O2 Sensor.. Alert ! ..and new info

[dfink]

God I hate to even bring this up again. After reading the thread and thinking about it a bit I got to wondering why there is such an elaborate connector for the O2 sensor. If it only needs an electrical connection why not just put a regular connector on it. Now I don't buy the idea that it goes all the way back to the DME unit but perhaps that connector has some function such as air source to the main wire or perhaps it has some sort of RF shield for signal. Perhaps there is more to be looked at.
I will now hang my head and wait for the ridicule.
Why do I do these things.

[Wil Ferch]

I've pretty much convinced myself that the Bosch rep was either ill-informed or just plain wrong in his own thinking.

There seems to be enough empirical data that properly spliced connections will work.

I'm kinda ashamed to have given this argument credence in the first place...but holy cow...he IS a rep of the OEM supplier...who was I to say he's wrong !!

- Wil

[Zeke]

Well, you did put forth the idea that the Ford sensor is a viable subtitute as part of your oiginal thesis. For this, I offer my thanks because I have one in my car now. I'll go check and see how good a job I did on the coneections, though. I didn't do marine connectors or tin the wires, that I can tell you. I'll start doing this.

[dfink]

Originally posted by Wil Ferch

There seems to be enough empirical data that properly spliced connections will work.
- Wil

I am not doubting that a spliced connection would work. It would let tiny amounts of air in even if the air went in around the spice. Common sense must be employed. There is no way it is pulling a vacuum all the way to the DME and is probably not a vacuum as we traditionally thing anyway more of a path. It may be sealed as OEM to the first connector but may not matter unless you are an engineer. Point to ponder why this may be true.

Why is there that fancy connector instead of just a regular spade type. However connector type might not mean anything. The temp and pressure senders use a totally different connector so maybe that is just what Bosch decided to use.

I would however have liked to see the machine that pressure tested the wires. I will now let this die as I should have never resurrected it anyhow. Maybe that connector has a hidden piezo electric micro pump.

[Wil Ferch]

O2 sensors need a reference source of air and some are designed with purposeful openings somewhere on the sensor body... to the atmosphere. It's usually this type of design that gets mucked up in 911 service, with wheel-spray and such.

The "Stock" design somehow gets air via other means, as the sensor is a "closed" design...the Bosch rep says microscopically pulling air from under the wire insulation. Dunno. Maybe if it actually works this way it's OK to pull at the first point of connection..like in the engine compartment plug.

Either way..it's confusing....and the connector used may be answered as simply as you state.. perhaps for no real reason at all, or maybe it tolerates local engine environment well....as the connection can conceivably be made inside the engine bay ( more ideal) or closer to the cat ( less ideal).

????

- Wil

[ischmitz]

I think it is time to talk to these guys....

[Bill in OKC]

I have done a lot of internet sleuthing on o2 sensors because my Ducati runs like crap with the o2 sensor plugged in - and not too bad with it disconnected... anyhow I have read in several places that the reference atmospheric oxygen is in many cases routed through the wire insulation. It supposedly only takes microscopic amounts of atmosphere for the thing to compare to the exhaust gasses and work properly. I don't think it needs to necessarily go all the way back to the computer - just a port somewhere away from the road muck.

[Mysterytrain]

Found this on 'the google' ..ck out the last sentence:

"The probe tip, which is shaped like a small rocket nose cone, is made of high-temperature ceramic that is coated with a very thin layer of platinum that forms an electrode. The tip is protected by a slotted metal tube that allows exhaust gas to flow across the outside surface of the probe. Provision in the sensor body or wiring assures that the ambient air fills the inside of the probe tip.

[dlagerstrom]

I make wire and connectors for a living.

I know for a fact that 'air' will travel in an insulated STRANDED wire. Water will as well, over time. Once you solder the wire strands, the path for air is fairly blocked as the air travels between the strands. I believe it is plausible that the air enters the system at the first cut in the insulation (the connector) and does not count on travel all the way back to the computer.

There is no way an irradiated PVC insulation (as supposed in an earlier post) will last for 20 years next to an exhaust system under a car without potential leaks. If the sensor is only good until the insulation fails it would be a pretty poor design. Irradiating is a method of cross-linking the PVC molecules to provide a wider temp range for the plastic.

[Mysterytrain]

Ok, I also found a couple of pictures that might explain the 'air thru the wire'




The second picture is from Pelican



You can see the rubber strain relief on the sensor followed by the shrink tubing. I'm wondering if the Bosch guy was refering to this?

[Bill in OKC]

Here is another description:

http://www.aa1car.com/library/o2sensor.htm

"The outside of the bulb is exposed to the hot gases in the exhaust while the inside of the bulb is vented internally through the sensor body to the outside atmosphere. Older style oxygen sensors actually have a small hole in the body shell so air can enter the sensor, but newer style O2 sensors "breathe" through their wire connectors and have no vent hole. It is hard to believe, but the tiny amount of space between the insulation and wire provides enough room for air to seep into the sensor (for this reason, grease should never be used on O2 sensor connectors because it can block the flow of air). Venting the sensor through the wires rather than with a hole in the body reduces the risk of dirt or water contamination that could foul the sensor from the inside and cause it to fail."

[livi]

What a relief I have a ROW model without that tricky little sensor! I am such a tech ignorant - havn´t the foggiest what you are talking about.

[ischmitz]

Bosch and others offers generic sensors with crimp-connections. They would not do that if they insulation was required to be intact all the way to the DME to guide air.

The Nernst cell in a narrow-band O2 sensor requires a path to the ambient atmosphere to work and the amounts of air required are tiny. But you don't require the air to travel along the insulation all the way to the DME. It can diffuse into the ceramic opening at the wire end of the sensor.

[Mysterytrain]

Hmmm looks like Wayne is down a hundred bucks and radcon a cool 'G'

[glenncof]

Bosche 15735 universal is what I used on a '85 911.

I did a lot of study since I had three vehicles needed sensors.

I'm a electrical engineer so my first thought was soldering. I read about two issues; solder resin clogging wires and the wires themselves being very hard to solder due to the material. (I don't know if this applies to 911 app or not.)

I ended up using crimp on clips. Initially tried to install on the 911 with Bosche Universal connection block but it would not fit through fendor hole.

[Chuck Moreland]

Sounds like a reference sample of air is required. If the wire is spliced, that sample comes from the spliced area adjacent to the sensor - and that works just fine provided the opening remains clear.

But by design the sample comes through the sheath. The vent is then moved back to the first opening in the sheath, strictly for the purpose of moving the vent to a cleaner, dryer location.

Seems reasonable to me.

[dfink]

What is the interest compounded on a five year old thread.

[911 tweaks]

great info here guys. For the O2 sensor challenged, ;-) :
1. would someone please summarize what if any universal sensors can be used? How many wires? Mfgr & P/N
2. how should they be terminated to a Porsche? connector?
3. Is there an insulator/shrink tubing needed for the wire(s)?
**Please answer for SC's and Carrera's**
Thanks, Bob

[glenncof]

www.boschautoparts.com/NR/rdonlyres/D90D5AD3-7E41-439E-B271-20A76139E0F7/0/OxygenSensorInstall.pdf

See above for universal replacement. I used crimped connections to fit thru fendor.

Bosch USA site.
www.boschautoparts.com/

[SCWDP911]

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