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Date:         Wed, 12 Jan 2000 08:08:39 -0600
Reply-To:     Darrell Boehler <midwesty@MIDWEST.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Darrell Boehler <midwesty@MIDWEST.NET>
Subject:      Re: (LONG) Surging Idle fixed! / Surging O2 sensor readings
Comments: To: Gary McEachern <glmce@HOTMAIL.COM>
Content-Type: text/plain; charset="iso-8859-1"

Hi Gary, It is normal for the o2 voltage to bounce above and below 0.5 volts. Usually the bounce is more in the 0.2 - 0.7 volt area. Additionally it is difficult for a digital volt meter to lock onto a o2 voltage. The meter samples the voltage every second or so and displays the voltage at the time of the sample. I assume you are getting voltage readings all over the 0.2 to 0.8 volt area. Since it is normal for the mixture to go from a slightly rich to a slightly lean situation. Your vans closed loop mixture appears to be pretty much normal. Our digifants assume any voltage from the o2 sensor is correct. If you have a bad ground, bad o2 wire, bad sensor it can really screw things up. The ecu will attempt to vary the mixture to get the ideal 14.7 to 1 air fuel ratio by putting blind faith in the o2 voltage. Newer systems have smarter ecus and multiple o2 sensors. They turn on the check engine light and keep on going. The digifant is a good system when all is proper, it will do a great job of engine management. An old o2 sensor will take longer to transition form rich to lean. There is no easy way to test it other than replace it or hook up your van to an exhaust sniffer. Another indication is an old sensor will have fewer bounces from plus to minus per minute. I quote bosch / bentley bible on fuel management 3 - 23 " The oscillation is so fine (about 0.1 percent change in the air fuel ratio) that it is not noticed in engine performance. At idle the cycle can take 1-2 seconds. At cruising speed the cycle may happen several times a second." So when your system goes through a transition the air / fuel ratio is varying from 14.715 - 14.725. 14.72 being the perfect mixture for power and clean air.

Darrell Boehler

----- Original Message ----- From: Gary McEachern <glmce@HOTMAIL.COM> To: <vanagon@GERRY.VANAGON.COM> Sent: Tuesday, January 11, 2000 11:55 PM Subject: (LONG) Surging Idle fixed! / Surging O2 sensor readings

> Hello > I'm still having a problem with the FI in my new '87 weekender. When I first > start the van the O2 voltage starts around 0.45V and slowly climbs for about > 3-5 minutes till it reaches approx 0.8V. Once it exceeds +0.8V the voltage > starts to ramp up and down from 0 to 0.8V every few seconds.


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