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BMW E92 02 sensor possible problem.

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21 Jan 2019 09:17 #26374 by steve86
BMW E92 02 sensor possible problem. was created by steve86
Hi Paul and everyone. I'm Steve from the UK.

Paul I would just like to say a massive thank you for all the information and videos you put up for us all on a daily basis. If it weren't for your expertise I certainly wouldn't have a idea about cars.

I have a BMW e92 N43 engine and I had the exhaust welded as I had a severe leak. This was located between the upstream and downstream o2's. I have no errors on the car at present but know the car is not running correctly. My Ltft's are at 9% idle. Decrease with higher RPM to hear enough perfect. I selected all o2's on scan tool and my upstream both seem to stay at 1.999 max rich and the downstreams are 0.000v. If I blip the upstream they do move but stay at the high end and the downstreams sit around 700. As soon as I release the RPM they max out again.

Am I thinking correct, that my upstream's are dead and that's why my downstreams and ltft are where they are?

Thank you, would be very grateful for some information.

Kind regards
Steve.

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21 Jan 2019 09:58 #26377 by Tyler
Replied by Tyler on topic BMW E92 02 sensor possible problem.
Hey steve86, welcome!

Based on what I know about BMW air/fuel sensors, I'm guessing you're looking at a severe lean condition at idle. 1.999 would actually indicate a lean condition, and the downstream sensors reading 0V would confirm that. Getting a reaction from the sensors off idle would suggest a vacuum leak. That would also suggest to me that the sensors are working and (probably) telling the truth.

Would it be possible for you to post screenshots of your scan data at idle and 2500?

As far as vacuum leaks, I don't believe we got the N43 in the US, so I have no experience with it. :( Visual inspection on the intake and PCV tubing would be a good start. Also check for excessive vacuum in the crankcase.
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21 Jan 2019 10:22 #26381 by steve86
Replied by steve86 on topic BMW E92 02 sensor possible problem.
Thank you Tyler for your quick reply. I had it in my head that the 1.999 was rich for some reason. I will certainly post up some screenshots. If the exhaust repair was not sealed correctly could this effect the upstream sensors running lean also?

Kind regards
Steve

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21 Jan 2019 10:39 #26383 by Tyler
Replied by Tyler on topic BMW E92 02 sensor possible problem.

steve86 wrote: If the exhaust repair was not sealed correctly could this effect the upstream sensors running lean also?


Eh, it's possible? But they'd have had to do a fairly horrible job of fixing it. :lol: In my experience, exhaust leaks need to be HUGE and within inches of the sensor to have a significant impact. Honestly, if the car doesn't sound like a two stroke at idle, I wouldn't worry about it at this point. ;)

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21 Jan 2019 12:21 #26391 by steve86
Replied by steve86 on topic BMW E92 02 sensor possible problem.
Here's some attached pics of idle and 2500 rpm. Thanks.
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21 Jan 2019 12:26 #26392 by steve86
Replied by steve86 on topic BMW E92 02 sensor possible problem.
Some more attachments.
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21 Jan 2019 12:29 #26393 by steve86
Replied by steve86 on topic BMW E92 02 sensor possible problem.
Some more. Thanks.

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21 Jan 2019 12:39 #26394 by Paul6004
Replied by Paul6004 on topic BMW E92 02 sensor possible problem.
I'm just wondering if the oxygen sensors were removed to do the welding and whether welding could damage them or not?

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21 Jan 2019 12:44 #26395 by Tyler
Replied by Tyler on topic BMW E92 02 sensor possible problem.
Thanks for the shots! :cheer:

Some of the captures show an improvement off idle? But then some don't. :silly: I see what you mean about the upstream air/fuel sensors at idle, too. They're showing very lean. Can you confirm that the LOOP PID shows Closed at idle?

I also see the MAF g/s reading at idle is low, which may suggest a pirate air or vacuum leak issue.

It would also seem that there's an issue with the B2S2 O2 sensor, as it shows over 1V at all times. I don't believe this is related to your issue, but may be worth investigating after we clear up the lean condition.

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21 Jan 2019 12:46 #26396 by steve86
Replied by steve86 on topic BMW E92 02 sensor possible problem.
Hi Paul,

The condition was the same with the car before the exhaust was repaired with the leak.

This is really throwing me, the percentage seems to be rising to.

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21 Jan 2019 13:01 #26397 by Paul6004
Replied by Paul6004 on topic BMW E92 02 sensor possible problem.

Tyler wrote: It would also seem that there's an issue with the B2S2 O2 sensor, as it shows over 1V at all times. I don't believe this is related to your issue, but may be worth investigating after we clear up the lean condition.

Question: If some vehicles also use sensor 2 to adjust fuel trims could a fault with sensor 2 reading wrong cause the ecu to over-ride sensor 1 trims causing them to show lean - since the ECU is doing what it needs to get sensor 2 reading right?

