Date: Mon, 5 Feb 2001 14:50:22 -0500
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: O2 Sensor voltage
In-Reply-To: <3A7ED878.1560613A@islandnet.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed
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!
>and upper volt output of the O2 sensor, in closed loop of course, are
>obtainable. From my testing on my van the average low was .3 and high
>..8.
That was about as far as I could get the signal to travel while hooked to
the ECU and scope.
>I've found that it is easier for me adjust my fuel injection mixture by
>disconnect the O2 sensor to put the ECU in open loop and then monitor
>the O2 readings while driving. Using this method I can adjust spring
>tension , or in my case fuel pressure or wiper arm position, so that the
>ECU maintains the fuel mixture around a target voltage. I target at .7
>volts. Then I reconnect my O2 sensor and consider that part of the
>injection system adjusted.
Makes sense. Playing with it just now (my AFM cover just happens to be a
snug sliding fit :) I found that the difference between pegged low and
pegged high (at say 3000 rpm) was less than one click of the spring
adjustment. Mine had been set two clicks lean from that point. I wasn't
able to get a reading higher than 0.8 volts even by moving the air flap
open until the engine died from (I presume) overrich.
david
David Beierl - Providence, RI
http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"
