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Old 04-18-2021, 10:09 PM   #1
WRXXXED
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Default P0139 help (slow rear o2 sensor response)

So I posted a thread talking about my journey in tying to fix this issue but to no avail. I've tried different sensors, searching and fixing exhaust leaks, etc. I don't have any oxygen sensor spacer to get rid of a cat code. I have a access port tune but I have another thing that I'm thinking is causing it.

So I had recently rebuilt the motor thats stronger (closed deck, I-beams, the whole thing). I went with higher CR pistons (from CP 8.2CR to a Wiseco 9.0 CR prison, same diameter pistons and same length rods)

Now my question is, would a higher compression piston affect the response? I'm not versed in tuning whatsoever so I'm just asking for opinions. If not could my tuner use the acessport to just turn off that code? My AFRs are looking normal across the board but I just don't understand what could be causing this slow response code after trying for weeks...
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Old 04-19-2021, 07:50 AM   #2
Elbert Bass
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What does your tuner say? Generally when someone tunes your car they should deal with any issues that pop up.
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Old 04-19-2021, 07:59 AM   #3
WRXXXED
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Quote:
Originally Posted by Elbert Bass View Post
What does your tuner say? Generally when someone tunes your car they should deal with any issues that pop up.
Hello again Elbert, I haven't contacted my tuner because I thought it was a mechanical issue. The tune was done in Aug of 2018 and nothing has changed or popped up from my engine until I finished the motor build in October of 2020. Even before I started the build the light hasn't popped up. The only thing I can think of that has changed with the build is a higher CR but I don't know if that would effect it. I'll give the shop a call today and find out if they think that could cause any problems
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Old 04-19-2021, 10:10 AM   #4
benflynn
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I feel ya, I just installed an engine now my immobilizer is out of sync, and I had a muffler shop kill an ecu once pulling an o2 and letting the wires ground.
Iíd delete it.
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Old 04-19-2021, 10:29 AM   #5
WRXXXED
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Called the shop, they said that they would not delete the code for me and that my best bet would be to weld in a high flow cat. Anyone know a place in PA that would delete JUST the slow response code? I don't want to get rid of my oxygen sensor, just the slow response for it. I am just so stumped and getting annoyed with it. The last thing I want to do is throw money at it welding in a high flow cat and still have it pop up
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Old 04-20-2021, 03:11 PM   #6
benflynn
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With epa out and about, I doubt anyone will respond any differently to such a call. Times like this U need a personal relationship. EPA will have everyone on open source before long.
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Old 04-21-2021, 09:32 AM   #7
WRXXXED
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Quote:
Originally Posted by benflynn View Post
With epa out and about, I doubt anyone will respond any differently to such a call. Times like this U need a personal relationship. EPA will have everyone on open source before long.
Yeah, thats the problem I guess, I've been under the car while it is running, no exhaust leaks, guess ill try replacing the oxygen sensor harness and then if that doesn't work ill weld in a cat
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Old 04-21-2021, 08:50 PM   #8
benflynn
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I donít see the cat helping slow response. Someone capable of tuning that thing will chime in and delete that for you. Openport will do it, Iím sure u would need to tune it then, easy enough and you are no longer have to worry about Cobb
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Old 04-26-2021, 03:20 PM   #9
WRXXXED
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Holy cow do I have a weird thing going on with this rear oxygen sensor harness... so NASIOC won't let me upload pictures for some reason but here are the links:

https://ibb.co/BP5bmYf
https://ibb.co/qJ2LQbJ
https://ibb.co/jhCrYZW
https://ibb.co/6Wjwhkt
https://ibb.co/1nzD48D

So from what I can tell there are 2 heater wires, and then a ground and a signal wire. I've tried looking through threads and none of the colors are matching up with the harness I have. As well that I can't find any threads verifying that there is supposed to be a bridge between two of the wires.

For whatever reason 2 of the wires are bridged on the harness (Blue and White wires) and then the white wire also seems to be spliced into a bigger grey wire??? I don't know what kind of makeshift harness this is but its very weird.

Hopefully someone can shine some light on the situation, I have a new harness on the way
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Old 04-26-2021, 04:32 PM   #10
WRXXXED
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So I found a thread saying that the bridge between the wires and the grey wrapping is supposed to be there, back to square 1
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Old 04-26-2021, 08:05 PM   #11
Elbert Bass
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Quote:
Originally Posted by WRXXXED View Post
So I found a thread saying that the bridge between the wires and the grey wrapping is supposed to be there, back to square 1
The wire in the grey wrap is shielded but only the white color wire should connect to anything. Although the connection for the shield in the grey par is to ground, it grounds back at the ECM. Looks like your wires have melted together. That blue wire is a ground circuit but that connection could be creating a ground loop which can create electrical noise. I would snip that connection, and insulate those wires. Also make sure the center wire and the outer wire wrap in the grey are not shorted together
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Old 04-26-2021, 08:14 PM   #12
WRXXXED
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Okay so took a look at the FSM and through this page (https://ibb.co/G0SDT8Q) went through and I got the first and last checks done but could not get a reading for the connection between "rear oxygen sensor connector and chassis ground" the sub-harness is plugged into the engine harness but no ground that i would touch would give me a reading

First ohm: 0.2
Second ohm: 5.4

All within the specifications given

Last edited by WRXXXED; 04-26-2021 at 08:33 PM.
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Old 04-26-2021, 08:38 PM   #13
WRXXXED
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Quote:
Originally Posted by WRXXXED View Post
Okay so took a look at the FSM and through this page (https://ibb.co/G0SDT8Q) went through and I got the first and last checks done but could not get a reading for the connection between "rear oxygen sensor connector and chassis ground" the sub-harness is plugged into the engine harness but no ground that i would touch would give me a reading

First ohm: 0.2
Second ohm: 5.4

All within the specifications given
Okay so I did the second test now as I forgot to plug the ecu plug back in lol, and got a reading of 5.3 ohms, now the FSM called for at least 1 Megohm so I know that the ground in this oxygen sensor harness is bad. I have a new harness coming either tomorrow or Wednesday so ill be replacing that and then checking the resistance again! Very happy to have some good news
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Old 04-26-2021, 08:44 PM   #14
WRXXXED
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Quote:
Originally Posted by Elbert Bass View Post
The wire in the grey wrap is shielded but only the white color wire should connect to anything. Although the connection for the shield in the grey par is to ground, it grounds back at the ECM. Looks like your wires have melted together. That blue wire is a ground circuit but that connection could be creating a ground loop which can create electrical noise. I would snip that connection, and insulate those wires. Also make sure the center wire and the outer wire wrap in the grey are not shorted together
Hello Elbert, the white wire is connected to the blue wire intentionally as others harnesses are the same. When I took the factory electrical wrap off it appears that they put in some sort of black putty to help keep things in check because it was very sticky and felt like half dried glue or some sort of adhesive...

Here's a link to the thread I found explaining why they're connected:
https://forums.nasioc.com/forums/sho....php?t=2909633
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Old 04-29-2021, 01:08 PM   #15
WRXXXED
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Okay so installed the new oxygen sensor harness and took another ohm reading and its still the same. When I started the car the code cleared but I believe thats just because the connection was broken. Going to see if the code comes back and if it does I guess there's a short from the ECU to the connection that I plug the harness into. Well see...
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Old 04-30-2021, 09:52 PM   #16
WRXXXED
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Sure enough, popped up again
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Old 05-09-2021, 08:48 PM   #17
WRXXXED
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Truly not sure what caused it but had a member on here who helped me out in fixing the problem and will be getting a tune from them soon to completely fix the problem
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