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Both O2 Sensors - Replaced (Initial Reving?)

Discussion in '80-Series Tech' started by HuletCruiser, Feb 27, 2007.

  1. HuletCruiser

    HuletCruiser

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    Hello Folks,

    Replaced my two oxygen sensor today. Had the CEL light lit. Purchased the front and rear at Sparkplugs.com and had them in about 4 days UPS. Had been working on my rusty nuts and finallly got them off (some I had to break off) Purchased a die and got the threads back again and got the stainless nuts to replace the original ones.

    Intersting thing and I wanted to ask if this has happened to anyone else. I have not read that it has??? After replacing both O2 Sensors and reconnecting the battery cable, I started her up and the engine, all by itself, reved to about 2500 rpm and then down to about 1000 then back up to about 2500 rpm and then back down again. It did this about 4 or 5 times with my foot off the gas....then it leveled about at about 1100 rpms. After running it a bit it leveled off at around 550 rpms...

    Just wonder if this is a normal cycle when replacing O2 sensors on this FZJ-80 (1997) ?

    Thanks!

    Jason Hulet
    1997 FZJ-80, Factory Locked, Black/Gray
     
  2. Nemo

    Nemo

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    This is normal I suppose. That is what happens with the OBDII engines. 97. I get the same behavior until I restart the engine a good 4-5 times. 550rpm seems a little low for it to settle at however?
     
  3. cam75w/ls1

    cam75w/ls1

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    It'll relearn itself after a drive cycle. Computers are stupid until a closed loop status has been obtained. Meaning fully warmed up and run under different load conditions.
     
  4. DanKunz

    DanKunz SILVER Star

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    Mine did the same thing, it went away.
     
  5. Beowulf

    Beowulf

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    Jason,
    This has been mentioned about a hundred times. When the battery is disconnected, the main engine ECM loses it's acquired fuel mapping and it has to re-learn. It will do this whether you replace the O2 sensors or not, though new O2 sensors may exacerbate the learning curve.

    -B-
     
  6. HuletCruiser

    HuletCruiser

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    Thank you for the replys..

    Thanks Guys for the replies. I figured the same, just didn't remember reading about the reving part...

    :)
     
  7. GeoRoss

    GeoRoss

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    This is funny you bring this up as I thought my ECU was stupid. After doing EGR work and fuel filter replacement I noticed that my ECU took alot of driving to get back to normal. It took a dozen or more start cycles for the idle to be normal after 'fixing' my code 71. The fuel filter took 5 or 6 starts cycles to relearn.

    Undoing the battery for other work only requires a couple of start cycles for the idle to return to normal.


    I guess it hadn't bothered me enough to worry me into thinking about it.

    :cheers: