4 wire Oxygen sensor installed

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Legacy777
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4 wire Oxygen sensor installed

Post by Legacy777 »

Here's reference post....for those that haven't read it.
http://bbs.legacycentral.org/viewtopic. ... ensors+com


I just installed this last night, and lemme say....wow.....I don't think my car has ever idled as good as it does now!! Idle is pretty much rock solid. There seems to be a little more power/smoothness in the mid-range rpms. Hopefully my mpg will increase as well. Just have to wait and find out.

Re the sensor itself, it's a good unit, the only thing that was crap was the generic directions. They are incorrect in terms of what wire to hook up to what. So if anyone does this mod, don't use their directions. I'll have to double check, but I believe that the white wire on the OEM sensor is the actual sensor wire. The red & black are the power & ground wires.

For 50 bucks, this was a nice upgrade. I messed up during install and forgot to put the shrink wrap sleeves on one of the wires, so I had to cut it off, then redo it, but I had to add an extra piece of wire in there because it was too short......it was a mess.....anyway....make sure you have the shrink wrap on the wire before you do your final crimp.....or you'll be SOL.
Josh

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Post by vrg3 »

That's great that you saw such an improvement. How old was the 3-wire sensor you took out? I'm wondering if we should attribute all the improvement to just the separate ground.

Where did you connect the sensor ground wire? Did you use -K-'s idea and just use the heater ground?

Just to note, the wire colors are different on the harness side and the sensor side of the connector.

You're right -- on the sensor side, white is signal, black is heater ground, and red is heater +12v. Technically the heater isn't polarity-sensitive, I think, but that's how it's wired. On the harness side, white is signal again, black-with-white-stripe is heater ground, and yellow-with-red-stripe is heater +12v.
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Post by entirelyturbo »

Okay. This sounds like something I want to take a swing at. However, let me see if I gathered this correctly from the other thread, we all know I'm not the electric whiz around here ;)

I will remove my old sensor, steal the connector off of it, and splice the connector onto the corresponding 3 wires on the new O2 sensor. Therefore it will plug right into the wiring harness. Then I will find a way to attach the 4th wire (the ground wire) to the body somewhere nearby, effectively giving a better ground, and hopefully a more accurate sensor.

Is that the way of it?
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Post by vrg3 »

I would recommend splicing the 4th wire (sensor ground) together with the heater ground wire that's already on the harness. The heater ground does go to the ECU. But, yes, what you wrote seems correct; Josh can clarify.
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Post by Legacy777 »

The sensor I pulled out I put in around 121k miles, sept-oct 98. I currently have 174k miles.

It's possible the sensor was getting lazy......but after seeing how rusted the head bolts were and everything.....I'm sure it wasn't getting the best ground.

I connected the sensor ground to the heater ground. It goes to the ECU, as good as place as any for it to go.

Yes wire colors are different on engine side........the heater is not polarity sensitive.....instructions even say so.

subyluvr, if you do this, make sure you leave yourself some extra wire length in the event you do a boo boo like I did, and make sure you have the shrink wrap on.....and splice the sensor ground with the heater ground.
Josh

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Post by entirelyturbo »

Okay so the wire colors on my old sensor and the one I'm going to buy are the same? Meaning splicing them together will be easy as far as identification goes?

Except for the heater ground, which (on the wiring harness) is a different color wire than the sensor? I am bypassing the plug when I wire in the heater ground sensor to the wiring harness, right? What colors am I looking for here? Josh, I'll buy the same sensor that you bought for simplicity...

Also, Josh, after a tank or two of gas, can you report back and tell us how your mileage has changed?
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Post by Legacy777 »

The colors on the 4-wire sensor are not the same, however they are labeled on the instructions. The colors are like blue, white, & black....or something of that nature.

I wrote down the color coding on the directions.....I'll post them when I get home tonight.

You are not bypassing anything. You're hooking both ground wires together. I'll post the little color coding thing....that might help......if not...email or IM me.....and I'll try to explain it.


I'll keep ya posted on the mpg too.
Josh

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Post by Legacy777 »

Ok, here's what the wires are & what you connect what to what.

OEM O2 sensor wires

Black = Heater Ground

Red = Heater 12v+

White = O2 Sensor


Walker Generic 4-wire O2 sensor wires

Blue = O2 Sensor

White = Sensor Ground

Black = Heater Ground

Black = Heater 12v+


Since the heater is not polarity dependent, it doesn't matter which black wire you use at ground and 12v+.

