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Old 12-23-2017, 02:05 PM   #1
RenaissanceMan
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UGH. Can't figure out what is throwing these O2 sensor codes.

Just finished my S52 OBD2 swap and the car is running fantastic, but after about 10 or so miles of driving, I will get O2 sensor adaptation limit and out of range faults on both banks. From what I've read up here in different threads, that is usually caused by one of 3 things:

-vacuum leaks
-dying MAF
-bad CVV

I should also add that I am only running the 2 O2 sensors pre-cat on my headers, and had the post cat sensors flashed out when my ECU was flashed.

I have changed the MAF with no result. I've also checked for vacuum leaks by spraying starting fluid everywhere I can find a potential vacuum breach but I'm not getting any change in idle. I haven't changed the CVV yet but I would have thought it would be a vacuum leak candidate if it was bad.

Anyone have any insight or other ideas? I'm tearing my hair out over here. Thanks-
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Old 12-27-2017, 08:33 AM   #2
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Anyone have any ideas?

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Old 12-27-2017, 08:53 AM   #3
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You have probably mixed the front and rear o2 connectors. Try swapping them.
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Old 12-27-2017, 12:05 PM   #4
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What are your fuel trims doing? Any way you get get data logs?
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Old 12-27-2017, 12:53 PM   #5
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Quote:
Originally Posted by pazi88 View Post
You have probably mixed the front and rear o2 connectors. Try swapping them.
99.9% sure I have the connectors properly connected, but I will double-check.

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What are your fuel trims doing? Any way you get get data logs?
Yes, I will be able to as soon as my OBD2 adapter cable arrives in the mail in a couple of days. I have software to monitor, but I needed an adapter to connect to the round OBD connector that came from the swap.... Until then, I'm only able to read codes from my Peake reader.
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Old 12-27-2017, 02:49 PM   #6
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Possible fuel pressure issue or feed/return lines backwards?
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Old 12-27-2017, 03:09 PM   #7
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Possible fuel pressure issue or feed/return lines backwards?
I'm using an e39 fuel rail with built in FPR. I have the return coming from the FPR side and the send going to the other. If I had a fuel pressure issue would the car run as well as it does under WOT? Not having any running problems at this point.

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Old 12-27-2017, 04:00 PM   #8
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Old 12-27-2017, 04:01 PM   #9
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I don’t have enough experience with e36 to comment on the wot but an e46 can be running fine and the light will trigger under the slightest lean condition. They are very sensitive of any unmetered air or not enough fuel. You really need to smoke test for a vacuum leak as it could be anywhere in the crankcase and wouldn’t necessarily bump the idle with ether.
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Old 12-28-2017, 04:28 AM   #10
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99.9% sure I have the connectors properly connected, but I will double-check.
Front connector goes to rear header lambda and vice versa.
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Old 12-28-2017, 11:14 AM   #11
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Yeah the connectors for the O2 sensors above the intake/fuel rail are sort of 'backwards'. That certainly contributed to some of the fuel trim issues I was having post-swap. Did you use new O2 sensors?
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Old 12-28-2017, 11:41 AM   #12
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Yeah the connectors for the O2 sensors above the intake/fuel rail are sort of 'backwards'. That certainly contributed to some of the fuel trim issues I was having post-swap. Did you use new O2 sensors?
Then I definitely need to check that. In my ignorance I assumed the position didn't matter to the computer since they were the same type of o2 sensor. I didn't buy new sensors yet... The motor had 88k on it. Maybe I should just to eliminate any issues with those.

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Old 12-28-2017, 05:03 PM   #13
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Oh it definitely matters lol. I learned the hard way and I've got a thread on here with the fuel trim logs to prove it!

As pazi above says - the rear O2 connects to the 'front' connector near the fuel rail, and the front O2 sensor connects to the 'rear' connector. I know clearance at the firewall is tight, but I would try to confirm the sensors are connected in the correct order before throwing more parts at it. It's a bit of a PITA to get to the sensors and route the wiring with the engine in the car.
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Old 12-28-2017, 06:54 PM   #14
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Quote:
Originally Posted by pazi88 View Post
You have probably mixed the front and rear o2 connectors. Try swapping them.
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Oh it definitely matters lol. I learned the hard way and I've got a thread on here with the fuel trim logs to prove it!

As pazi above says - the rear O2 connects to the 'front' connector near the fuel rail, and the front O2 sensor connects to the 'rear' connector. I know clearance at the firewall is tight, but I would try to confirm the sensors are connected in the correct order before throwing more parts at it. It's a bit of a PITA to get to the sensors and route the wiring with the engine in the car.
Thanks for the headsup! So just to be clear, when you are referring to 'front' and 'rear' positions, you are talking about the relative positions of the upstream sensors at the headers, correct?
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Old 12-28-2017, 09:31 PM   #15
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Yes. Basically - the sensors are sold with the same length of cable to the harness connections on top of the engine. So - since the front sensor is 'more' forward at the header, its connection is the rearmost on top of the engine. And since the rear sensor is further back, there is more slack in the wiring, so its connection is in the front.
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