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O2 Sensor Readings 85 Caprice



 
 
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  #1  
Old March 7th 05, 09:46 PM
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Default O2 Sensor Readings 85 Caprice

Hi,

I just tested the O2 sensor on my 85 Chevy Caprice. It is the
original sensor, with 368K on it, so I wasn't expecting it to be too
great at this point. I used a digital voltmeter on it by disconnecting
the pigtail, letting the car idle, and checking the voltage from the
O2 sensor's pigtail connector to a ground (the brake master cylinder).
The reading fluctuated between .01 volts and .09 volts. In other
words, it never got over .1 (one tenth) of a volt.

The engine was fully warmed up during the test. I drove the car
with the O2 sensor disconnected, and it performed the same as ever
(OK). The check engine light did not come on.

Are these low voltage readings consistent with an O2 sensor that is
worn out ? I'm sure it could use replacing, I just want to know if
these low readings are right, or there is something wrong with the
voltmeter.

Can I expect better performance / gas mileage if I replace the O2
sensor? I get 18 mpg right now on back roads back and forth to work,
which seems pretty decent for an old 305 carbed V8.

To those who replied to my previous post about the O2 sensor,
thanks. I am posting again because I now have the voltmeter test
readings.


Thanks

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  #2  
Old March 7th 05, 10:23 PM
Lawrence Glickman
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On 7 Mar 2005 12:46:13 -0800, "
> wrote:

>Hi,
>
> I just tested the O2 sensor on my 85 Chevy Caprice. It is the
>original sensor, with 368K on it, so I wasn't expecting it to be too
>great at this point. I used a digital voltmeter on it by disconnecting
>the pigtail, letting the car idle, and checking the voltage from the
>O2 sensor's pigtail connector to a ground (the brake master cylinder).
> The reading fluctuated between .01 volts and .09 volts. In other
>words, it never got over .1 (one tenth) of a volt.


Well then, it's dead.

>
> The engine was fully warmed up during the test. I drove the car
>with the O2 sensor disconnected, and it performed the same as ever
>(OK). The check engine light did not come on.


I wonder if it burned out a long time ago. Does it illuminate for a
bit when you turn the key to ON? If it had been constantly ON for the
best part of the last 20 years, I would expect the light to be as dead
as the O2 sensors by now.

>
> Are these low voltage readings consistent with an O2 sensor that is
>worn out ?


Worn out, as in these tires haven't just lost their tread, their down
to the hubcaps now.

> I'm sure it could use replacing, I just want to know if
>these low readings are right, or there is something wrong with the
>voltmeter.


I'm going to give the benefit of the doubt to the voltmeter. That
isn't 20 years old.

> Can I expect better performance / gas mileage if I replace the O2
>sensor? I get 18 mpg right now on back roads back and forth to work,
>which seems pretty decent for an old 305 carbed V8.


Who knows what else is FUBAR on that car by now? You could replace
the O2 sensors, but would that guarantee any improvement? It's a
gamble on a car that old with that many miles. If you have money to
burn, by all means, replace them. I wouldn't, as your gas mileage
seems to be acceptable to you. Compare that with the cost of
replacement. We don't even know if your engine computer works any
more at this point, if there even is one, presuming there is.

I wouldn't put any more money into a 20 year old car than was
necessary to keep it legal and moving. You have those attributes
already, so why the sudden interest in these sensors?

> To those who replied to my previous post about the O2 sensor,
>thanks. I am posting again because I now have the voltmeter test
>readings.
>
>
>Thanks


  #4  
Old March 8th 05, 01:51 AM
aarcuda69062
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In article
. com>,
" > wrote:

> Hi,
>
> I just tested the O2 sensor on my 85 Chevy Caprice. It is the
> original sensor, with 368K on it, so I wasn't expecting it to be too
> great at this point. I used a digital voltmeter on it by disconnecting
> the pigtail, letting the car idle, and checking the voltage from the
> O2 sensor's pigtail connector to a ground (the brake master cylinder).
> The reading fluctuated between .01 volts and .09 volts. In other
> words, it never got over .1 (one tenth) of a volt.


