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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > running bad O2 sensors hurt the engine?



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      10-19-2012, 09:46 AM   #1
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Exclamation running bad O2 sensors hurt the engine?

Over-arching question: Is it bad to drive an N54 aggressively or as a daily driver with bad O2 sensors? My car is FBO with catless DPs.

A little more context: I've been having difficulty maxing out fuel trims on pump gas maps (or with E85 maps) under WOT when I log. I stopped running E85 for this reason and figured it was just the stock fueling limits on the DME so I switched back to just 93 and was consterned to find that I'm still maxing out trims even when I drop down to stage 2 of the aggressive 9-10 maps at 100% OL fueling.

I'm also getting the following codes:
11314
11371
10720
10721 (these last two are showing up even with 100% 93 oct)

The first two are related to O2 sensors. I was told that I'm maxing out fuel trims possibly due to the O2 sensors being bad. But I thought that under full load our cars switch to CL fueling and thus ignore the O2 sensors entirely. So wouldn't that obviate the possibility that the O2 sensors could cause you to lean out at WOT? Wouldn't it be more likely injectors or fuel pump issues, not that I'm throwing codes for the latter?

Any suggestions would be appreciated. The sensors are $150 bucks a piece so I don't want to spend $600 plus labor if I don't have to right now. I've attached a log for your viewing pleasure...this was a quarter mile run from the other night...stage 2 with 100% OL fueling.
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      10-19-2012, 09:49 AM   #2
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Damn I have never seen fuel trims that are pegged at max...Just dont run the car hard and you should be okay for the time being until you swap them out..
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      10-19-2012, 09:50 AM   #3
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Quote:
Originally Posted by cn555ic View Post
Damn I have never seen fuel trims that are pegged at max...Just dont run the car hard and you should be okay for the time being until you swap them out..
I guess you can see the logs I posted? They're not showing up for me LOL. Anyways, does that make sense that the O2 sensors could cause that?
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      10-19-2012, 09:55 AM   #4
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would help and speed up responses if you could actually post the real codes and what it means.
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      10-19-2012, 10:02 AM   #5
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sorry, here they are:

2C32 (lambda probe in front of cat 2, trimming control)
2C6B (lambda probe behind catalytic converter, sys check)
29E0 and 29E1 (fuel mixture control 1&2)
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      10-19-2012, 11:16 AM   #6
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It is VERY important to have working primary o2 sensors on this car.

I'm curious if you noticed a drop in gas mileage, smell of fuel, or excessive black soot out your exhaust?

Most cars and I say most hesitantly will run in a "safe mode" where it basically dumps fuel for safety when the o2 sensors are not working. I'm not sure if this car works in such a fashion but would never drive this car tuned without a working o2 sensor. That is the life line of the engine.

The secondary o2 sensor behind the cat isn't as important as that just reads cat efficiency. It's quite uncommon to have all the o2 sensors go. However, the are sensitive to vibrations and dropping and repeated install/uninstall.

I do not recommend paying for labor on an o2 sensor replacement (if you are on a budget) as the job is pretty straight forward, unplug them and remove with a simple spark plug tool or open ended wrench. Getting to them is not the easiest but it should only take about an hour tops to do it yourself in the driveway.
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      10-19-2012, 11:38 AM   #7
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Quote:
Originally Posted by Jeff@topgearsolutions View Post
It is VERY important to have working primary o2 sensors on this car.

I'm curious if you noticed a drop in gas mileage, smell of fuel, or excessive black soot out your exhaust?

Most cars and I say most hesitantly will run in a "safe mode" where it basically dumps fuel for safety when the o2 sensors are not working. I'm not sure if this car works in such a fashion but would never drive this car tuned without a working o2 sensor. That is the life line of the engine.

The secondary o2 sensor behind the cat isn't as important as that just reads cat efficiency. It's quite uncommon to have all the o2 sensors go. However, the are sensitive to vibrations and dropping and repeated install/uninstall.

I do not recommend paying for labor on an o2 sensor replacement (if you are on a budget) as the job is pretty straight forward, unplug them and remove with a simple spark plug tool or open ended wrench. Getting to them is not the easiest but it should only take about an hour tops to do it yourself in the driveway.
Thanks Jeff. So by primary you mean the ones in the front? Where are they located? I haven't searched a DIY on the primaries yet. The person who installed my DPs said theDPs would have to be removed to change them and I don't think that's true...

I did notice a more smell coming out of my exhaust, although I can't say it was fuel per se...more of an exhaust smell. Not sure if that's just my secondary cat taking a beating since I don't have primaries anymore!
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      10-19-2012, 12:02 PM   #8
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Quote:
Originally Posted by sickem View Post
Thanks Jeff. So by primary you mean the ones in the front? Where are they located? I haven't searched a DIY on the primaries yet. The person who installed my DPs said theDPs would have to be removed to change them and I don't think that's true...

