93 240 nonTurbo, non-California

I replaced the O2 sensor 10 months ago with a Walker 3 wire universal. I soldered the wires vice using the crimp connectors they supplied. No issues until last week. 2-1-2 code. Good voltage readings from the sensor wire, about .57 volts and appropriate fluctuations when I created vacuum leaks or made throttle adjustments. Wire to the ECU has good continuity. Good +12V to the heating element. After idling for 10 minutes, the resistance reading in the heating element didn't change, always about 7 ohms. Not the 13 ohms hot or 3 ohms cold. So I think I've got a bad heating function in the sensor. Cleared the code. Drove it for about 4 days. Yesterday after a 2-3 minute trip. Turned the car off, returned in about 10 minutes, started the car as normal and there that check engine light is again... 2-1-2.

So, here are my choices, and I'm open to other ideas. It is still under warranty:

1. Replace it with another Walker 3 wire universal and solder it again. Warranty replacement.
2. Buy the direct fit plugin by Walker. $105 less $50 warranty credit
3. Buy the direct fit plugin by Bosch. $119 less $50 warranty credit

The motor is in great condition. I'm leaning towards buying the direct plug in because I don't want to jack around with the soldering again. I'm also leaning towards the Bosch because the one in there now is the Walker universal.

Thanks for listening/reading!

The instructions do say to crimp rather than solder, but that has never quite made sense to me. I have always bought OEM so I never had to face that decision.

I have never bought at Walker. I used to use Bosch, but have switched to Denso for my most recent replacements. Actually, the box does not say Denso. It is a subsidiary of Denso.

My 91 drove me nuts a year or so ago with an intermittant power feed to the oxygen sensor heater. Always worked when I checked it. Took forever to find the problem. I ended up running a new wire from the fuse box to the sensor plug. No more problems.

Walker was the last one I had in there. I should receive the Bosch one today with the entire cable. I like saving a few dollars, but sometimes I throw in the towel and not take the "cheap" route twice. Although I did learn about the possibility of buying the Mustang version with this thread.

All I have is 1 data point with my Walker Universal heating element failing at 8 months. Not sure if that is a design or manufacturing flaw. Glad there is an aftermarket out there to keep pricing competitive.

First of all the reason you don't have accurate O2 readings is because you soldered the connections instead of crimping them. When you solder the connections it doesn't allow the wire to breathe. This is very important.
Your ecu is probably compenstating for the erroneous readings from the O2 sensor. The O2 sensor isn't in the "loop" for the first couple of minutes until it heats up. That's why there are 3 wires going to it. One for the actual sensor and two for the heater.

Second I have read from other Bricksters that the Walkers are junk.
Mcduck suggestion is the favorite among the people on this board. It's the cheapest solution with the longest lasting results.

I appreciate the comments on the Walker O2 sensor. I'm going with the Bosch.

However, I have to take issue with the comment on the "wire to breath" for the sake of all who read these posts. You comment has no basis in fact or current knowledge. Soldering is a proven technique to reduce the potential for increased resistance caused by crimp style connectors and the associated issues of corrosion, etc. With such low voltages, it is important to manage resistance. I am not an electrical engineer by trade, but I've spent the better part of 30 years working with some of the finest in the civil and military sectors. I have never heard them say "wire to breath".

This forum is a great resource and what can make it better is to correct misconceptions quickly and politely.

Cheers!

I make stuff for NASA: Soldering of wire connections is discouraged, for a number of reasons.
1) you don't know how to do it.
2) it makes the wires brittle.
3) crimping is MUCH more consistent.

I've replaced ~5-6 O2 sensors with cheap 3-wire Bosch.
Never a problem.

Crimp FTW!

"However, I have to take issue with the comment on the "wire to breath" for the sake of all who read these posts. You comment has no basis in fact or current knowledge. Soldering is a proven technique to reduce the potential for increased resistance caused by crimp style connectors and the associated issues of corrosion, etc."

I'm compelled to take issue with that comment (for all who read these posts) to show that there is actually a lot of current knowledge about how the O2 sensor gets its "reference air" and how to splice sensor wires.

Because the Oxygen sensor is constantly comparing the Oxygen in the exhaust stream with air outside the engine, a source of outside air is essential. Soldering the stainless steel wires is generally not advised, when the question is raised. I believe that's why "Universal" O2 sensors come supplied with crimp connectors for splicing.

Google searching turns up many sources to back this up.
Here are a few...

