Date:         Wed, 12 Jan 2000 06:35:48 EST
Reply-To:     kenneth d lewis <kdlewis@JUNO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         kenneth d lewis <kdlewis@JUNO.COM>
Subject:      Re: (LONG) Surging Idle fixed! / Surging O2 sensor readings
Comments: To: glmce@HOTMAIL.COM

Gary;
        The surging could be due to one of three things. All involving
the throttle body adjustments. The idle position sensor, idle stop and
idle adjustment. The O2 sensor portion is working perfectly!!!!! Heres
why.

Diagnosing Oxygen Sensors:

The oxygen sensor is really a simple device : It tells the engine
computer how much O2 (oxygen) is left in the exhaust . With this
information the computer can determine the best air/fuel ratio ;
stoichiometry.

When the O2 sensor detects too little oxygen in the exhaust it tells the
computer the engine is running rich (please send less fuel).On the other
hand too much O2 means a lean mixture (please send more fuel).

The O2 sensor kind of acts like a fuel cell(a battery is a good analogy).
A voltage is produced (1 to 1.5 volts) when there is a difference of
oxygen levels between the inside of the sensor(the environment air) and
the outside of the sensor sitting in the exhaust stream . This indicates
a rich condition or to little O2.When there is O2 in the exhaust (lean),
the inside and outside of the sensor has less O2 differences and the
voltage output drops to zero.

BUT the sensor must reach operating temperature to work(real hot) i.e.
the computer ignores any input from sensors on a cold engine. This is
known as "open loop operation",the computer wings it.After the sensor
heats up the computer goes into "closed loop operation".The sensor
detects a lean mixture then the computer allows more fuel from the
injectors. This produces a rich mixture,sensor voltage drops,computer
leans out the mixture.An endless cycle. In other words the mixture never
stabalizes at perfect but continuously toggles around it.

If you have a good voltmeter you should see this voltage swing from a
fully heated operational sensor.

You can test your system with a 1.5 volt flashlight battery. Disconnect
the sensor lead. This is easiest deduce with a single wire sensor. Three
wire sensors have two wires for a heater, DONT mess with these.Connect
the negative side of the battery to chassis ground. touch the sensor wire
going to the computer to the positive side of the battery.This fools the
computer in thinking there is a rich mixture present. It attempts to
correct by leaning out the mixture ,hopefully making the RPM's drop.The
output of the sensor should drop also.

On the other hand if you ground the sensor lead going to the computer it
thinks the there is a lean mixture and attempts to compensate by send
more fuel hence the engine SHOULD surge. At this time the output of the
sensor should climb.



Drive Safely & Good Luck
Ken Lewis<Kernersville,NC>86 VW crewcab;60 356B Coupe
For Sale: 61 AustinHealey Sprite(not Bugeye);Daily driver $2500

On Wed, 12 Jan 2000 00:55:38 EST Gary McEachern <glmce@HOTMAIL.COM>
writes:
>Hello
>I'm still having a problem with the FI..... the voltage starts to ramp
up and down from 0 to 0.8V every few seconds.

________________________________________________________________
YOU'RE PAYING TOO MUCH FOR THE INTERNET!
Juno now offers FREE Internet Access!
Try it today - there's no risk!  For your FREE software, visit:
http://dl.www.juno.com/get/tagh.