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Discussion Starter #1
Which O2 sensor (pre-cat or post-cat) measurement has a direct impact on engine performance in the S62?

Thanks.

Jeff cherrsagai
 

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x703jko said:
Which O2 sensor (pre-cat or post-cat) measurement has a direct impact on engine performance in the S62?

Thanks.

Jeff cherrsagai
Well, since I have a 50/50 shot at getting it right :M5thumbs: , I would guess the precat. The post cat O2 measure the difference, and if it is outside the specified range, SES lights. That is why an O2 simulator post cat on racing cats solves the SES llight problem.
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Jerry
 

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Discussion Starter #3
gsfent said:
Well, since I have a 50/50 shot at getting it right :M5thumbs: , I would guess the precat. The post cat O2 measure the difference, and if it is outside the specified range, SES lights. That is why an O2 simulator post cat on racing cats solves the SES llight problem.
Regards,
Jerry
Thanks Jerry. Anyone else? Jeff cherrsagai
 

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i would agree with Jerry on this one...most everything i know, would lead me to believe that the most important is the first one as that is the one that is supposed to directly measure the output from the engine and then the post cat is supposed to check that against what should be comming out from the cats
 

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Discussion Starter #5
SC'dKellenersM5 said:
i would agree with Jerry on this one...most everything i know, would lead me to believe that the most important is the first one as that is the one that is supposed to directly measure the output from the engine and then the post cat is supposed to check that against what should be comming out from the cats
Thanks. Next question everyone. How would a faulty pre-cat O2 sensor affect performance? What would the symptoms be?

Jeff cherrsagai
 

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depends on how the sensor is faulting..the car could be running rich or lean. So you could be loosing power or loosing power and may have a bad situation in the lean condition.
 

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SC'dKellenersM5 said:
depends on how the sensor is faulting..the car could be running rich or lean. So you could be loosing power or loosing power and may have a bad situation in the lean condition.
Exactly. One way to check is pull the plugs and see how they look. If they are dark, you are running rich. Also remember that the O2 sensor should be deactiviated at WOT, as the car should go full rich per whatever the ECU programming is. Are you having any symptoms? Most cars exhibit noticable reduction in gas mileage (too rich). O2's last anywhere between 30k and 60k, I did have one swapped out under warranty/maintenance at 26 or 27k.
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Jerry
 

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Discussion Starter #8
gsfent said:
Exactly. One way to check is pull the plugs and see how they look. If they are dark, you are running rich. Also remember that the O2 sensor should be deactiviated at WOT, as the car should go full rich per whatever the ECU programming is. Are you having any symptoms? Most cars exhibit noticable reduction in gas mileage (too rich). O2's last anywhere between 30k and 60k, I did have one swapped out under warranty/maintenance at 26 or 27k.
Regards,
Jerry
No, I'm just curious.

I do, however, continue getting nuisance cat efficiency faults on the driver's side cat. It was replaced about 8000 miles ago in an attempt to eliminate the problem, but I keep getting codes - about every two weeks.

There's no noticeable change in performance...just the code.

Jeff :cheers:
 

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x703jko said:
No, I'm just curious.

I do, however, continue getting nuisance cat efficiency faults on the driver's side cat. It was replaced about 8000 miles ago in an attempt to eliminate the problem, but I keep getting codes - about every two weeks.

There's no noticeable change in performance...just the code.

Jeff :cheers:
If you think O2 sensor is bad, swap left and right and see if the code changes sides. If so, points to bad O2. If not, look elsewhere.
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Jerry
 

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Discussion Starter #10
gsfent said:
If you think O2 sensor is bad, swap left and right and see if the code changes sides. If so, points to bad O2. If not, look elsewhere.
Regards,
Jerry
Jerry. Thanks for the advice. I'm going to either do what you've suggested or have them replace both pre-cat sensors (my nickel of course).

I'll let you know what happens.

Jeff :cheers:
 

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Definitely the pre-cat sensor. Post cat sensors have NO effect on engine management and only serve to give feedback with regards to catalytic efficiency.

:cheers:
 

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not sure if this was already said, but you may have a bad post cat 02 sensor, the precat sensor should not be causing a cat efficiency code, but it the post cat sensor was bad, it could.
Mike
 

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Jeff...

Sorry, I missed the bit about cat eff. codes, so Mike is right. Efficiency codes are a result of the POST cat sensors as I noted above. I had codes from both sensors after installing the Supersprint headers and racing cats onto my existing x-pipe and SS mufflers.

I finally fixed this with a dual output O2 sensor simulator from www.o2simulator.com and have not had an SES light for cat efficiency since. If you want to go this route, Ben has posted the DME wires to use on the bmwtips website.

:cheers:
 

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Discussion Starter #14
mottati said:
not sure if this was already said, but you may have a bad post cat 02 sensor, the precat sensor should not be causing a cat efficiency code, but it the post cat sensor was bad, it could.
Mike
Mike. Thanks for the info. I suggested to BMW that they replace the post cat sensor on the bank that failed but for some reason, they (BMW/Dinan) decided to replace the cat instead. I would have thought that the sensor replacement was cheaper, but...

Anyway, I'm going to press them on this, but since the code is sporadic, I doubt that they'll replace it under warranty.

Jeff cherrsagai
 
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