[V8] O2 Sensor Readings
dsaad at icehouse.net
Tue Jul 3 18:58:08 EDT 2007
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 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
> 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
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 -
> 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
> 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" signal
> 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
> 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?
> Scott S.
> Audifans V8
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