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21 Jan 2019 13:08 #26398 by steve86
Replied by steve86 on topic BMW E92 02 sensor possible problem.
Thanks Tyler.

That B2S2 O2 does drop eventually to react the same as the other but takes time to do so.

The car does seem lumpy. I can confirm they are in closed loop.

It seems to be getting worse as it was 9%. Now getting to 14 and 15%.

With the Air/Fuel sensors do they react opposite to those of normal o2's?

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21 Jan 2019 13:10 #26400 by steve86
Replied by steve86 on topic BMW E92 02 sensor possible problem.
Paul, that was exacting what I wanted to find out to. Could it be that the 02's are throwing the others out in turn messing the fuel trims.

Cheers guys for your replies I'm very grateful. : )

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21 Jan 2019 13:32 #26402 by Tyler
Replied by Tyler on topic BMW E92 02 sensor possible problem.

Paul6004 wrote:

Tyler wrote: It would also seem that there's an issue with the B2S2 O2 sensor, as it shows over 1V at all times. I don't believe this is related to your issue, but may be worth investigating after we clear up the lean condition.

Question: If some vehicles also use sensor 2 to adjust fuel trims could a fault with sensor 2 reading wrong cause the ecu to over-ride sensor 1 trims causing them to show lean - since the ECU is doing what it needs to get sensor 2 reading right?


Sure! Downstream fuel control is totally a thing some makes/models do. But, in this case, I don't think that's what's going on. In the first set of pictures, both banks are trimmed around 14% positive. B1S2 is showing lean, but B2S2 is beyond full rich. If the ECU was chasing the downstream sensors, I figure the bank one trims would be maxed positive, and the downstream would be maxed negative.

I dunno about BMW, specifically, but I usually find that downstream fuel control systems don't start working until the engine is off idle and the car is cruising down the road. Just my experience. :)

That B2S2 O2 does drop eventually to react the same as the other but takes time to do so.


Then it may be that the B2S2 heater is weak, or the PCM doesn't run it's heater until other conditions are met. Either way, I don't believe the downstream sensors are skewing the others. If you wanted to make sure, you could unplug both downstream sensors and recheck the trims.

With the Air/Fuel sensors do they react opposite to those of normal o2's?


Yep! In your case, I'm reasonably sure that positive current represents a lean condition, and negative represents a rich condition. You can confirm this by adding fuel to the intake (propane, carb clean, whatever) and watch the upstream sensors. Both should go negative.

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21 Jan 2019 14:07 #26405 by steve86
Replied by steve86 on topic BMW E92 02 sensor possible problem.
Hi Tyler,

Thanks for your feedback. So it would be worth putting propane into intake and see results. Where would be best to put it in?

If it riches up, o2s confirmed fine and as you stated vacuum needs to be found. I'll have to give the water test a go. I'll also unplug the downstreams. Am I write in saying that they should both be 4.50v once unplugged Or is that manufacturer specific?

I have only just started studying the motor trade as I have a massive interest in it. So grateful to Paul Danner and you all for all the info at hand. I have so much more reading and watching to do. Cheers guys!!!

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21 Jan 2019 14:56 #26408 by Tyler
Replied by Tyler on topic BMW E92 02 sensor possible problem.

steve86 wrote: Thanks for your feedback. So it would be worth putting propane into intake and see results. Where would be best to put it in?


Somewhere behind the MAF, preferably. TBH, since I've never had eyes on your engine, it's tough to recommend a specific location. :blush: Assuming there's a rubber tube between the MAF and the throttle body, you could loosen the clamp and get the tube off enough to spray some cleaner in.

The brake booster hose is another option? But the last time I tried this on a BMW, I couldn't get the fitting out of the booster. :silly: German plastics are a liability, so try not to disturb them if you don't have to.

While you're there, try checking for crankcase vacuum with the engine running. Pull the oil fill cap off and cover the opening with your hand. If it tries to suck your hand in, there's a problem. If you feel some gentle suction, don't worry about it for now.

I'll also unplug the downstreams. Am I write in saying that they should both be 4.50v once unplugged Or is that manufacturer specific?


It's definitely manufacturer specific, and I have no idea what BMW uses for a bias voltage. Or if they use one at all. :lol: If you wouldn't mind, could you take a shot of the scan data with the sensors unplugged? So we have a known good open circuit reading.

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21 Jan 2019 15:29 #26411 by steve86
Replied by steve86 on topic BMW E92 02 sensor possible problem.
Thanks Tyler I'll do all that and will post up my findings.

If there is a lot of pressure there what is usually the problem?

I did notice that my IAT temperature was near 30 Celsius which was a lot higher than my usual reading. Our temp at the moment is around 5 Celsius.

Kind regards
Steve.
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