O2 sensors (4)

Anyone have a good knowledge of how the O2 sensors function on engines with 4 sensors? The manual I have doesn't go into any detail. I'm seeing error codes 171 & 172 which is sensor reporting lean condition on left and
right side. I would like to fix but not wanting to replace all 4 sensors if possible (car is going to be sold in not to distant future).
Mickey
96 CV 4.6L
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On Fri, 17 Oct 2003 10:25:56 -0700, Mickey

My explanation here is admittedly simplistic, but, your codes are related to signals from the O2 sensors at the engine. The other two are pretty much used to measure the performance and efficiency of the converters. With a lean code on both banks, you have an overall lean condition which would suggest a problem with either a vacuum leak or, a fuel delivery problem. You need someone who has a scanner that can provide realtime outputs to analyze the situation causing the lean condition. With the same fault from two sources, it is not likely that the sensors themselves are at fault or erroneous.
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Try cleaning the Mass Air Flow sensor.
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Neil Nelson wrote:

Why would problems with the MAF sensor result in error code for O2 sensor yet not be reported with a error itself??
Mickey
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On Sun, 19 Oct 2003 11:06:10 -0700, Mickey

The error codes are produced by the O2 sensors telling you that something else in the system is causing a lean condition. As Neil indicated, the MAF can and is known to cause this on occasion and, can many times be corrected by simply cleaning. There are instructions with pictures for doing that on the net. If you choose to do this, you must be extremely careful not to damage the small hair-sized wires in it. Now, forget the O2 sensor and pay attention to what they are telling you - they are only the messengers.
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The mass airflow sensor measures intake air mass by a heated wire which is monitored for amperage, as more air flows into the engine, the heated wire cools off, the cooler wire carries more amperage. If (when) dirt collects on the heated wire, it becomes thermally insulated -by- the dirt itself, this un-intended insulating effect manifests itself as air entering the engine than what is actually reported to the PCM by the mass airflow sensor. The classic definition of lean (the codes you have stored in memory) is too much air. Additional logic; you have a lean condition effecting -both- banks of the engine. What component can effect fuel mixture to -both- banks of the engine. The Mass Airflow Sensor!
Why no MAF sensor code? Simple, the MAF hasn't failed completely and yet it has no way to determine exactly how much air -is- flowing past it. Coolant sensors act the same way when they (or the circuit) slides out of calibration.
This is precisely why doing driveability repair work is much, much more than reading a trouble code and shot-gunning a part in the direction of the code! You -have- to know and understand the whole system, what effects what and why.
Now, you can squander $400-$500 on nice shiney brand new O2 sensors, or you can go to Radio Shack and buy a $2 can of tuner cleaner, give the MAF element a squirt, but if I've seen this problem once, I've seen it a hundred times...
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I have had problems WITH o2 sensors.... Cheapest test is to take o2 sensor out and torch it
take a blow torch and get the tip that goes in the exaust like pretty hot.. just not melting.. just before white hot.
Let it cool and try it. I got lucky you may too
Ken
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Neil Nelson wrote:

Neil, thanks for the explanation this was what I was asking for. If you read my other post (different subject line) you would see I am looking/including things that are in common for both banks. This is the first car I've worked on with a MAF sensor so lack of knowledge of this component is present. Typ manuals don't go into very much detail.
On the other hand, I've read in several locations O2 sensors are good for about 60k miles and this car has just turned 70k. If true they could be the actual problem but before throwing $$$ at it they will be tested for voltage output.
I don't swap parts until I stumble across the cause. As I said before I'm just trying to gain some knowledge on this system.
As another poster, lugnut, suggested several times, checking vac and fuel (common/shared components) was done before even posting the first time.
Again, thanks for the comments.
Mickey
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Glad to be of assistance.
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