For us as owners to look at a closed loop O2 sensor reading and then
believe we have "checked" the operation fuel injection system including
of the AFM spring tension or wiper arm is not valid.  This is the point
I'm trying to make.

We must check the system open loop first..   If you test your system
open loop first and have a target value of say .5-.6 volts, then go
closed loop and drive the vehicle you will have duplicated my
experiment, and then we can see if the closed loop cycle behaves as
expected.

Sincerely,

Mark Keller
91 Carat

Date:    Mon, 5 Feb 2001 14:50:22 -0500
From:    David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: O2 Sensor voltage

At 11:44 AM 2/5/2001, Mark Keller wrote:

>As to the notion that the ECU adds fuel pulse until the other trigger
>point is reached, I don't believe this is the case. Darrel would
>probably be a better source when he returns.  In my observations it
>appears that the ECU has a sampling interval. In other words when a
>trigger point is reach, an injector pulse adjustment is made and then
an
>interval before another adjustment is made.

Ok, I just looked at the FI book (which says one adjustment cycle per
1-2
seconds at idle, several per second at speed) and then went out (in a
snowstorm, I must be crazy!) to put a scope on it.  Results were
variable
timing at idle but usually about 1.5 seconds/cycle (going rich -- going
lean -- going rich again) , and about four to six cycles per second at
3000+ rpm.  Voltage extremes were about 0.2 and 0.8 volts, hooked to a
scope with 10Mohm/13pf impedance and grounding to the common point on
the
left head.  At idle speeds the transitions took an appreciable fraction
of
the cycle; at high speed the waveform was pretty square and with roughly

equal duty cycle.  This is a 1.9l (sensor in the collector pipe) with a
Bosch Vanagon-specific one-wire sensor with probably 15,000 miles on
it.  I
didn't try to correlate injector timing with lambda sensor readings, too

much snow dropping down my neck!