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      11-24-2016, 10:41 PM   #1
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Exclamation Lean/Oxygen sensor trouble shooting (F-series N55)

Hi guys

The other day I had an incident where trims did not respond and my car went lean during a JB4 log. I was told this is because the car went into open-loop caused by a defect oxygen sensor. There was no CEL.
Now, how do I trouble shoot this? How to test if the oxygen sensor is defect and which one it is? I find it hard to believe that something so advanced as the F-series does not throw a code for a faulty O2 sensor?
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      11-24-2016, 10:42 PM   #2
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Admin. Please move to N55 Engine section - thanks.
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      11-25-2016, 12:38 AM   #3
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I hear that the Bosch 4.9 sensor should be a better version. Does anyone know if the 11787596924 or 11787596908 is is the 4.9 version, and why the length changes for the same model
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      11-26-2016, 07:32 AM   #4
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Quote:
Originally Posted by harkes View Post
I hear that the Bosch 4.9 sensor should be a better version. Does anyone know if the 11787596924 or 11787596908 is is the 4.9 version, and why the length changes for the same model
Different for different wastegate models which have different downpipe so as seen

Pre 7/2013
Post 7/2013
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      12-17-2016, 09:47 AM   #5
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A failed O2 would toss an CEL error.

You sure anything is actually wrong? It looks like it's doing a throttle cut at high RPM (tire slippage?)

Previously in life, EFI vehicles always went into open loop mode under hard acceleration since O2 sensors did a bad job of reading rich mixture. These cars run pretty lean under load in comparison, so I don't know if the O2 is used for acceleration as well.
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      12-19-2016, 09:15 PM   #6
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Quote:
Originally Posted by Wires View Post
A failed O2 would toss an CEL error.

You sure anything is actually wrong? It looks like it's doing a throttle cut at high RPM (tire slippage?)

Previously in life, EFI vehicles always went into open loop mode under hard acceleration since O2 sensors did a bad job of reading rich mixture. These cars run pretty lean under load in comparison, so I don't know if the O2 is used for acceleration as well.
Correct but the N55 is running closed loop - also under WOT.

I have ordered a new O2 sensor - will report if itsolve the problem.
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      12-20-2016, 07:04 PM   #7
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Thanks for the insight. I was wondering about that considering the AFR they run under load.

If you hook up an ODB2 diagnostic tool you should be able to watch the O2 readings. They are cyclical (go a little to rich and then back to lean) in a sine pattern. If a sensor is bad, then it won't follow that pattern.
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      12-21-2016, 08:15 PM   #8
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I forgot to mention if you had a rich misfire, it will show up lean on the logs as well. Raw fuel in the exhaust is high in oxygen and can give a false positive lean reading.
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      06-03-2023, 05:54 PM   #9
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Quote:
Originally Posted by harkes View Post
Correct but the N55 is running closed loop - also under WOT.

I have ordered a new O2 sensor - will report if itsolve the problem.
hey Harkes,

I have the exact same issue as you but on the B58 platform, did the o2 sensor solve your issues? sorry for reviving the dead thread but I can't figure out what the issue is.

If the sensor did not fix it, do you know what did?

hope to hear from you!

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      06-04-2023, 01:40 AM   #10
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Quote:
Originally Posted by NLR View Post
hey Harkes,

I have the exact same issue as you but on the B58 platform, did the o2 sensor solve your issues? sorry for reviving the dead thread but I can't figure out what the issue is.

If the sensor did not fix it, do you know what did?

hope to hear from you!

Damn... Loooong time ago. Don't remember ever getting it fixed. Just didn't have the problem after binning the JB4
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      06-06-2023, 04:59 AM   #11
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Quote:
Originally Posted by M-terkait View Post
Different for different wastegate models which have different downpipe so as seen

Pre 7/2013
Post 7/2013
if I used older sensors on newer wastegate car, could that cause running rich?
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