===============================
[choose 411]
STEP 4:
A) On universal sensors where heat-shrink tube(s) are already installed: insert just striped portion of wire(s) into crimp terminals of new sensor and crimp the terminals
B) On universal sensors where heat-shrink tube(s) are not installed: insert just striped portion of wire(s) into crimp type "butt" connectors (approx. 1/4") and crimp.
===============================================
CLICK
You should never solder a O2 sensor wire because the sensor "will breathe" through the cable. The acceptable method of splicing or repairing O2 wiring is with crimp connectors. This information was from Bosch Technical Staff in Europe.
=====================
CLICK
Oxygen sensors compare the oxygen content in the outside air to the oxygen content in the exhaust. The outside air is brought into the sensor either through a vent in the sensor housing or through the wiring connector itself.
===========================
CLICK
If you are replacing the O2 Sensor with a universal replacement sensor, you'll have to splice the factory connector plug onto the new sensor. ... DO NOT solder the connectors onto the wires. They must be crimped on for the O2 sensor to work correctly. For the sensor to work correctly, it must draw clean air down to the sensor through the air gaps in the stranded wire. If you solder the wires, the solder will fill the air gaps in the wire and the sensor will not work correctly.
=====================
CLICK
Many older sensors have a vent hole in the side of the sensor for reference air. These could easily become plugged with mud or splattered squirrel parts. For this reason, newer sensors "breathe" through their wire connectors, allowing air to travel between the wire and insulation. Grease in these sensor connectors can cause the reference oxygen to be lost.

--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

These threads are kind of odd. Everyone keeps saying they have soldered them but solder will not stick to the wires on my O2 sensor. It may be stainless wire? I've tried a few different kinds of solder even Silver solder and nothing will stick. Are all these people claiming to have soldered there's just keyboard warriors spouting about something they have not done? I was a repair tech at Telcom for a year and have wired hundreds of motorcycles and cars from scratch, I don't use those cheesy kits and duplicate the original harness usually.I have several types and thickness of solder for different applications. Does anyone know of a type of solder that will work?

I agree with you based on my experience. I've never tried to solder those wires because I can feel the hardness of them to know they aren't copper and by feel, must be stainless steel. But my experience isn't everyone's and perhaps it is possible there are oxygen sensor cables out there that aren't like mine.

But I'm not sure I agree with your "cheesy" characterization of the universal splice kits. Well maybe cheesy. I've used them twice in years past (not on Volvo) and was impressed by the physical security and ability to exclude the elements, or at least that's the impression that got left in my memory. But of course, having the original harness length and connectors does a better job if affordable. No one wants electrical connections (splices) exposed to the road under the car regardless of how well encapsulated they appear to be.
--
Art Benstein near Baltimore

Pilfered from Eric:

The Parts Man Prayer

I work behind the counter
In an auto parts store
Sometimes I'm called a genius
Sometimes I'm called much more.

I say I'm no mechanic
But when their job goes sick
Everyone comes in and asks me
What makes the damn thing tick.

I'm supposed to know the number
Of nuts and bolts and gears
For every machine ever made
For more than a hundred years.

I'm supposed to have the answer
For everything unknown
To every Tom, Dick, and Harry
For all their questions thrown.

My life would be a pleasure
And I'd grin from ear to ear
If only they would tell me
Their Model, Make, Year

TOkay, you guessed correctly, I had to reply. :-)

What we are talking about here is soldering or crimping connections about 18" from the sensor. Presuming the Walker Universal is the "breathing" type soldering that far up stream would be inconsequential. Further more, Walker, and others, supply heat shrink tubing to go over the crimps. So given a proper and tight crimp and then covered in heat shrink could defeat/restrict the "breathing". I am suspicious of claims of insulated wire's ability to breath the +60" of a Volvo's factory harness, no crimps. Look at the end of the O2 wire at the connector in the engine bay. I don't see any "air passages" and I do see a weather tight seal. So what is one to do?

I like to work from facts and data, and I like to tap the knowledge of experts. My question today to Engineering at Walker Products regarding their Walker Universal 250-23000: "My preference is to solder the connections and enclose the connection with heat shrink. The instructions in hand only speak to the crimp style connection. Any issues or concerns with how I want to do this?"

Walker Products Engineering response: "Soldering connections is acceptable. Make sure there are no sharp points of solder or wire that might pierce the heat shrink tubing. When installing the sensor, make sure the solder joint is under minimal stress, so that it is not stretched or vibrated during driving."

That's good enough for me.

Soldering may be "acceptable", but to me the manufacturer-supplied crimps are "approved". I don't want to drag this on but would like to make 3 points, which I'll expand on as briefly as I can...

