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94 Corolla DX sold
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1,871 Posts
Discussion Starter · #1 ·
Seems lately there has been more talk on the topic of o2 sensors. I my self am due for a new o2 sensor at 173k miles. 94 DX CA emissions 1-wire.

There are two models(?) that I know of. 1 wire/2 wire(OE fit). Is that just the different standards emissions(CA, federal)?
 

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Sunny South Florida
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145 Posts
There are going to be many answers to your question. A NEW Sensor is surely going to respond to diagnostic needs better than a 173K one. Personally I prefer O.E. Might be a few more dollars however worth the mony for piece of mind!
 

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94 Corolla DX sold
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Discussion Starter · #5 ·
Of course I'm going Denso/OE. Why wouldn't I? lol

This was meant to be more of a discussion on o2 sensors and the differences for different emissions standards. And recommended brands/models(?). Not just for my instance of needing a bit of direction. I've seen quite a bit needing help in the last few days.

NTK sounds like it's worth looking into. Since we already recommend the NGK line of spark plugs for best performance(sounding like a commercial). I've never heard of NTK.
 

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1996 Corolla
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1996 1.6L 138Kmi 3-speed. Just had the original (i think) O2 replaced and now have noticeably improved idle. Overall response/feedback feels less jumpy, its a smoother drive. Waiting to see if oil consumption is reduced, but expecting next SMOG to show lowered emissions.

Still got that dang occasional ping/knock/predetonation
 

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Premium Member
1994 Corolla DX
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4,956 Posts
What about downstream O2 sensors? Do they make a difference in MPG?

Looks like mine would be a 2 wire for the downstream sensor.

Upstream Denso 2341053
Downstream Denso 2342051
Only function of downstream is to measure the efficiency of the catalytic converter so it can throw you a nice code if it's not working right.
 

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Sunny South Florida
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Only function of downstream is to measure the efficiency of the catalytic converter so it can throw you a nice code if it's not working right.
Not 100% true. The Primary concern is to measure Catalytic Efficency. It does have about a 5% portion of the driveability factor I have been told it is even worse on California Equipped Cars
 

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1994 Corolla DX
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Not 100% true. The Primary concern is to measure Catalytic Efficency. It does have about a 5% portion of the driveability factor I have been told it is even worse on California Equipped Cars
I believe that is true in "modern" cars. What I'm not sure about is whether the early OBD-II cars had this finesse built into their PCMs. I sort of doubt it?

Another factor to consider - that I don't know is true or not for this gen Corollas - is that a check engine code for downstream O2 sensor likely will throw the system out of closed loop. This will affect fuel economy.

So you're probably right that I'm not 100% correct in my statement. But I don't know how sophisticated the PCM is in using the downstream O2 sensor in these cars to control any portion of the fuel trim....
 

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1997 Corolla
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Notice any difference?

My preference is to try to make sure that everything else, like plugs, wires, cap & rotor are good, and that there are no exhaust leaks between the head and the O2, or any error codes in the computer, before putting a new O2 $en$or.

My understanding is that it's pretty easy to 'foul' an O2 sensor, if you're engine isn't running right for whatever reason.
 

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1994 Corolla DX
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Notice any difference?

My preference is to try to make sure that everything else, like plugs, wires, cap & rotor are good, and that there are no exhaust leaks between the head and the O2, or any error codes in the computer, before putting a new O2 $en$or.

My understanding is that it's pretty easy to 'foul' an O2 sensor, if you're engine isn't running right for whatever reason.
I agree with the approach you outlined. I had a tremendous improvement from replacing my O2 sensor, particularly at engine idle. But doing ignition maintenance and addressing any leaks first seem like a sound approach.
 

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Discussion Starter · #18 · (Edited)
Cap is on the list to be replaced but I don't think it's bad. Any I should look at for new cap? I've done the rotor(2500ish miles ago), wires and plugs a while back(20k ish). No exhaust leaks that I am aware of. Engine is in good health more or less as far as I can tell.

So far I'm not noticing a difference. But I do a lot of <5 mile trips. Majority is city. I'm averaging ~22-23mpg in city and ~26 freeway right now. I have a full tank now so it'll make it easier to notice an mpg increase or drop.
 
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