[V8] O2 Sensor Readings

Thu Jul 5 10:51:52 EDT 2007

This is exactly the tool you need - short of an oscilloscope.
There
are also volt meters with similar functions (bar graphs) built in, but
they will set you back a good $300 for a nice Fluke or equivalent. The
cheapo meters are not worth much in this application.

Dave

> Here's one that you can mount inside the car.  
It fits with 3 wires
> (+12v, signal wire on O2 sensor, and
Ground).
> 
> http://tinyurl.com/39bfnd
> 
> MikeL's V8Q was going through O2 sensors, the temp sensor was
the
> culprit.
> 
> He wrote to the u.washington
list:
> 
> "It's easy to test.  let car sit
overnight, then measure the resistance
> between the 2 pins on the
sensor.  Should be between 1.5 to 3 ohms.
> 
> Mine was at
4.5 and it made the car run so rich that you got a huge black
>
cloud when you stepped on it.  As well as a pile of soot under the
> tailpipe
> if you let it idle for 5 minutes.....
>

> BTW,  This is what ruined my 02 sensor :-("
> 
> BCNU,
> http://www.geocities.com/cobramsri/
> We
come into the world naked, screaming and covered in blood. Why should
> the fun end there?
> 
> "d saad"
<dsaad at icehouse.net> writes:
>>
>>
>> I am not sure you can deduce much at all from this Scott.
>>
>> The
>> O2 sensor is not easy to read.
To do it right, you really need an
>> oscilloscope.
>> A nice digital volt meter with a calibrated bar graph
>> would also work OK - as long as the response time was fast
enough.
>> The
>> problem is that the sensor is a
very high impedance device - so
>> just
>> hooking
up your meter affects the output. And the output is not a
>>
steady
>> state voltage - unless you are at extreme rich or
lean condition. It
>> is a
>> non-linear device with
the usable range being a very narrow band
>> around a
>> air/fuel mixture of 14.7. For most practical purposes, the
sensor
>> can only
>> tell you if you are above or
below this number.
>> If you look at the
>> signal
with a o-scope, you see something like a square wave - with
>>
the
>> duty cycle of the waveform indicating the mixture. A
volt meter can
>> give
>> you a rough idea of the
duty cycle - because it averages the
>> readings, but
>> it is a very rough indication.
>>
>>
>> And - no - your O2 sensor
>> wiring does not sound 
OEM. Mine just snakes over the axle and
>> right
>>
into the connector. There are metal cable holders there to keep it
>> off the
>> axle too.
>>
>>
Dave
>>
>> > Can someone interpret these
>> readings for me?
>> >
>> > To
induce a lean condition, I pulled
>> the vacuum hose off the
FPR*.  To
>> > induce a rich condition, I
>>
plugged the FPR's vacuum hose and/or sprayed
>> > some carb
&
>> choke cleaner into the hose (it was the only thing
flammable
>> > I
>> had, besides electronic
contact cleaner.. which I sprayed too).
>> >
>>
>> > First run, cold engine
>> >
Idle:  0.01 - 0.03 VDC
>> > 1000 rpm:   0.02 - 0. 03 VDC
>> > 2000 rpm:   0.23 - 0.28
>> VDC
>>
> 3000 rpm:   0.29 - 0.35 VDC
>> > 2500 Lean:  0.22 -
>> 0.25 VDC*
>> > 2500 Rich:   0.23 - 0.25 VDC
>> >
>> >
>> Second run, hot engine
>> > Idle:  0.4 - 0.5 VDC
>> > Idle Lean:
>>  Very sluggish drop from 0.5 to 0.19* (sluggish meaning it
>> > took
>> 3-6 seconds)
>> > 2500
rpm:  0.51 - 0.52
>> > 2500 Lean:
>> 0.52*
>> > 2500 Rich: Sluggish rise to 0.66
>> >
>> > * -
>> in the end, the lean condition from the
vacuum hose could have been
>> > offset by the excess fuel
dumped by the FPR
>> >
>> >
>>
After the first run, I thought I'd nailed it.  A "lean"
signal
>> from the
>> > sensor resulting in
excess fuel being dumped which
>> would explain my poor
>> > mileage (8-10 city) and flutter/miss at
>> idle
on occasion.  But the
>> > second run numbers look pretty
good.
>> The lean condition at idle did go
>> >
down to the correct numbers,
>> albeit sluggish.  The Lean
2500rpm can't be
>> > trusted, IMO.
>> >
>> > The only thing pointing to a bad sensor is the sluggish
>> changes.  Should
>> > I go ahead and replace the
sensor or wait until
>> my second-hand laptop
>>
> arrives for VAGCOM?  Sensor replacement
>> was going to be
a Ford but I
>> > haven't decided on 3 or 4 wire.  Is
>> 4 wire more trouble than its worth?
>> >
>> > One last
>> question:  How long is the sensor
wiring?  Mine comes up from
>> >
>> the sensor,
zip-tied to the transmission tube, then it loops to the
>> >
shock tower (zip-tied to the brake line brackets) before going
>> back
>> > under the distributor and plugging in. 
Is this OE?
>> >
>> > Thanks,
>>
> Scott S.
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