[mwebb]

these areas as identified in this dated EPA link
are where the greatest / worst tampering with the fuel are

Where You Live | Reformulated Gas | US EPA

i happen to live inside of an "Opt In" RFG NON Attainment area ....
my fuel economy is 20% off from others with similar cars in other areas
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for those that have an interest
to test your 02 sensor s

you will need a scope ,
the 02 sensor must switch from 150mv to 850mv and from 850mv to 150mv in 100ms or less at 2k rpm hot .

if it does , it is "good"
assuming the 02 sensor heater is also functioning as designed

on OBD2 systems -
those of you who have the ability to view
Mode 5 or Mode 6 can look up the TID for the CID for the 02 sensor in question .... however those test results may pass an 02 sensor that would FAIL the above test .
when in doubt
the test above supersedes all other tests

the 02 sensor below passes the Mode 5 test
but
fails - this Bosch 02 sensor is brand new and DEFECTIVE
(new really means Never Ever Worked)
it does switch from 150 to 850mv in less than 100ms
but from 850 mv to 150mv takes much longer .....
KAKA - you can not see this without a scope


scan data showing 2 front 02 sensors , one is bad the one that takes too long to change state
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AS you can see -
an emissions test pass or fail is not a good way to identify a bad or failing 02 sensor
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on a speed density system
with a MAP sensor as primary load sensor
a vacuum leak will result in rich condition with retarded ignition timing

NOT lean condition with advanced ignition timing

because
MAP = Baro - Intake manifold vacuum

so when intake manifold vacuum is reduced due to vacuum leak
MAP is increased so Load is increased
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sometimes
this site is like watching children bickering - many of you know a great deal and many of you know just enough to get in trouble ....
remember why we are all here
to improve our fuel economy
try and work together to exploit each others strengths ... and overlook the minor errors and weaknesses

we are all on the same side