The master cylinder is a lousy place to try to obtain a ground.
Try connecting directly to battery negative.
..01-.09 volts could indicate a bad ground for the meter, a
shorted O2 sensor or an extremely lean exhaust condition.
The lean exhaust could be from an air pump that is dumping on top
of the O2 thru the manifold ports, it could be from broken
metering rod springs in the carburetor, a plugged fuel filter,
misadjusted carburetor settings, etc.
The way to tell if the O2 is dead is to flood the engine with
fuel creating a known rich condition and watching the O2 voltage
for the corresponding response, propane works well for this.

> The engine was fully warmed up during the test. I drove the car
> with the O2 sensor disconnected, and it performed the same as ever
> (OK). The check engine light did not come on.


It should have. Are you certain that it even works?

> Are these low voltage readings consistent with an O2 sensor that is
> worn out ? I'm sure it could use replacing, I just want to know if
> these low readings are right, or there is something wrong with the
> voltmeter.


As mentioned above, it could be how you connected the volt meter
ground, or it could be a false condition that has driven the
voltage low.
There is more to testing than just hooking a meter to a circuit,
one really needs to understand the dynamics of what they're
looking at.

> Can I expect better performance / gas mileage if I replace the O2
> sensor? I get 18 mpg right now on back roads back and forth to work,
> which seems pretty decent for an old 305 carbed V8.


Not bad considering how finicky that system is.
  #5  
Old March 8th 05, 01:08 PM
pater
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The only thing you were reading was a small fluctuation of voltage in
the meter. If you disconnected the sensor then hooked the meter to the
o2 sensor not connected to the system, you may as well hooked it to the
fender because you aren't reading anything. In order to get the reading
the sensor has to be hooked up & either jumped into or read from a
scanner. Try again. Also if you got no response from the ecm & no
difference by disconnecting it you may have other issues. Was there a
problem to begin with????

  #6  
Old March 8th 05, 03:27 PM
Mike Romain
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A working O2 sensor produces it's own voltage except for a couple
strange types so he tested it the way my Jeep book says is correct.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's.

pater wrote:
>
> The only thing you were reading was a small fluctuation of voltage in
> the meter. If you disconnected the sensor then hooked the meter to the
> o2 sensor not connected to the system, you may as well hooked it to the
> fender because you aren't reading anything. In order to get the reading
> the sensor has to be hooked up & either jumped into or read from a
> scanner. Try again. Also if you got no response from the ecm & no
> difference by disconnecting it you may have other issues. Was there a
> problem to begin with????

  #7  
Old March 9th 05, 02:19 AM
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Default

Thanks for the replies.

Does anyone have some input into why the check engine light did not
come on when I drove the car with the O2 sensor disconnected? The CEL
does light up when I turn the ignition to "on" before starting , so
the bulb still works.

  #8  
Old March 9th 05, 02:45 AM
aarcuda69062
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In article
.com>,
" > wrote:

> Thanks for the replies.
>
> Does anyone have some input into why the check engine light did not
> come on when I drove the car with the O2 sensor disconnected? The CEL
> does light up when I turn the ignition to "on" before starting , so
> the bulb still works.


You can have a trouble code stored without the check engine light
illuminating. Did you actually check to see if there are any
trouble codes stored?
  #9  
Old March 9th 05, 02:40 PM
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>
> You can have a trouble code stored without the check engine light
> illuminating. Did you actually check to see if there are any
> trouble codes stored?



cuda,

No, I haven't checked for codes yet. I need to figure out what
contacts to jumper with the paper clip first. One thing I noticed is
that the CEL flashes once when I turn the key to "on". The other lights
don't do that.

User

  #10  
Old March 9th 05, 03:02 PM
aarcuda69062
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Default

In article
.com>,
" > wrote:

> >
> > You can have a trouble code stored without the check engine light
> > illuminating. Did you actually check to see if there are any
> > trouble codes stored?

>
>
> cuda,
>
> No, I haven't checked for codes yet. I need to figure out what
> contacts to jumper with the paper clip first. One thing I noticed is
> that the CEL flashes once when I turn the key to "on". The other lights
> don't do that.
>
> User


Jumper pins "A" and "B" as shown here;

http://www.obd-codes.com/faq/read-gm...codes-free.php
 




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