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Should I replace my O2 sensor?; Just got a new to me 1994 Metro with 170k running
Topic Started: Aug 11 2012, 09:34 AM (1,305 Views)
cwatkin


I just got my 1994 metro engine swap completed and have the car on the road. The bad engine had 154k miles on it while the good one has 170k miles. I have no idea if the O2 sensor was ever changed on either engine but would expect maybe not. My only check engine light was in no way related to this so it isn't terrible.

I haven't owned an OBD1 car before so I was wondering how much input the O2 sensor has to influencing proper running and efficient operation on a Geo Metro. I did get this for the mileage after all and want the best mileage possible. Plus, the engine will burn cleaner with less change of fouling things if I understand correctly.

My last experience with O2 sensors was on an OBD2 vehicle. The truck was running really rough and getting terrible gas mileage. I gave it a basic tune-up which it needed and things improved very slightly but not much. The truck came back to life and ran like new and got much higher MPG after I replaced the O2 sensors. This went on for a couple months while I tried to figure out what was wrong and never saw a check engine light. I guess the readings from an O2 sensor need to be really off to throw a code.

Is this something you should replace for good measure or not worry about? Although this engine has 170k, it is in good shape and obviously had reasonable maintenance done on it. The oil had been changed enough that it doesn't smoke and still has lots of power... at least as much as you could expect from a Metro which is more than I expected.

Thanks,

Conor
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crankcase


Congratulation on a sucessful swap. How is it running?

If it were me, I would not worry about it unless there were evidence it needed it. Check engine light code 13 is for oxygen sensor, and you can do voltage checks on the sensor line as well to check things.
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cwatkin


Thanks. The engine seems to be running great and better than I expected. It is a tight engine with plenty of power and doesn't seem to smoke/use oil. I added some MMO and noticed the level dropping which I guess is normal as it gets heated up and vaporizes through the PCV. I am adding only oil now and will see if the level continues to drop which I suspect it won't much. Besides this, the engine is definitely a good runner. Seeing the car it came from would not make one want the engine from it but I think this was a good one! I also did the cap/rotor as well as plugs and wires.

The reason I ask about the O2 is that I understand these often don't last more than 80-100k before degrading. I didn't get any codes on my truck but things changed for the better when I changed them. What are the signs besides a code 13?

Thanks,

Conor
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Norby
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I wouldn't touch the O2 unless needed. If it's running great and your mileage is satisfactory then it's fine.
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mwebb
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FOG

if you do not have a scope
you can not test your 02 sensor

engines that burn oil kill 02 sensors very quickly by coating the thimbles with oil deposits.

if you have a scope the 02 sensor waveform at cruise should look like this
Posted Image
the upper dark trace is the 02 sensor at about 45mph at cruise
the 02 sensor waveform is showing slight misfire

but shows good amplitude and good rate of change , good but not great... the injection system on this car can not respond rapidly

if your 02 sensor has low amplitude or can not change state in 100ms or less at 2k rpm hot
your cat converter's life will be shortened and depending on the failure your 02 sensor has
your fuel economy may be degraded

Posted Image
this 02 sensor (red trace) would look "good" to a DVOM
but it is very bad
it can not change from rich to lean in 100ms or even 300ms

so yes
change your 02 sensor
but do not bother if you are going to use a low quality white box chinese part they are all bad ,
over half of the white box chinese 02 sensors test bad right out of the box
none of the survivors last very long
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cwatkin


I think I have a buddy with a scope I could borrow to give this a look. I would get a Bosch, AC Delco, or whatever, not the Chinese crap, when I decide to replace the O2 sensor. I don't think the car is burning any oil. I have driven it 100 miles since I checked the oil last and can't see any drop in the level. I was asking a mechanic about why you don't see near as many super polluting cars as you did 10 years ago today and he indicated that the newer cars simply have too many sensors that cannot take the contamination from oil burning. You either have to fix it or junk it. Simply adding oil doesn't do it anymore with modern vehicles.

Conor
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