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Re: Dangling Wires



>>Listers- In late Dec while replacing a CV boot, I noticed two unconnected
>>plugs on the drivers side inside the engine compartment. Joe Y. thought they
>>might be associated with the brake sensors. After further inspection I
>>concluded they were test connectors for the tranny, but promised to update
>>you if this was a bad call. Well I traced the wires and they went to the O2
>>sensor in the exhaust system. After much searching, I located the mating
>>jacks on the engine under the distributor/cruise control bellows. After
>>reconecting the car seems to have a bit more pep, and idles 150rpm lower. I
>>have been runing without an O2 sensor for many months. Can anyone explain
>>how this was possible? American cars won"t even start with the O2 sensor
>>disconnected.


>Most cars will run without an O2 sensor....they all run that way (open
>loop) until the sensor gets warm enough to send a signal.  That's one
>reason why most O2 sensors are heated...to get them up to temp and working
>sooner.  Without a signal from the O2 sensor you were running a default
>map, which is non-optimized...when you put the O2 sensor back in it could
>finally control mixture real-time and provide a better idle and power.

>I'd check the sensor to see if it was disconnected because it was acting
>up...if it's original w/more than 60k miles I'd just replace it.  V8's are
>finicky about the O2 sensor; sometimes they only last 30k miles.  You'll
>notice a surging in acceleration as a first sign of problems.  I'd also
>worry somewhat about the cat getting plugged if it was run a long time w/o
>the O2 sensor.

>By the way, did you pull the codes?  You should have had an error code set
>when the ECU determined that it should be getting a signal from the O2
>sensor and wasn't getting one............SLM

Well, I'd like to add a bit to this...

The O2 sensor is nothing more than a voltage generator. The ECM does _not_
have the ability to verify the sensor's temperature or accuracy. Closed loop
operation is determined by coolant temp. Once coolant temperature rises beyond
a predetermined point (usually about 170 degrees f), the ECM then uses the
O2's output voltage in it's determination of proper fuel mixture.

If the sensor is disconnected (or dead for that matter), the ECM will see zero
volts from the O2 circuit. This is registered as a lean condition, and the ECM
will respond by increasing fuel. This is the reason you should verify catalyst
function, as an overly rich condition can damage it.

Oxygen sensors do rely on sufficient heat in order to function properly. They
do  have a tendency to fail. The heating element used on sensors is there to
maintain and stabilize to operating temps. Many turbo equipped vehicles use
heated elements since the turbo eats so much temperature. The heating elements
will also increase a sensor's longevity.

I posted several weeks ago regarding 'in field' testing of oxygen sensors. If
you want me to re-up it, let me know.

Just my 2
Mike Bywater
'88 80q (Lovin' every minute of it!)