor issue really confusing me.... 700

      The voltage is really low = 0.014v ish



      A little hard to start but will take after a little pedel push,

      Needs to rev it up then back to idle it is ok.

      Feels like a little missing but goes away with high reving.

      I know I have to get new plugs b/c the platinum bosch are resisance plugs and so are the wires. I need to get copper plugs so I am not double dipping on the resistances.

      good leads here - thanks








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        02 sensor issue really confusing me.... 700

        Are you sure you aren't off by a decimal place? The normal range for the 02 sensor is 0.15-0.85 VDC.

        I would definitely ditch the platinum plugs and see if it runs better. Then I'd move on to some further diagnostics.

        Good luck!








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    02 sensor issue really confusing me.... 700

    What voltage do you read?
    What voltmeter are you using? A high-impedance DVM is necessary.








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      02 sensor issue really confusing me.... 700

      reading steady low of approx 0.014v

      I believe the DMM is of right quality. How can I tell the impedence limits of the DMM?

      It is a good quality one from Radio Shack - it has given me swing readings before.

      I do put the setting to DC volts at 4vmax reading. One lead to COM and other to Volts

      thanks








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        02 sensor issue really confusing me.... 700

        the reading is low. I disconnected the lead and was measuring approx 0.045v (yes 0.045V)

        This is really weird

        I am going to bench test the sensor per

        http://mr2.com/TEXT/O2_Sensor.html

        ugg







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