Splicing O2 Sensor Harness Connector

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MattC
Posts: 220
Joined: Jun 03, 2016 1:16 PM
Location: Bucks County, PA

Splicing O2 Sensor Harness Connector

Post by MattC »

Hey guys,

The harness connector for my O2 sensor completely disintegrated. I have another one with pigtail that could be spliced in. Looking for some collective wisdom here...is this a bad idea?

On a related note, I am switching my 533 to the 535 exhaust system which may result in my O2 sensor wire coming up short. Splicing this extra length at the harness might kill 2 birds w/ one stone.

If safe to do it, would the preferred method be soldering or using a Posi-Tap? Looks to be stranded copper wire.

Thanks, Matt

Currently:
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Here's a picture of the possible replacement:
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Mike W.
Posts: 26872
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Splicing O2 Sensor Harness Connector

Post by Mike W. »

Splicing it is not a bad idea. A big of a PITA since the green is a shielded wire, but your existing one almost looks like it could be shorting the shielding to the signal wire. Why it's shielded I have no idea since it's not from the O2 sensor to the connector, but it is. The wire from the O2 to the connector is a high temp, teflon I believe wire given it's proximity to the exhaust, so a generic wire isn't a good idea there, but the length of it shouldn't be a problem. One thing of note is the 535 O2 sensor is a heated one and the 533 is not, it's a single wire. You can substitute a heated for a non heated, but not the other way around, although single wire is all you need with a 533.
MattC
Posts: 220
Joined: Jun 03, 2016 1:16 PM
Location: Bucks County, PA

Re: Splicing O2 Sensor Harness Connector

Post by MattC »

Thanks Mike! So, plan will be to splice the new connector by soldering. Just need to double check that soldering this type of wire is Ok. Then I'll keep my existing single wire O2 sensor, assuming it has enough length. I understand an effect may be that it'll take a little longer to heat up and go closed loop since it's new position is further downstream.

Note on the shielded wire: I did a little more research and found a plausible explanation. "Shielding is only needed where O2 signal wire runs in a bundle to the ECU with the injector wires in parallel. The current pulses in the injector wires can induce current in the O2 signal wire and overwhelm the low voltage signal."

This would explain why the O2 sensor wire itself is not shielded, only the harness side.
demetk
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Joined: Aug 09, 2007 8:58 AM
Location: CT, USA

Re: Splicing O2 Sensor Harness Connector

Post by demetk »

Further downstream means the single wire sensor will more likely go offline at idle because of the lower exhaust temps. If you don't mind that then it's fine but if you do then you should get a 3 or 4 wire O2 sensor and retrofit it.
MattC
Posts: 220
Joined: Jun 03, 2016 1:16 PM
Location: Bucks County, PA

Re: Splicing O2 Sensor Harness Connector

Post by MattC »

demetk wrote: Jun 13, 2021 4:03 PM Further downstream means the single wire sensor will more likely go offline at idle because of the lower exhaust temps. If you don't mind that then it's fine but if you do then you should get a 3 or 4 wire O2 sensor and retrofit it.
Hi Jim, thanks for the input. It sounds like you're saying that, at idle, the exhaust temperatures cool down enough to force the O2 sensor circuit open loop, unless heated? Am I correct?

If I have my idle A/F ratio dialed-in properly (per your tutorial on AFM adjustment), then should the O2 sensor going "offline" at idle be a concern?

Meanwhile, I'll research a 3-wire retrofit.
demetk
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Joined: Aug 09, 2007 8:58 AM
Location: CT, USA

Re: Splicing O2 Sensor Harness Connector

Post by demetk »

If you have your AFM dialed in right then it shouldn't be a concern.

For a 3-wire retrofit you can use a 4-pin relay and use the fuel pump's pin 87 as the trigger just like the 87 535 does. 3-wire O2 sensor diagram I drew up.

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MattC
Posts: 220
Joined: Jun 03, 2016 1:16 PM
Location: Bucks County, PA

Re: Splicing O2 Sensor Harness Connector

Post by MattC »

demetk wrote: Jun 13, 2021 6:37 PM If you have your AFM dialed in right then it shouldn't be a concern.

For a 3-wire retrofit you can use a 4-pin relay and use the fuel pump's pin 87 as the trigger just like the 87 535 does. 3-wire O2 sensor diagram I drew up.
Perfect, thank you!
Mike W.
Posts: 26872
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Splicing O2 Sensor Harness Connector

Post by Mike W. »

demetk wrote: Jun 13, 2021 4:03 PM Further downstream means the single wire sensor will more likely go offline at idle because of the lower exhaust temps. If you don't mind that then it's fine but if you do then you should get a 3 or 4 wire O2 sensor and retrofit it.
Good point, I didn't think about that. I even retrofitted a 3 wire to a 733 one time though I don't recall the exact reason now or if it did what I was trying to get it to do.

One note on soldering, I believe the lead from the O2 sensor is stainless, so you can't solder it, but I think you're just referring to the body side which would be copper.
MattC
Posts: 220
Joined: Jun 03, 2016 1:16 PM
Location: Bucks County, PA

Re: Splicing O2 Sensor Harness Connector

Post by MattC »

Mike W. wrote: Jun 13, 2021 11:20 PM
One note on soldering, I believe the lead from the O2 sensor is stainless, so you can't solder it, but I think you're just referring to the body side which would be copper.
Hi Mike,
Correct, I'm only considering soldering the harness side. Like you said, just stranded copper wire. Everything I've read says the sensor wire itself should not be soldered, but not much out there about the harness wire. I can't think of any reason it would be a problem.

Also, I'm thinking it's unnecessary to connect the shield (because this new leg of wire will exist outside the wire bundle), but it can be done. I'd have to pay close attention to insulating between the signal and shield wiring since they are coaxial.
MattC
Posts: 220
Joined: Jun 03, 2016 1:16 PM
Location: Bucks County, PA

Re: Splicing O2 Sensor Harness Connector

Post by MattC »

Just a quick update for posterity...the job is done.

-Replacement connector soldered in.
-Electrical tape used to insulate the soldered joint.
-Overlayed the stranded shield wire, overlapping from both sides.
-Electrical tape used to tightly wrap this layer.
-Finished off with heat shrink tubing.

Now, hopefully everything works!

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MattC
Posts: 220
Joined: Jun 03, 2016 1:16 PM
Location: Bucks County, PA

Multimeter setting

Post by MattC »

Disclaimer: yes, I'm an idiot. It was 105 degrees in the garage and my brain wasn't fully functional.

So, I was just verifying closed loop signal from O2 sensor, but mistakenly had multimeter set for resistance, not voltage. :oops:

Anyone think this could've done any harm to the ECU? Obviously, my concern is the small amount of current put out by the MM when set to measure ohms. (note: I've observed no changes to the way the car runs).
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