[s-cars] UrS4 running Lean fuel mixture

Dave Tremblay da_trem at hotmail.com
Thu Feb 12 15:21:35 PST 2009

Hi all,
i'm having issues with fuel mixture with my  93' S4. About two weeks ago i've noticed on my wideband lean mixture readings while cruising and on boost.
I've always seen 14.5-15 afr(cruise) and 11.5-11.8afr on boost. Now what im seeing is 15.5-17(cruise) and 13.5-14(boost)
The car as MRC stage 2, K26#8 and a fmic for a long time now, never had a single problem with it. Motor always run on 94 oct. 
Boost pressure is the same as before and it dosent miss or anything..no leaks after the maf or after the turbo. Car is very well maintained.
Last work done recently:
New 4 bar fpr 
Relayed Fp
255 walbro fuel pump, about 2 months old
Fuel filter as 20k
New O2 sensor
New hall sender
The ecu trows no codes.
Now my question is, could a bad maf cause these problems?...
Your input on this is greatly appreciated!


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