Re: O2 sensor cking

[PDQSHIP@aol.com]

In a message dated 96-04-20 22:48:09 EDT, you write:

>
>> As part of the 60k check it says to replace the o2 sensor.  Audi's price
>was 180
>
>Bosch designs the regular O2 sensors to last 60,000 miles.  They go 
>downhill very fast after that, although some last alot longer.  That is 
>the reason for the 60,000 mile recommendation.
>
>

An O2 sensor when bad will exibit some interesting behavior....  Basically,
O2 when the wear out will become "slow" to respond to the given O2 (or lack
thereof) in the exhaust...  This can actually be "seen" on the diag port for
the lambda freq valve...  A new O2 will (and here is a good use for your old
analog dwell meter) have a greater fluctuation for a given idle...  Say you
want a 42%DC at idle (thats 38 degrees on a 4cyl dwell)...  An old O2 will
fluctuate between 30 and 60 degrees, a new/er one will only show rock steady
or minor fluctuations say 35-45 degrees...  move off idle and the old one
will fly all over and is noticeably slower to react to any throttle
change....  A newer one is quicker and will tend to find lambda=1 pretty
quickly....  I did one on a 89 100 q just the other day, and the idle was so
bad the car stalled from the rich to lean fluctuation (90k on original)....
 A quick and dirty test is the loading of the engine with the ac on....  Most
bad O2 will make the car idle below the 950 stock idle and will stumble when
ac turned on....

Scott