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bad O2 sensor?? 700

uid 48709's pic
posted by  shegarty on  Tue Sep 6 06:18 CST 2011
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last visit: Mon Dec 19 08:19 CST 2011
[RELATED]

hi all - the CEL is on in my '90 740 2.3T - fault codes in position 2 read 2-2-1 and 2-3-1, fuel trim too lean or rich at part load - she has been running like this for several months now (two kids, full time job and home renos - no time for the car!) with no running issues, starts, idles and runs great and gets the same gas mileage (25-29 mpg) as she always has

my thought is that there is probably faulty connections/wiring somewhere that is generating the trouble code - the problem is that she is due for an emissions test here in ontario next month and most places won't test it if the CEL is on - should i start replacing parts, O2 sensor?? AMM?? fuel pressure regulator?? any insights are always appreciated :)
--
90 740T wagon, 94 850 T5 wagon








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    bad O2 sensor?? 700

    uid 48709's pic
    posted by  shegarty on  Tue Sep 20 12:29 CST 2011
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    last visit: Mon Dec 19 08:19 CST 2011
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    checked AMM against reference from FAQ - checked fine
    replaced O2 sensor - CEL kept triggering
    hard reset on ECU - pulled no.1 fuse (ECU & fuel pump) - no more CEL!!!
    --
    90 740T wagon, 94 850 T5 wagon








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    bad O2 sensor?? 700

    posted by  Will740turbo on  Wed Sep 7 13:50 CST 2011
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    last visit: Wed Oct 22 16:09 CST 2014
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    I'd start by checking the voltage your O2 sensor is putting out with an analog multimeter. See if it sweeps back and forth and nearly hits 0v and 1v.

    Then I'd reset the codes and check for vacuum leaks. I'd also check the O2 sensor output again to see if it's sweeping the full range of 0.1 to 0.9V or is stuck in one area.

    25-29mpg in a turbo?? A manual? That's amazing mileage!

    Good Luck!







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      bad O2 sensor?? 700

      uid 48709's pic
      posted by  shegarty on  Thu Sep 8 06:00 CST 2011
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      last visit: Mon Dec 19 08:19 CST 2011
      [RELATED]

      thanks for the tip - i will get my hands on an analog meter and test it this weekend - excuse the obvious but i am assuming that i am testing it while running?? which wires (two white, one black) should i be testing the voltage on??

      25-29mpg is the ususal ballpark for the old girl - better in the warmer weather - she is a automatic too - i drive mostly highway back and forth to work everyday but even in the city she doesn't usually drop below 22-23 - and she has over 350k km on her now :) hopefully i can get this sorted and keep her roadworthy without too much expense
      --
      90 740T wagon, 94 850 T5 wagon








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        Analog meter generally NOT recommended for O2 sensor testing 700

        uid 18083's pic
        posted by  lucid on  Thu Sep 8 06:42 CST 2011
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        last visit: Fri Oct 24 12:31 CST 2014
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        From the 700/900 FAQ section on Oxygen sensor testing:

        "You need a digital voltmeter with an impedance of at least 10 megohms to prevent damage to the ECU."

        More O2 sensor testing info HERE in the 700/900 FAQ.


        --
        Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.







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