Date: Fri, 26 Nov 1999 18:04:43 -0800
Reply-To: Mark Keller <kelphoto@ISLANDNET.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mark Keller <kelphoto@ISLANDNET.COM>
Subject: Re: How does the Oxy Sensor Work/ go bad?
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Thanks Ken!
I appreciate your information about the operation of the O2.
If you don't mind I'd like to talk about this further? My main thinking is
that on some vans the "intermittent or surging power problem is related to
water in the fuel supply.
But what I don't know is how the water in the fuel would affect the ECU's
version of reality. Frankly I don't remember how non injected engines
behaved with water in the fuel, it would seem they had fuel starvation.
I felt that the presence of lot of extra oxygen in the fuel/exhaust
stream would be the result of a water in my fuel, and high humidity, raining
for hours/days as here in BC. in the intake air would further introduce more
humidity
It may be that the ECU is making the maximum correct adjustment to
compensate for water in the fuel, there is just TOO much water to deal with,
and the ECU gives up.
I felt also that there was a different path that might occur. What
happens to the timing when a high 02, i.e. water in the fuel shows up?
Does the interaction of the timing correction have interplay with the O2
sensor? Or said differently, How does the ECU determine a need to adjust
spark timing?
What I would like to see is some practical explanation for how the engine
runs on water contaminated fuel. Then I would like to be able to say that
if a van has indeed has water in the fuel, a reliable symptom would
be________.
Sincerely,
Mark Keller
91 Carat
kenneth d lewis wrote:
> 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 T-5 Coupe
>
> On Wed, 24 Nov 1999 10:43:42 -0800 Mark Keller <kelphoto@ISLANDNET.COM>
> writes:
> >Greetings,
> >
> >Can someone tell me how the Oxygen sensor actually works. Does is
> >work
> >by actually sensing oxygen in the exhaust? Or does it "correlate" by
> >providing exhaust temperature to the ECU, which then interprets the
> >Oxygen based on other inputs from the injection system.
> >
> >Does water or methanol in the fuel cause the oxygen sensor to read to
> >rich or lean?
> >
> >Does water or methanol, or other fuel additives, cause an oxygen
> >sensor
> >to fail prematurely?
> >
> >Sincerely,
> >
> >Mark Keller
> >91 Carat "Lazarus"
>
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