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Discussion Starter #1
Has my car on the rollers on Sunday, but it only made 287bhp, mostly due to fuelling by the look of it.
The AFR was over 15:1 at WOT when it should have been around 13:1 so the car is ultra lean.
The guy ran a code reader and it showed the pre-cat probes reading was up and down with vastly dissimilar readings constantly.
Anyone else had a similar problem or know what the o2 probe readings should be?

The post cat probes were nice and stable.
 

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points towards inlet and mixture to me any vacuum leaks or an iffy MAF would upset the ECU which would be constantly altering the fuel air mixture in confusion..

M3 has individual throttle bodys so any above issues on the bodys not so much the MAF.. it would tend to pertain to one bank of 3 pre cat sensor instead of both depending on which (if there is a suspected leak) throttle body on which cylinder in the banks of 3..

all guesswork like i don't own an M3 just from an engineering sort of background..

double check all throttle body short hoses condition and clips i would first..
 

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Discussion Starter #3
Nice one, i'll do that.
thought it was a bit odd that both o2 sensors would both be faulty to exactly the same spec
 

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always perplexed me why BMW have never fitted the old valvetronic technology to any M series engine if its supposed to be so good and improve power delivery and efficiency..



im a cynical sod i think they know its sh+te long term and prolly not a good advert for the talisman of the BMW range..
 

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Discussion Starter #5
Can't find any split vacuum lines, in fact there are not hardly any anyway..

Not sure now whether to replace the MAF or the o2 sensors
 
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