[niksss]

Hello guys. I have a 2011 BMW E92 328i X-Drive with an N51 engine. The car has 66 000 miles on the clock. From 4-5 months ago I have strange problems with the car:
1. The fuel consumption has increased, most noticeably on highway, with 20-30%. (Before it was around 10L/100km with 130km/h and now is around 13-14L/100km with 130km/h.
2. When idling, sometimes the car is perfect and sometimes the car starts to vibrate and the rpms jump up and down (+- 100-200RPM). It happens mostly when the car is warm. Also during a cold start, the RPMs sometimes hesitate very slightly.
3. From around 1-2 months, sometimes there is a strange smell coming from the vents. It only occurs for 10-15 seconds and dissapears. The smell is of something burnt, more like plastic, but could be smell of burnt oil also, not 100% sure. The car consumes under 300ml of oil for 7-8k miles.

What could be the problem ? So far I have changed all of the coils, cleaned the vanos solenoids, cleaned the MAF, relearned valvetronic positions and Oxygen Sensor 2 before cat was replaced 6-7k miles ago. Spark plugs were replaced around 30-35k miles ago.

The codes that I get are very strange - All of the oxygen sensors throw codes. The first time that I checked all of the O2 sensors (before and after cat) were saying lean mixture. I cleaned the codes and after some time I checked and the O2 Sensors before cat were showing rich mixture and the ones after the cat were throwing lean codes. I doubt all of the O2 sensors went bad at the same time, so I don't want to throw money at them for now.

Any ideas ? A local mechanic has looked my car and told me he has no ideas what it could be. He said we can start replacing everything related to a lean/rich code, but it could get very costly.

[W37V]

There were few people who mixed up their o2 sensors during header swap. had similar issues. Which leads me to ask: Did you plug in o2 sensors back to their appropriate location? It almost sounds like your o2 sensors are off.

Did you check for oil leaks - valve cover tends to leak - or valvetronic motor gasket, and it might cause burnt smell.

[niksss]

Originally Posted by W37V

There were few people who mixed up their o2 sensors during header swap. had similar issues. Which leads me to ask: Did you plug in o2 sensors back to their appropriate location? It almost sounds like your o2 sensors are off.

Did you check for oil leaks - valve cover tends to leak - or valvetronic motor gasket, and it might cause burnt smell.

I have a small leak from the valvetronic motor gasket, but I loose very little oil.
A mechanic changed my o2 sensor, but the car ran fine for like 5k miles before this issue came along. Also I changed only one o2 sensor, I the mechanic could screw this up.

[W37V]

Originally Posted by niksss

I have a small leak from the valvetronic motor gasket, but I loose very little oil.
A mechanic changed my o2 sensor, but the car ran fine for like 5k miles before this issue came along. Also I changed only one o2 sensor, I the mechanic could screw this up.

That might be a cause of your smell.

Double check your connections.

[Savedamanualse90]

Originally Posted by W37V

There were few people who mixed up their o2 sensors during header swap. had similar issues. Which leads me to ask: Did you plug in o2 sensors back to their appropriate location? It almost sounds like your o2 sensors are off.

Did you check for oil leaks - valve cover tends to leak - or valvetronic motor gasket, and it might cause burnt smell.

Originally Posted by W37V

There were few people who mixed up their o2 sensors during header swap. had similar issues. Which leads me to ask: Did you plug in o2 sensors back to their appropriate location? It almost sounds like your o2 sensors are off.

Did you check for oil leaks - valve cover tends to leak - or valvetronic motor gasket, and it might cause burnt smell.

Does this issue throw a code?

[W37V]

Originally Posted by Savedamanualse90

Does this issue throw a code?

here is one thread after 15 sec google search : https://www.1addicts.com/forums/show....php?t=1194190

[niksss]

Removed my K&N sport filter and cleaned the MAF sensor again. Didn't fix anything. All of the errors from the previous 2 months were: 2C2B, 2C2C, 2C31, 2C6B, 2CB6 All are oxygen sensor related.
2C2B - Oxygen sensor before cat (bank 1) - system check (mixture stuck at ritch)
2C2C - Oxygen sensor before cat (bank 2) - system check (mixture stuck at ritch)
2C31 - Oxygen sensor emission control
2C6B - Oxygen sensor after cat(bank 1): system check
2CB6 - Oxygen sensor after cat(bank 1): signal fixed at lean

I have 2 possibilities for now -
1. All of the oxygen sensors have failed at the same time (highly undoubtedly I think), even that I have replaced on of the sensors soon.
2. Maybe my cat has failed ?

Anyone has any ideas ?

[matthewjmoser]

Yes I’d say the cats are definitely bad. Time for warranty work or get some aa headers.

[Moisture]

Something is killing your o2 sensors. Are you the original owner? How hard do you run the engine?

First start by checking that your fuel pressure is within spec.

If it is in spec, pull your injectors and have them inspected. Does the car smell strongly like gas after the fuel consumption became bad?



Make sure to check thoroughly for vacuum leaks. It could also be a wiring issue or something with the o2 sensors.

1. Vacuum leaks - check for failed or loose vacuum lines, leaking intake gaskets, intake air tubes loose or any other source of un-metered air leaks (leaks after the Mass Air Flow Sensor)
2. Restricted fuel filter or bent/pinched fuel system lines
3. Incorrect input from other sensors, such as the Mass Air Flow Sensor, which may not always drop a separate code

1. A leaking or faulty fuel injector
2. Fuel injector driver in computer shorted, or wiring short for injectors (likely a ground short)
3. Leaking or faulty fuel pressure regulator or restricted return line
4. Faulty evaporative emissions system - bleeding fuel vapors into engine (not commanded by computer)
5. On newer models a faulty fuel pump or fuel pump driver module
6. Faulty readings from other sensors such as a Mass Air Flow Sensor. You may actually be getting more air than the MAF tells the computer
7. Exhaust leaks before the sensor will cause erratic readings