1. The O2 sensor absolutely requires a (minute) supply of reference air to generate it's signal voltage.

2. The inherent difficulty of soldering stainless steel (fluxes, heat etc.) potentially risks the sensor's access to reference air via the signal wire.

3. The possibly superior conductivity of a soldered sensor signal wire splice is not needed.

(1) Early sensors got reference air from a hole in the sensor capsule, but not any more. Most sources say the air now comes in via the wire. I accept that because there seems to be no alternative.

(2) Assuming that the air access is through the wire, soldering those stainless steel strands could introduce flux run-off or, in the case of silver soldering, the need for possibly corrosive fluxes and high temperatures.

(3) A simple on-the-car exercise will show that the ECU does not need the potential super conductivity of a soldered splice...

With engine running at a warm idle, disconnect the sensor from the ECU (idle speed may change a little). Hold the ECU terminal with one hand and touch the Battery + terminal with a finger of the other hand.

Your body will carry a weak positive potential from the battery, that ECU "sees" as a very rich signal from the O2 sensor. In response, the ECU will drastically lean the mixture to the point of stalling the engine.
That miniscule + potential all it takes.


--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

I have not taken a position that there is not a requirement for reference air. I was questioning the design of using "through the wire".

Other designs may still take their reference air from through the wire, but per Walker Products Engineering, they chose a different design.

Question: "For my application, does the Walker Universal O2 sensor (250-23000) draw ambient air as a reference value or not. I am being advised not to solder the wires because they have to breath to allow reference air to get to the inside of the O2 sensor."

Answer: "All zirconia-based oxygen sensors require oxygen at their air reference. Many of the older sensor designs had no provision to "breathe" to the outside air, so they did indeed breathe through the wires, which was very ineffective. Newer sensors, including the Walker 3-wire design in the 250-23000, have a separate path to the outside air through Goretex materials that reject water droplets, but allow air to penetrate. This is much more effective."

As to the discussion of soldering, the Engineer added amplifying information to his earlier email: "In talking to my colleagues, they reminded me that the Walker sensor has a stainless steel wire core surrounded by a multi-stranded copper sheath. Soldering to this wire is difficult, while crimping is easy and effective. Before the crimping, remember to slide on the Walker-supplied shrink tubing, which is lined with a heat-curable epoxy that bonds to the wire insulation and makes a tight seal. It's good stuff."

I appreciated his followup as it was important to our discussion and wanted to share it with all concerned.

Received the Bosch full wire harness replacement today. Observations:
- the two heater wires are quite tightly seated into the body of the sensor. Nothing can pass through there.
- the sensor wire passes into the sensor differently. There appears to be material around the wire as it goes into the body of the sensor. Maybe Bosch uses the same Gortex technique and that is its design.
- about 12" up the wiring harness from the sensor are two zip ties wrapped tightly around outer cover about 4-6" apart. Feeling around it without compromising the cover, it feels like wires have been spliced. Can't tell which method, but my guess is its self sealing crimps. You can see a picture of it at the FCP Groton website.

This has been a good exchange and hopefully folks who go down this path in the future will have more information with which to make a decision.

Cheers!

Hi JR,

What you posted from Walker about the Goretex was interesting. I've always considered that business about the reference air depending on the interstices within a stranded wire a bunch of malarkey, at least as much as the warnings against soldering (and thus filling those gaps) is concerned. It was too hard to believe the migration of O2 through the zirconia followed those wires all the way to the wiper motor. Apparently, it was grounded in fact, although as your fortunate reply from Walker indicates, a poor initial design.

I'm actually writing in response to your post about the heater not working. The fact you always measure 7 ohms indicates it does indeed work, but you're measuring it with the exhaust system warm. Yes, I've done it. Try checking the resistance using a jumper to supply battery to the heater (fuse 4 if we're discussing a 240 here) without running the motor. Just let it heat up for a minute, then pull the plug and quickly measure to see the resistance fall through the temperature range without the external influence of a hot exhaust.
--
Art Benstein near Baltimore

I wonder if other dogs think poodles are members of a weird religious cult.
-Rita Rudner

I will admit I know little about the physics/chemistry of soldering, but.... wires breathe???

Randy

Buy the Bosch for a '90 Ford Escort, cut the wires & splice.
$40.

Have you done this and are you suggesting that it would work for a b230ft?

I have a 94 944T that runs great but appears to run rich based on the tailpipe residue. It was not the recipent of a lot of love before I got it and at 175K might very well be running with the original O2 sensor.

Thanks,

Randy

Yes, I have done it several times.

Great, thanks for the valuable information.

Randy