Expirimental Oxygen Sensor Swap

[mzarifkar]

I mentioned earlier that i had a 1221 code, and was going to replace the oxygen sensor.

My dad's company recently got a lot of Bosch sensors back for warannty reasons or something and since they were going to throw them away anyway after testing. He managed to get me one. This new sensor had a different tip, as in 3-4 little holes in it as opposed to the slits that were on the old one, besides that, same dimensions and outputs wires. the only corrospondence between the two numerically was a 3 digit number, i thik 382 or something, and 12volts. It had a different connector, but since the wires were too short anyway i extended them with the old wires and connector harness.
sensor replacement was a PITA, the sensor tool i had was the long kind, so i had to remove the heatshield abovethe cats and mufflers toget more clearance.
Put the sensor in, started up, had a rough idle, i think because the computer was learning the new parameters from this sensor, went for a mile drive, came back, idled fine.
rebooted computer per battery disconnect, upon startup smooth idle, no check engine light, no codes. took her out for a drive to compare to old sensor performance and all seemed the same at 40 and 80 mph for fuel consumption, acceleration maybe a tad better, but it may be placebo and or a cold transmission too.

I have sofar put about 10 miles onthis sensor, without any check engine light, or codes. It takes about 30miles for it [ CE Light] to come on after a reboot if it is going to so im crossing my fingers and the money saved by using a generic sensor can go to pay the vet's boat payments as our guinea pig is ailing.

I will update as to the results once i get more miles if it works ill try to get some specs on these sensors for the frugal e34-ers out there

-eM

[genphreak]

I believe any 3-wire Bosch will work, the main thing to be sure of is the soldering is good (they use silver wires in the cable and good insulation to cope with the intense heat). I doubt the different holes mean much. But perhaps if it was in a batch decalred faulty it could have an incorrect output? It'd pay you to hook up a multimeter inside the car, with some wires run out to the sensor connector so you check it's output whilst driving. After that do the same with your ICV and AFM, you want to know how they compare to OE spec too. All the specs are in the Bently or are searchable online. We'd love to know how it stands up to an empirical test too ... Nick

[mzarifkar]

This is actually a 4 wire sensor, as was the one coming out.
I made my connection at a distance from the wire where it will be away from both engine and exhaust heat, then doubled up on its heat insulation.
As for empirical data, in my wishfull mindset i installed it all in and gaining acces to the connected is a pita to hook it up to a meter. so unless it doesnt work, i hope to never see that thing again

The sensor was part of a batch that had a faulty sensor in it, and appearantly they send them all back if this is the case. mine was tested and passed, even though it was used (because it was tested) it has no actual mileage or anything on it, so basically new.

I figured the car is smart enough to adjust to whatever range of output the sensor gives. and after resetting the computer the car has run fine. today ill put some miles on it and we'll see!

[genphreak]

The car does not adjust any, it simply expects a particular impedance which the sensor is (supposed to provide) depending on the gas it is measuring. 4 wire ones are wide band sensors and are different to 3 wire- I guess you can just use the right sensor wire and be done wiht it as you have.

Re your solder joint, just remember how much heat it takes to melt lead and compare that to how hot a cat can get (600F). All that heat can travel down the wire a long way on a hot day when the car is in traffic... so you must make sure the joint is (also) physically strong.

EDIT: I am wrong re 4-wire, note Winfred's post below. Some are narrow band like 3-wire ones. Only sensors designed for OBDII compliant vehicles/applications are the wide band ones.

[mzarifkar]

So far after 35 miles no check engine lights come on yet, so thats good. I have long drive next weekend, after that i will re evauluate my solder joint. I staggered the wires when i cut thems so theyre not all soldered at one place, and i kind of braided the wires together (not twist) before soldering. In a month i have a 800mile trip which would be the ulitmate test.

I never considered the thermal conductivity of the wire itself inside of it. i was thinking that by slapping on extra insulator from the old wire, and having it "in the wind" it would help cool, but i think the extra insulation will jsut keep it warm and actually decrease the cooling that the wind will have on it.

[winfred]

the early 4 wire sensors are just like a 3 wire sensor but with a ground wire (gray wire) instead of depending on the exhaust for being a good ground, they operate in the same range 0-1 volt, the obdII cars run a 0-5 volt sensor

[genphreak]

I never considered the thermal conductivity of the wire itself inside of it. i was thinking that by slapping on extra insulator from the old wire, and having it "in the wind" it would help cool, but i think the extra insulation will jsut keep it warm and actually decrease the cooling that the wind will have on it.

The heat is why they use silver wires, not copper.

Cu would oxidise and crap out after a year or three. Same can go for a soldered joint too near the cat- tho most people get away with it like this for a while. I think key issue here is also to prevent the ingress of water from the road. PVC tape would eb no good of course, a really decent length of heat shrink would be the minimum I'd use over a joint down there.

Thanks for the 4-wire correction Winfred. I'm glad I still get to feel like a n00b, it underscores one of the extradordinary virtues of bimmer.info