[V8] O2 Sensor Readings
dsaad at icehouse.net
Thu Jul 5 10:51:52 EDT 2007
This is exactly the tool you need - short of an oscilloscope.
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.
> Here's one that you can mount inside the car.
It fits with 3 wires
> (+12v, signal wire on O2 sensor, and
> MikeL's V8Q was going through O2 sensors, the temp sensor was
> He wrote to the u.washington
> "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
> if you let it idle for 5 minutes.....
> BTW, This is what ruined my 02 sensor :-("
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.
>> O2 sensor is not easy to read.
To do it right, you really need an
>> A nice digital volt meter with a calibrated bar graph
>> would also work OK - as long as the response time was fast
>> problem is that the sensor is a
very high impedance device - so
up your meter affects the output. And the output is not a
>> 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
>> can only
>> tell you if you are above or
below this number.
>> If you look at the
with a o-scope, you see something like a square wave - with
>> duty cycle of the waveform indicating the mixture. A
volt meter can
>> 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
into the connector. There are metal cable holders there to keep it
>> off the
>> axle too.
>> > Can someone interpret these
>> readings for me?
>> > To
induce a lean condition, I pulled
>> the vacuum hose off the
>> > 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
>> > 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
> 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:
>> > 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"
>> from the
>> > sensor resulting in
excess fuel being dumped which
>> would explain my poor
>> > mileage (8-10 city) and flutter/miss at
on occasion. But the
>> > second run numbers look pretty
>> 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
>> > under the distributor and plugging in.
Is this OE?
>> > Thanks,
> Scott S.
> Audifans V8 mailing list
> Send posts to:
mailto:V8 at audifans.com
> Manage your list connection:
> Have an Audi V8
question? Check the Audifans Knowledgebase!
> Have a V8 answer?
... Please help others by adding to the KB ... all
More information about the V8