My 1995 850NA is mostly short trips stuff around town.
When It gets on the highway and has high rpm to get up to speed then I start
getting OBD codes: A2/ 443 435
I started looking around for O2 sensors and the prices are all over the place.
has anyone done business with:

http://www.discounto2sensor.com/store/?N=0&Nr=AND%28category%3AExhaust%2Cuniversal%3A0%29&PN=2219&VN=4294967170+4294958614+4294963913+4294958609+4294958787&Nr=AND%28category:Exhaust,universal:0%29

They have a wide assortment of O2 sensors.

FCP offers Walker and Bosch way less than Tasca for Volvo OEM

Should I be thinking about changing out the front sensor
I get about 17MPG around town and 26MPG on the highway dragging a couple of bikes.

I don't want to spring for an O2 sensor just because the computer gets surprised that the RPMs go high.

Would a new sensor or sensors improve the around town mileage?

Bill

I'd just grab a couple from the junkyard at $10/ea, that way you have redundancy. I'd grab rear sensors as they tend to be much better treated (and not taken as often). They're the same sensor with a longer cord, just make sure to secure the extra cable to something, you don't want it dragging under the car!
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If you're not driving it "like its stolen," are you really driving?

I haven't found out where the 850 O2 sensors are, can you get em from the top?

My last experience with an o2 sensor was in a 740 (B230F) and it was welded in and
needed to go on a lift and get blasted with OxyAcetylene, and finally came free
with lots of gusto using a large pipe wrench. UGH! Might have been easier to
blow it off with gelignite?!@ (Maybe the previous owner used epoxy or Loktite instead
of Neverseez)

Apparently 850 O2 sensors are really a different and more cooperative critters?

Maybe I'm wrong but, why do I think boneyard O2 sensors will be a bad idea?

Bill

They're quite easy to change out, should take less time than an oil change if you've got the tools/location down. First unplug them (pull up on the clip then pull out on the plug) then pull out the cord from the underside. All that's left is unscrewing the plug from the pipe. If you've got the plug off you can use a closed wrench (feed it up the cord), otherwise an open wrench or an O2 socket.

I've put about 25k on my front one from a junkyard, so far so good..
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If you're not driving it "like its stolen," are you really driving?

The 'front' O2 sensor is on the down pipe, the 'rear' is after the CAT.

Both electrical connectors are together, you can see the boxes looking down between the air box and block, close to the firewall. They sit on the tranny.

To disconnect the electrical connection at the coupling, use a small screwdriver and pry the top of the box up. They are stubborn because of grit and dirt, but they will come up about 1/2 inch. At that point, the plug can be pulled out from the bottom of the box.

The O2 sensor can be hard to get out, a 17mm I believe. Best to reach up from underneath.

Klaus
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Did you do your Random Act of Kindness today?

Cleaning could be efficient for old not heated sensors where soot was coating platinum catalyst. New heated sensors they are heating ceramic sensing element above 300 o C and soot should be burnt totally. Gas contains always certain amount of mineral matter which is producing ash when burned. The main component of ash is silica which is coating the platinum element of sensor decreasing its efficiency. There is rather no way to clean this ash without damaging the sensor. I would replace each sensors after 100,000 -120,00 miles. I did experiment and found that sensor after 110,000 was responding much slower to change of the amount of oxygen than new one. The OBDII system did not complain but definitely the sensor was not performing as new one.

My sensors are likely original with about 200K miles on them.

What happens to the engine when the O2 sensors degrade?

Will replacing the front sensor improve mileage and/or engine performance?

Is there much difference in the performance and reliability/longevity of the
various O2 sensors?

The rear sensor is after the CAT which 'cleans' the exhaust. Unless the CAT goes bad, the rear sensor usually survives quite well.

Klaus
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Did you do your Random Act of Kindness today?

Hi, having had 2x850-94 n/a for both the o2 has been cleaned once at around 250kkm.
the other was responding slowly in inspection, hardly reaching acceptable results.
after cleaning no problems this kind.the other I cleaned last summer just for better mpg.
I used carbon leaner liquid and garden grill to burn the sensor clean and dry a one hour job all together.
br tapsa

The $105 version looks pretty good. I would avoid splicing wires. Just replace the front sensor, the rear has no errors yet.

Yes, you should be getting 20+ around town. But do not use regular gasoline! It tends to burn too hot and foul the sensors.

Klaus
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Did you do your Random Act of Kindness today?

Has anyone tried to clean O2 sensors before resorting to replacement?
what is it that fails or degrades with O2 sensors?

BB

You must not rub them with anything. Yes, they can be cleaned.

http://www.volvo-forums.com/t19099-is-it-possible-to-clean-the-oxygen-sensor.htm

Klaus
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Did you do your Random Act of Kindness today?