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Bad o2 sensor 27 mpg on a 3 cyl 5 speed?; is this possible ?
Topic Started: Apr 25 2011, 10:23 PM (3,012 Views)
ogoz23
Elite Member
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Hi I have a 2000 geo metro 3 cyl 5 speed i drive very conservative and I'm getting 27 mpg I have the check engine light and it shows a code for the upper o2 sensor can this be the cause of a bad o2 sensor??? It seems pretty extreme specially sinse I hear this cars get 45 mpg a 40% drop on mpg seems pretty extreme :stoner
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GeoRating
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Wow. That is extreme! The upstream O2 sensor tells the car when to burn less/more fuel and most likely is causing the car to burn rich. I'm not sure if it can be to that extreme, but if the O2 sensor is telling the car it has to put more gas in continuously it could be running at its max all the time... Like when my downstream O2 sensor was bad, it was constantly reporting one solid high number.
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dayle1960
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Fastest Hampster EVER

Are you throwing a cel code?
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ogoz23
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yea the code was for the upstream o2 sensor i changed it today i also did a compresition test on all 3 cylinders and they all where 150-153
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GeoRating
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Compression is running around the bare minimum, same as my metro. It most likely needs a rebuild soon enough. Has it been getting low MPGs since you got it, or is this a new development?
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JohnDN


Hmm...I'm only familiar with OBDI Metros, but the only way any of my metros got into the 20's MPGs was when the MAP sensor either went bad or the vacuum hose or electrical connector became disconnected from it.
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ogoz23
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I just bought the metro a week ago, I'm going to check the map sensor and just replace all the vacuum hoses just in case
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Bad Bent
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Facetious Educated Donkey

The other item to check will be the coolant hoses on the TB on the passenger side. Both should be as warm as radiator hoses get. They feed coolant to the Coolant Temperature Sensor on the TB.

Posted Image

But yes, a new O2 sensor is a good idea if the ECM says so. :-/
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mwebb
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FOG

..."But yes, a new O2 sensor is a good idea if the ECM says so. :-/"....

no it is not
the ECM is stupid , it only knows scenarios the engineers told it to know , if the 02 sensor heater circuit has a problem , the ECM will code for the 02 sensor
but
the 02 sensor will not be " bad "
so

you need to
TEST , do not GUESS .

the two white wires at the 02 sensor must have 12 volts between them
the grey wire is ground , within 50mv of battery negative
and the black signal wire , must cycle from 150 to 850mv in 100ms or .1 second and back from 850 to 150mv in 100ms or .1 second at 2k rpm hot

IF the 02 sensor is bad
the signal , Black wire, values will not be as above , and if the heater is not powered up then the signal , Black wire will not be as above and
if the ground is bad the Black , signal will not be as above .

all the ECM can see is that the Black signal is not as above - the ECM can not reason why , the ECM can be
WRONG .

get out your DVOM of DSO
what ? don't have one ? buy one ! yesterday

anyone who has a mind to can search this forum - type in oxygen sensor or 02 sensor or O2 sensor and
read
study
learn

TEST - Do NOT Guess.

or be a dork , just buy parts and throw them at the car , it is good for the economy .
after you pee away your money and become frustrated
bring the car to me or someone like me . and i will Test it , locate the real problem , and fix it .

thank me very much
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ogoz23
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OK well I'm a little late I bought the new o2 sensor and the code when away does this mean that was my problem or I still have to test ?
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Bigr2009
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I like ur style mwebb!!!!! But I work at a parts store and I dot ask ? I just sell parts. If u want em u got em. Lol. Like the guy that wanted spark plugs when he sprayed starter fluid in the tb. But yes testing helps. If u don't kno how, ask parts are salty!! (too much)
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mcmancuso
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You could still have a vacuum or coolant problem, check these things as well. They can all cause a rich condition.
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ogoz23
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how do i check if i have a coolant problem? the car doesnt over heat any other way i can check?
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mwebb
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FOG

ogoz23
Apr 27 2011, 10:09 PM
OK well I'm a little late I bought the new o2 sensor and the code when away does this mean that was my problem or I still have to test ?
are you still getting 27 miles to the gallon ?
if yes
you need to test ,
if no
you need to test ,
so that you know what "good" should look like .

and
some DTCs are two trip DTCs , they will not set until testing conditions / parameters are met for two drive cycles
and
some tests were disabled by the 02 sensor DTC , now
those tests will run as the testing has been enabled by the clearing of the DTC, do not be too surprised to find a completely new DTC or DTCs
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ogoz23
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im sorry i know i sound stupid but how do i test it you mean test the mpg? and what does DTC stand for , again i know its a stupid question
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