Sami951

It picks up air in your exhaust gases and tries to figure out your a/f ratio from that. All cat-equipped fuel injection engines pretty much need one to adjust fuel delivery on the go... without cats it's not that critical (I think I don't even have one in my car, but I haven't checked).

Danno

"what the hells an o2 sensor and whats its purpose?? "

Couple of links:

How Does The Oxygen Sensor In A Car Work?
About: Oxygen Sensors
http://www.kemparts.com/TechTalk/tt07.asp
http://www.scuderiaciriani.com/rx7/O2_sensor.html
http://www.volksparts.com/o2sensors.htm
http://autorepair.about.com/library/faqs/bl167b.htm

Related links:

How Car Computers Work
CD Player Converted to Nerve Gas Sensor

Bri Bro

Danno, got some broken links.

Modern O2 sensors do use the wire bundle to transfer O2 into the sensor. A long time ago, they put a small hole in the top of the sensor but it keep geting clogged with oil and dirt. So, some clever person said lets let the O2 pass throught the stranded wire. If you solder the wires, you stand a chance of blocking this path, but the o2 could still be transfered in the air gaps in the insulation, so it may still work because it takes only a small amount of O2 transfer to make the sensor work. Do you feel lucky?

Magown

I've soldered in at least 20 generic 02 sensors over the last few years. Not sure if they worked as good as when the car was new, but they all worked better then the 02 sensor I took out.


Fast951 John, are you recommending using something like a butt connector?

Danno

"Danno, got some broken links. "

Whoops sorry, just grabbed those off my bookmarks list without checking. Time for some housekeeping.

Yeah, it's not a conductivity issue with the solder, since a lead/tin solder will usually have 1/4th the resistivity of a stainless-steel wire. If getting air-flow down the wire is an issue, can we just poke some small holes in the heat-shrink tubing on the sensor side of the joint?

washington951

fast951 - just wanted to thank you for pursuing this thread. we may have different opinions, but its all about knowledge here. i really appreicate your postings - thanks!

fast951

Washington951, the pleasure is all mine. Debates are very productive, and when conducted in a friendly manner can be fun.

Peckster

I assume when Bosch says connection cable they mean wire? If so, there's air flowing between the tightly packed strands of wire underneath the insulation to the sensor itself? In that case I guess solder woud restrict the flow of air.

I guess you wouldn't want to completely cover the connection with heat shrink tubing, or the air would have no way to get in, right?

One other question, with pressure in the exhaust system, how would air get drawn in?

Bri Bro

The tip that is exposed to exhaust gas has a porous ceramic coating (Nernst cell) that conduct O2 ions when heated above 350 C. THe other side of the that is expose to outside air is open. Since the cell is conducting ions of oxygen, even the small gaps between the stranded wires is more then enough.

http://www.sts.sae.org/membersonly/t...xygen13-17.pdf

evil 944t

Anybody ever use a 4 wire? What wires go where?

Danno

The only extra wire in the 4-wire sensor is the ground for the signal. You'll have to run your own ground wire and use the grounds for the other sensors on the DME #5/26/27.

DangerIsland

Danno, and everyone...

Is there really no reason to run an O2 sensor if you don't have a cat? As I'm rebuilding my 951, I'm thinking about parts I need, and the O2 sensor was one of them, if I'm going to be running an open exhaust, is there no need for one (this will be a street car, k27/6, guru chips.)

fast951

You should run O2 sensor. The DME runs in closed loop and uses the O2 sensor's signal to make adjustments.

rhesus

Sorry to be slightly OT, but I'm going to be adding an A/F gauge in my car fairly soon, using the stock o2 sensor. I know it's not the greatest but it's better than nothing. Anyways, where do you guys tap into for the gauge? I know boost usually goes to the KLR, and I'm wondering if there's something closer than the o2 sensor itself... TIA!

Jake951

You can tap into the O2 sensor signal at the DME. I believe it's pin #24 on the DME, but I'll have to check the DME schematic to be sure.