I did notice a more smell coming out of my exhaust, although I can't say it was fuel per se...more of an exhaust smell. Not sure if that's just my secondary cat taking a beating since I don't have primaries anymore!
The primary o2 sensor is in front of the cat. That controls the fueling of the car, both at idle and while your driving. With that not functioning you will have fuel control problems.

Some mechanics tend to install the o2 sensor primary/secondary backwards which would cause all kinds of problems but that throws a CEL and the car does not perform well at all.

It's been a while since I did a downpipe install on this platform but with the right set of tools you may be able to get it out.

Doesn't hurt to check yourself real quick, just get the car up on jack stands and take a look. You may be able to get one from the top of the engine bay too ( again I cant recall).

There are 2 o2 sensors in each downpipe. The one closest to the engine is the primary.
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      10-19-2012, 12:14 PM   #9
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Quote:
Originally Posted by Jeff@topgearsolutions View Post
The primary o2 sensor is in front of the cat. That controls the fueling of the car, both at idle and while your driving. With that not functioning you will have fuel control problems.

Some mechanics tend to install the o2 sensor primary/secondary backwards which would cause all kinds of problems but that throws a CEL and the car does not perform well at all.

It's been a while since I did a downpipe install on this platform but with the right set of tools you may be able to get it out.

Doesn't hurt to check yourself real quick, just get the car up on jack stands and take a look. You may be able to get one from the top of the engine bay too ( again I cant recall).

There are 2 o2 sensors in each downpipe. The one closest to the engine is the primary.
Jeff, thanks. I'll try to get the car soon and take a look. Obviously my tune is on map 0 for the time being and I'm not pushing the car at all. So it sounds like I need to just replace the primary sensors like you said. I don't think they switched the O2 sensors as the DPs have been on the car since the spring and the problem/codes only just arose...

Can I ask a silly question: Is there a central front jack point on the E90 so that I can get jack stands underneath the two front jack points? Or do people just use ramps for this?
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      10-19-2012, 12:18 PM   #10
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There is a central jacking pad in the middle of the engine block. I would use ramps as it safer but if you don't make sure to place blocks behind the rear wheels so the jack doesn't slide off.
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      10-19-2012, 12:21 PM   #11
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Originally Posted by cn555ic View Post
There is a central jacking pad in the middle of the engine block. I would use ramps as it safer but if you don't make sure to place blocks behind the rear wheels so the jack doesn't slide off.
Thanks man. When I did the full brake job on an X3 I used jack stands and wheel chocks. But maybe I'll pick up some ramps...should have them anyways.
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      11-05-2012, 11:22 PM   #12
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Update...had both primary oxygen sensors replaced, cleared codes, uploaded maps again, cleared adaptations, and I'm still throwing the same codes as in the op. thoughts?
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      11-12-2012, 11:05 PM   #13
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      11-12-2012, 11:31 PM   #14
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Damn...fueling issue, maybe LPFP wearing out? How many miles on the car? How does the car idle? How is the car at start up cold?
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      11-12-2012, 11:47 PM   #15
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Damn...fueling issue, maybe LPFP wearing out? How many miles on the car? How does the car idle? How is the car at start up cold?
57k mi, new plugs and coils...car idles fine and nothing out of ordinary at startup...no codes for lpfp...codes come up even with tune taken out.
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      10-02-2013, 06:45 PM   #16
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Did you ever figure this out? I throw those same codes and have been for years with FBO and different tunes. Im dropping money in general maintenance and want to finally get ride of my CEL code, but dont want to replace all if I don't have to.
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      10-02-2013, 06:59 PM   #17
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Did you ever figure this out? I throw those same codes and have been for years with FBO and different tunes. Im dropping money in general maintenance and want to finally get ride of my CEL code, but dont want to replace all if I don't have to.
So you've never replaced O2 sensors?
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      10-03-2013, 03:59 PM   #18
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Quote:
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So you've never replaced O2 sensors?
Nope. Cars AF ratio idles at 14.6 and 11.x at WOT while hitting correct peak boost. I just want the Check Engine to be gone.
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      10-03-2013, 04:55 PM   #19
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Quote:
Originally Posted by Tommeh
Quote:
Originally Posted by sickem View Post
So you've never replaced O2 sensors?
Nope. Cars AF ratio idles at 14.6 and 11.x at WOT while hitting correct peak boost. I just want the Check Engine to be gone.
Ok well if you're throwing oxygen sensor codes then I would replace, at some point it'll start impacting driveability. Do primaries first.
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