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Discussion Starter #1 (Edited)
Hello,
i have a problem with my M5 E39 2000* that now have 100200 Kms (* the car is end July 1999 and it's a 2000 model).
I must say that i live in France and the car is Italian origin because probably the US M5 E39 have some difference with it and i buy this car 2 years ago and it's a fabulous car (my M5 is Italian origin but don't know the difference with French or US version,... just that exaust system under the car seem look different but to be sure need to see picture of same year US car i think)

Yesterday, it was time and date for making the control of the car in a control center and i'm late.
I see that i'm low fuel (to make aprox 50 kilometers) when i start but i have no time to stop to the fuel station because i'm late for the control and center is very close from my home.
I have a strange sensation in the car and on the steering wheels like tires flat or engine problem or shock absorbers...
I drive slowly (but take care that engine temperature was not too cold for the test) and when i arrive to the center garage for the control i speak to him about the problem and he first make a control of the 4 tires pressure (missing a lot of pressure on all tires).
I have not used the car during one month and probably it's the origin of this problem because one month later air temperature was very more hot.

And after he begin to test the car for CO (CO is OK) and also for O2 value (named here lambda).
For the M5 E39, the value for O2 must be >0.97 and <1.03 between 2500 and 3000 RPM
The big problem, my M5 E39 just started on the idle is already more than 1.03 ! (1.039 to 1.04X because he test with and without clim to see)
At 2500 RPM value of O2 is very more high (don't remember sorry)
He say that it's not possible to accept the car with this problem of O2.


But this person never test CO and O2 on a M5 (and more generally on a big engine car) and have a doubt.
He don't know if he must control only one exhaust or two exhaust at same time or the four at the same times (the system is a sensor that he just put on the exhaust and launch computer that test value of CO,O2...).
He simply control one exhaust at a time and try the others one by one but same value > 1.03
Because he is not sure how to control O2 on this car, he prefer ask tomorrow to an other person and decide to not save the car in her computer to be defective and ask no money for the control.
It's like i never pass the car to the control center just that i know now that i have certainly a problem (and i have to make this control again later with no problem on O2).

I test the car after on a small road (not very good road), and with the new tires pressure (think 2.4 front and 2.6 rear) the car is better but i have a strange sensation in the steering wheels.
I will have to test on a better road to confirm.
Else car seem run ok and fast and i have no problem of engine power (i try slow/middle/full power on 2-3 or 3-4 or 3-4-5 a lot of time to see)
I not see (i must take more care about) light or error code that give me indication of a problem.

My question is what do you think is the problem of O2 value ? (MAFs that i think never changed on my car ? O2 sensors also i think never changed ? low fuel in tank ? not use of the car during on month ?, that i drive slowly to go to the control,... ?)
Probably because the car have more than 100000 kms it will be a good thing to change MAFS sensor and also the 4 O2 sensors, what do you think ? (i just hope if i change MAFS and the 4 02 sensors i will not have problem with O2 value on next control ! else ouich )
 

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fumaras said:
Hello,
Probably because the car have more than 100000 kms it will be a good thing to change MAFS sensor and also the 4 O2 sensors, what do you think ? (i just hope if i change MAFS and the 4 02 sensors i will not have problem with O2 value on next control ! else ouich )
High lambda values can indicate contaminated MAFs.

How to test the MAFs yourself and How MAFs work
http://www.m5board.com/vbulletin/showthread.php?t=54788

MAFs and O2 sensors rarely last more than 75000 kms.

Sometimes it helps a lot to get the catalysts really hot befor testing. Scedule a re-test, but this time drive the car the last km in 1st gear at high revs. This will make the cats very hot.

David
 

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Discussion Starter #3
hello,
think my first post is too long probably.

Simply for my M5 E39 2000 :
If O2 value normally at 1.00 is too high (>1.03) what i must begin to look ? (MAFs ? change O2 sensors ? ... ?) and important, i have no error light or code and i haven't problem with engine power.
 

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Discussion Starter #4
Thank's DavidS i just post at the same time and not see your answer.
I will start with the MAfs like you say and try to arrive at the control with catalysts really hot.
 

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Discussion Starter #5 (Edited)
Just add that this problem of O2 value too high (>1.03) was indeed solved by cleaning the 2 MAFs sensors.
Now O2 value test is ok (= 1)
Thank's again Davids :cheers:
 

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That is great!

The lambda value is measured at idle and increaed idle. At full load the engine uses a lot more air. The ok lambda value at idle tells you the MAFs now work at low airflows.

I´d suggest to perform the fuel-flow MAF test as per earlier post in this thread. That will tell you how well the MAFs work at full load. Maybe there are some HP to be gained...

David
 
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