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Discussion Starter · #1 ·
My check engine light came on so I got the codes and I got a O2 sensor message, I started reading about the causes of failure and found this,

If you are not getting a voltage and the car has been running
rich lately, the sensor may be carbon fouled. It is sometimes
possible to clean a sensor in the car. Do this by unplugging
the sensor harness, warming up the engine, and creating a lean
condition at about 2000 rpm for 1 or 2 minutes. Create a big
enough vacuum leak so that the engine begins to slow down.
The extra heat will clean it off if possible. If not, it
was dead anyway, no loss. In either case, fix the cause of the
rich mixture and retest. If you don't, the new sensor will
fail.

if I just change the sensor with out doing this procedure will the new sensor fail?

any help on this appreciated.
 

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It may not be running rich. it may just be a bad O2 sensor. they wear out with time. If the outside of the sensor has become covered in oil or petrol, if someone has used Exhaust Joining paste between the manifold and the sensor, if someone has used silicon sealer ANYWHERE in the engine bay, or if you have used some poor quality fuel. This will all ruin the O2 sensor. They are fragile, and if the sensor has broken for any reason this can cause the engine to run lean/rich on its own as it helps control the fueling.

I would just get a New sensor put in and if you are worried about over fueling, then get the exhaust gas checked at a test station/dealer/specialist.

P.S. making the engine run lean could damage the engine. I would not advise it.
 

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Discussion Starter · #4 ·
thanks for the info.
I know its running rich, because it guzzels gas. Will this damage the engine?
My knock sensor came on too, but I think that it may be because of my bolts falling off the water pump that created a repetitive knocking for about 20ks until I realized it. Now that the knock sensor is part of the check engine light will it go away with a battery reset or do I have to change the sensor too?
 

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If there is too much fuel getting into the engine, the extra fuel gets turned into soot. That can fowl the plugs, maybe block your cat and O2 sensor. but the only Bad engine damage, is if there is enough fuel getting into the cylinder to condense on the bore wall and get past the piston rings. This is called bore wash, and can increase bore wear, and will dilute your engine oil and cause wear in the crank and cam bearings. But that will only normally happen if you have an injector stuck open all the time. I doubt that is happening so don't worry.

I'm not sure what you mean about the knock sensor? I don't think it would pick up a mechanical knocking sounds.
It is there to detect pinking (pre-ingition) caused by the spark happening too soon. the engine is more powerful with more advanced ignition, but if you use low octane fuel (as most of the US does) the spark needs to be retarded to avoid pinking.
The DME tries to advance the ignition till the knock sensor detects pinking, then it retards to just prior to the pinking. But the knock sensor is always active, and basically just lets the engine adapt to different fuels.

If the check engine light is on, the engine knows that something is wrong, but wont know what, so it ignores some of the sensors, and will give its self the best chance of running in any condition. That is "safe mode" or "get you home mode" That means it will over fuel, retard ignition way back and stuff. It will be less powerful and use more fuel but should get you home.

If something is wrong and the check engine light come on. it will normally stay on till the engine is turned off. If the light is always on then something is still wrong. it will work out cheaper to get someone to check the fault codes.

Most garages can check and reset the light, but it will only give a hint of whats wrong. BMW or an independent BMW specialist will have a more accurate system that will tell them exactly what is wrong.
 

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The Biggest P0st Whore!!
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With the e34 you can get just as much info on the engine as a shop or the dealer using the stomp test. The only things they can get that you cant are SRS, ABS, and trans fault codes (you can get them too if you have the right code reader).
 

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I'm sorry. I'd forgotten about the stomp test, I tried it a while back and it didn't seem to work. But I have a friend with a shop who lets me use his code reader so I gave up on it.
I bet the stomp test gives more info than some code readers, as it is all BMW specific, and not just universal.

But again I'm sorry.
 

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Discussion Starter · #8 ·
I tried the stomp test many times, even my shop guy tried it. They didnt have the adapter for reading bmw engine codes. I found one that does and got the O2 sensor and knock sensor codes he isnt a bmw specialist or anyting though. Im going to change the O2 sensor on friday, should I reset the battery first? Im sure the previous owner was running the car on cheap gas. Since I have had it I been using the good stuff. The first owner was a dentist, he owned it for 10yrs before trading it in. The second owner had it since 2003 until 2007 so im the third one. Im just hoping I can keep her for another 10!
She seems to be high maintnance..hehe

thanks alot for your input about the O2 sensor
 
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