Multiple oxygen sensors: Some information

Discussion in 'General Motoring' started by TeGGeR®, Aug 12, 2006.

  1. TeGGeR®

    TeGGeR® Guest

    Pursuant to a recent thread on the number of oxygen sensors in the 1986 or
    1988 Honda Pelude, I asked my mechanic about this.

    It seems the reason the '88 Prelude had two O2 sensors right beside each
    other had to to do with control over emissions. It's well known that OBD-II
    systems have two sensors, one before the cat and one after, but pre-OBD-II
    engines like the '88 Prelude's have two sensors for entirely different

    OBD-II cars use the second sensor primarily as a cat efficiency tell-tale.
    When a second sensor was used in cars like the pre-OBD-II '88 Prelude, it
    meant the engine management system had divided the exhaust into two
    streams, each with just two cylinders, and was monitoring each stream
    separately. The two INNER cylinders were monitored by one sensor, and the
    two OUTER cylinders were surveilled by the other sensor.

    Two sensors meant that Honda was able to monitor and adjust mixture and
    emissions twice as efficiently as it would have been able to with just one
    sensor covering the exhaust streams from all four cylinders at once. My guy
    could not remember offhand whether Honda did this just for the carbed
    versions of the Prelude or both carb and FI models.

    Furthermore, he tells me that the very latest cars are beginning to do this
    two-cylinder splitting again, but this time each pair has its own catalytic
    converter and pair of oxygen sensors. For example, some Ford V8s have FOUR
    catalytic converters and EIGHT oxygen sensors. Can you imagine owning one
    of these once the warranty runs out?

    I'll stick to my '91, thanks.
    TeGGeR®, Aug 12, 2006
  2. TeGGeR®

    Nasty Guest

    Great report. Thanks TeGGeR.
    No kidding.
    And me wit me '00
    Nasty, Aug 12, 2006
  3. TeGGeR®

    Elle Guest

    I dunno. Might be that the improvement in fuel mileage (via
    more precise engine controls over each cylinder's air/fuel
    charge etc.) makes the extra sensors worth it.
    Elle, Aug 12, 2006
  4. Some older cars may have two sensors that operate at two ranges. Newer
    sensors combine multiple ranges in one package.

    I couldn't care less what Ford does. Even a Kia will be more advanced
    soon. Doesn't Honda tune the individual cylinders using the crankshaft
    position sensor? Or maybe not any more? My 05 HAH engine has run like
    an old beater from day one. It's not silky smooth like the 97 Civic HX
    that I had.
    Kevin McMurtrie, Aug 12, 2006
  5. TeGGeR®

    Matt Ion Guest

    I love my '87 :)
    Matt Ion, Aug 12, 2006
  6. TeGGeR®

    jim beam Guest

    no kidding!
    yes - it measures crank rotation velocity resulting from each ignition
    that's because fix or repair daily always were/will continue to be the
    cheapest pieces of garbage on the planet. and when i say "cheap", i
    mean they leave no corner left uncut in their relentless pursuit of cost
    cutting. if another manufacturer uses 4 screws to hold something down,
    they'll use 3. cast iron crank shafts? no problem! smaller bearings?
    you betcha! low-yield crumple zones /behind/ the engine to cause more
    frequent accident write-offs? and who'll rather pay a few g's to lobby
    for red rear turn signal lenses rather than incur about $3 per vehicle?
    screw the danger in modern high density high speed traffic! hmmm, i
    wonder who that might be...
    jim beam, Aug 12, 2006

  7. I'll stick with my '83. Now getting 36 mpg in mixed driving and it
    seems to run better every time I drive it...


    (The A/C is next on the list to do)
    Grumpy AuContraire, Aug 12, 2006
  8. TeGGeR®

    Matt Ion Guest

    Well at least you're not bitter..! :)
    Matt Ion, Aug 12, 2006
  9. TeGGeR®

    jim beam Guest

    just wait, one day, i'll say what i /really/ think!
    jim beam, Aug 12, 2006
  10. TeGGeR®

    TeGGeR® Guest

    Until they require replacement, at which point your fuel savings dollars
    are more then negated. There is such a thing as false economy.
    TeGGeR®, Aug 13, 2006
  11. TeGGeR®

    TeGGeR® Guest

    Ford was just my guys big example. Nissan is the other one. With emissions
    limits strangling down ever tighter, eventually every maker will be doing
    the two-cylinder split, even Honda.

    Yes, but it cannot tune the MIXTURE for individual cylinders without a
    sensor for each cylinder. If emissions limits keep going down as they are,
    one day you'll see a 4-cyl engine with 4 cats and 8 sensors. But by that
    time the electric car may render all those regulations moot.
    TeGGeR®, Aug 13, 2006
  12. TeGGeR®

    Elle Guest

    Because OEM oxygen sensors are so darned cheap for the early
    90s Civics (for one), I have my doubts. At least at they're mighty cheap.

    I know O2 sensor design is different and may not be
    consistent with OBD-II yada, but putting that aside for the
    moment, ISTM the engineering might be cost effective.

    You could be right. I just don't like throwing out something
    as "definitely wrong" without numbers and/or serious
    evidence. It's not entirely an academic subject either,
    ISTM, in these days of high gas prices.
    Elle, Aug 13, 2006
  13. TeGGeR®

    Matt Ion Guest

    By that time, I better have my freakin' FLYING car that Popular Mechanics
    promised me 30 years ago :p
    Matt Ion, Aug 13, 2006
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