o2 Sensor

[geo tracker 37145]

How do I check to see if my o2 is bad? My gas mileage is dropping and I know this is a symptom of a bad o2 sensor but I want to make sure this is the problem before I spend $75 (U.S) on a new o2.. Thanks,

[jtgh]

qod:
what is your gas mileage?
how many miles since a tune up.
what speeds are you driving. city , hiway or hiway& heavy traffic slow?
lots of idling.

this car is 25 city 29 max highway. (us gallons not imperial for you why North readers)

if it is a engine related issues, it can be:
ECT reading too low (temp full time)
engine not reaching normal temperature.
but it all depends on how far the MPG is off, just at tad or way off.

we get them here with 15mpg, that shows limphome mode is activated.
or FPReg stuck closed, or many things.

the chances of guessing are low.
but if you O2 is over 100k miles, then it can almost be assured the MPG will raise.
assuming the car ever enters closed loopl.

is the CEL lamp ON at keyon, not started and then does it go out after starting.

cheers.

[jtgh]

o2 on flee bay , bosch , chearer.

pn bosch.
testing-Oxygen sensor

15701 Federal only.
oem style with plug.

you need to id car, is it cal car or not, fed.
smog sticker under hood tells you this fact.
this is true for all pre 96 kicks and some after.
sticker req. by law in USA.
thanks for telling your location, it REally HELPS.

CHEERS.

[geo tracker 37145]

It has 140,000 miles but I don't know if it has ever been changed. I have recently put a new distr/rotor,plugs,reg service every 3,000 miles, oil,oil filter,air filter,and new computure about 2 years ago. I mostly drive on two lane country roads around 45-50 MPH with not much idling. It is curently getting around 21 MPG (mile per gallon) u.s In the summer it was getting 27-28 however it is winter here now. I never let it idle no more than just a min cause I no idling kills gas mileage.

[CodyJ]

Yeah you are right -- but in warmer weather.

In colder weather its best to let the engine get warm. When an engine is cold it consumes more fuel than when hot, so on hotter days you get the best MPG because the car spends less time trying to warm up by increasing fuel to do so. I doubt an O2 sensor would help if you were geting 27-28 during the good summer months.

[jtgh]

that is correct and a hundred other reasons too.
stiff fluids in axles and tranny.

slow traffic do to slippery roads.
but he need to state how bad it is , as that says what might be wrong.

best is to have a fast warm up o2 , as his has. if working.

also not idling car at first start in AM.
run for 45second then drive slowly until you see stat open (on gauge)
the move above 45mph , gives best mpg.
45 is sweet spot
and the added benefit is less engine wear .

they learned this in germany ,long ago, using a very accurate Nuclear testing method.
it was repeat here, and found to be true.
the wear is measured by detecting radio active wear dust in the oil.
fancy , huh? cant do this with micrometer. sorry. (unless you are rip van winkle) lol

that is why remote starters stink.

faster the warm up the faster the activation of closed loop.

i can tell you my 91 never give below 25mpg, ,even last month ,driving rt 80 miles to work on ice. so that is a low num.

did that tune up include quality wires?

on mine, both the iat and iac were both drifted low (cold, or higher resistance the spec)
i replaced both when i found that. EG 45f out side, it reported 25f or lower.
this makes all starts very rich.
The next thing is make sure engine reaches full 180+ deg f. and not low for some reason.
lift wheels , spin them , make sure not dragging.

no one has the Vulcan mind meld box (obd1 tech1 tool anyone it seems).
so all readings have to be done fred flntstone way, DVM meter.

are you sure you are not dragging feet?
and fred sometime forgets to raise feet on long down hills. hahahaha

it is a huge list.
Bad-GAS-Mileage-Poor-MPG

i agree ,it is cold winter driving, and one more thing.
IAT/ECT drift.
and or , O2 is old and slow ,as they all do about 80k on.

but gas is so cheap, like only about same as bottle water.
i think cheaper than ever (60 to present) adjusted for inflation.
but , you want to save carbon , that you get 10 points for...

the two thermo sensors are a snap to test
wait till cold morn. then pop off conn. (has locks dont force them) and put meter on
R x 20k range. and read it or auto range ohms.

and see this for data.
actual factory and real devices.
temp-sensors

same year too.

[jtgh]

best is drop on ice water,
should read 6000 ohms.
best test 1
2nd is boiling water.
and read. 200 ohms.
if close to this car will have intrinsic AFR mix accuracy, leaving only the o2 to do all the fine tuning.

cheers.