Re: O2 Sensor

[human <human@nh.ultranet.com>]

-- [ From: human * EMC.Ver #2.5.02 ] --

>>
I've been kind of waiting to say this for a few days, and since no-one else
has I will.  O2 sensors are of course important to the overall functioning
of your car.  But what they do is mostly do some fine regulation of
pollutants by measuring oxygen in the exhaust.  They seem to be one of the
"maybe it's the..." components that we all wish it *was* when our Audis
start running cruddy.

They can be tested easily.  They are part of a feedback loop, in that their
output voltage is proportional to the ox. in the exhaust gas.  This info is
fed to the computer, which alters running params to optimise this
measurement (for the EPA not your 1/4 or 0-60...).  As a result the sensor's
output fluctuates over a small range quite steadily.  On my  83 5kt I
beleive it was 600 to 900 mV - it would take a few seconds to go back and
forth.  The optimum is 750 and the computer is always correcting and
overshooting slightly and then recorrecting.

Where are they?  Screwed into your exhaust manifold.  Down about a foot on
the pass. side of the l5 engine; but they always have this 18 inch or so
pigtail leading to a connector that is easy to reach, it usually is knocking
around by the strut tower.  Should be a green wire going to a tan plastic
connector, shoved into a black rubber boot going to the wire (black?) that
goes down to the sensor.  just pull the boot back without disconnecting the
sensor and measure with your voltmeter to ground.  If your see the small
voltage cycling back and forth, it's probably fine.  I think we looked up
the target voltage in a standard "import cars 1983" type shop manual at a
garage I worked at (as a gopher).  If it's constant and not in this range,
something's shot.  Either the sensor or the computer.  Replace the sensor
first it's cheaper.

Someone already mentioned the special socket with a slit for the wire. 
Someone else should post hints on how to do the R/R because I swear I almost
stripped the threads on my coupe when I did it.  exhaust manifiolds are
scary.

Hope this helps a little.  What's the emoticon for bleeding knuckles?

Huw Powell
human@nh.ultranet.com
>>


Well with all the recent postings about O2 sensors, now I'm wondering if I
should dig around and replace mine.  It's an ' 86 4KCSQ and has over 100,000
miles I'm sure even though the odometer says 54,000 something.  I don't know
if the previous owners replaced and sometimes the car idles rough.  Although
now I'm wondering if I have a vacuum leak somewhere, and if I did where it
would be.  Should I replace the sensor just to be safe?  It seems like the
car should get better gas mileage than it does, but then that could be the
way I drive! ;^)  TIA for the replies !

Rob
' 86 4KCSQ
' 71 AAR Cuda


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