Oxygen Sensor questions

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maradcliff@UNLISTED.com - 26 Dec 2005 01:53 GMT

My 89 Chevy wagon with 307 engine has been using too much gas lately,
and the "check engine" light comes on every so often. While visiting
friends today, my friend has one of those diagnostic testers, so he
plugged it in. It indicated a problem with the Oxygen sensor.
He said that he heard something about a bad oxygen sensor causing the
engine to burn too much gas. Another friend said that he dont think
thats true, because the sensor only determines the vacuum advance.

Who is correct?

Also, how does a vacuum sensor work? I mean what does it do? From
what I can see, the one wire on it goes to the distributor (I think -
kind of hard to trace with all the stuff on this engine).
Having some electronics training, do these oxy sensors change in
resistance, or are they just an on + off device, or what?

Thanks

Mark

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cselby@mts.net - 26 Dec 2005 07:04 GMT

There are a whole bunch of sensors that feed to the EMC to control
fuel and spark advance. Oxygen sensor senses oxygen (not enuff fuel
or too much) in the exhaust. This determines how much fuel is sent
through the engine. The oxygen sensor is a consumable item (like
tires) that needs to be replaced periodically. Your first friend
with the tester was correct - he pulled codes that indicated a fault
in the Ox sensor circuit. This does not automatically mean the
sensor is bad - it means that there is problem in that circiut
(although my money is on the sensor ). You can unplug the connection
and the engine will run in failsafe - meaning it will set the fuel at
a predetermined 'safe ' point. This is not a great long term plan -
replace the sensor.

Since computerized engine controlers, Vacuum advance is a thing of the
past. Ignition advance is controled by the values from various
sensors which are sent to the controler that continuously sets timing.
Your second friend is off.

Pete

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Mike Romain - 26 Dec 2005 15:10 GMT

The amount of oxygen in the exhaust indicates how much fuel it used.
Too low and it tells the fuel system to pour on the gas in the mix, too
much and it tell the fuel system to lean it out.

It doesn't affect the timing, just the amount of gas burned.

If you are using too much gas, suspect a bad O2 sensor. If you also
pull codes 'saying' the sucker is dead, well..... I would believe the
codes.

It is 'not' a vacuum sensor. It senses oxygen. Most are a thermal
electric device that puts out power when the O2 is correct. They get
kinda complicated. See: http://auto.howstuffworks.com/question257.htm

A Vacuum sensor is just a switch. When the vacuum reaches a certain
point, it turns on or off.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
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> My 89 Chevy wagon with 307 engine has been using too much gas lately,
> and the "check engine" light comes on every so often. While visiting
[quoted text clipped - 15 lines]
>
> Mark

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Raymond J. Henry - 28 Dec 2005 02:43 GMT

Friend #1 is right, friend #2 is dead wrong. Keep both friends, #1 can
help you with your car, find friend #2's talents elsewhere. Just keep
him away from your car... :)

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maradcliff@UNLISTED.com - 30 Dec 2005 05:26 GMT

>Friend #1 is right, friend #2 is dead wrong. Keep both friends, #1 can
>help you with your car, find friend #2's talents elsewhere. Just keep
>him away from your car... :)

Thanks for everyone's advice on this. I should note that I should not
have used the word "vacuum" in "vacuum advance". Yes, it's electronic
advance. My mistake. It's habit to call it that after all the years
of puttering with cars.

Happy New Year to all

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