When you hook things up

Hook OEM white wire to Walker blue wire

Hook OEM red wire to one of the Walker black wires

Hook OEM black wire to Walker's white & other black wire.

questions?
Josh

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Post by vrg3 »

Nice concise color-coded instructions. :) For clarity's sake -- you cut the connector off of the stock sensor and spliced it in with the Walker sensor, discarding the stock sensor itself, correct?
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Post by entirelyturbo »

Sweet! :twisted:

Awesome instructions, Josh. Makes perfect sense.... I'll get a sensor soon, and VERY soon since I just measured my mileage for a 250-mile trip, nothing but highway... 24 mpg... terrible... :oops:
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Post by JasonGrahn »

maybe i'm not seeing it, but what is the science behind WHY using a 4 wire instead of the OEM 3 wire is beneficial?
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Post by THAWA »

The extra wire is for grounding since a 3 wire sensor grounds through the body of the sensor itself which would be the exhaust manifold most of which are rusty. Correct me if I'm wrong.
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Post by entirelyturbo »

Right. My exhaust isn't all that terribly bad, kinda yucky-looking but not like it came from the bottom of the ocean :P However, grounding through the ECU will still probably provide a more accurate reading than through the exhaust...
2000 Subaru Legacy B4 RSK

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Post by Legacy777 »

vrg3 wrote:Nice concise color-coded instructions. :) For clarity's sake -- you cut the connector off of the stock sensor and spliced it in with the Walker sensor, discarding the stock sensor itself, correct?
correct.....I still kept the stock sensor, but it's not worth anything.
Josh

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Post by 123c »

If things work out with the 4 wire O2 Sensor, then I might consider doing it sometime. Right now my car is getting around 16mpg in the City, and about 23 on the highway, and I want to increase both of these numbers.
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Post by ciper »

So better late than never, during my vacation from the board I did the exact same thing. I too decided to run the ground for the sensor and heater back to the ecu together.

For the most part I agree with everything said so far, except the performance gains which I cant verify since other changes had been made to the car at the same time. I do know the car is better than before though and my old sensor was only 35k miles old!

For my turbo project I also plan to use a 4 wire sensor, except relocate farther down the DP that what is stock.
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Post by 123c »

Any updates on how this modification is working???
[color=red][b]1993 Subaru BC Turbo Legacy (193k miles)
1971 VW Super Beetle
1989 Honda Elite 50
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Post by Legacy777 »

Everything seems to be working very well. I don't really have many miles on the car, just because I live so close to work, and my mileage is also going to suck because of it too.......if I ever get a good highway mileage trip, I'll try and see how the mileage goes.
Josh

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Post by 123c »

Sounds good to me, I ordered the sensor last night, and should get it this week. I hope I will be getting better than 15mpg in the city now, and low 20s on the highway...
[color=red][b]1993 Subaru BC Turbo Legacy (193k miles)
1971 VW Super Beetle
1989 Honda Elite 50
[/color][/b]
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Post by 123c »

Does anyone know the tourque spec for tightening the O2 Sensor?
[color=red][b]1993 Subaru BC Turbo Legacy (193k miles)
1971 VW Super Beetle
1989 Honda Elite 50
[/color][/b]
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Post by Legacy777 »

tight....but not too tight ;)
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Post by 123c »

I don't need on of those special O2 sensor wrenches either do I? I can just use a 22mm box end wrench?
[color=red][b]1993 Subaru BC Turbo Legacy (193k miles)
1971 VW Super Beetle
1989 Honda Elite 50
[/color][/b]
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Post by Legacy777 »

I just used my crescent wrench, so yeah a box end wrench should work fine
Josh

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Post by 123c »

That's good to know, I will just use the big guy I use to change the fuel filters on the Mercedes :D
[color=red][b]1993 Subaru BC Turbo Legacy (193k miles)
1971 VW Super Beetle
1989 Honda Elite 50
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Post by 123c »

I got my Sensor in today, and I ended up using an O2 sensor wrench, since I couldn't get the Box end in there. I also found the tourque spec is 35 ft/lbs. I however didn't use my tourque wrench because I couldn't get it to fit. Should I worry about over-tightening it, since I got it in there very snug???
[color=red][b]1993 Subaru BC Turbo Legacy (193k miles)
1971 VW Super Beetle
1989 Honda Elite 50
[/color][/b]
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