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Author Topic: 1.8T AUQ o2 rear lambda emissions problem ?  (Read 891 times)
DwDckQo
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« on: April 25, 2025, 12:49:45 PM »

Hello guys,

First my car hw settings:
K04-023, big exhaust manifold, BAM injectors, TIP, walbro 255, N249/N112/EAGR/SAI HW deleted, Colder spark plugs 0.7mm gap
CAT on, EVAP on, suction spray pump on. My LTFT are on -2.3%... I know, I need to slightly improve my fueling maps but for now its OK.

- SAI code out by ESKONF and MSLBAS (0) MSLUB (0) [CDSLS stock, CWKONABG stock]
- N249/N112/EAGR code out by ESKONF

2 weeks ago I got rear o2 DTCs - electrical circuit breakage, lambda heating etc...

So I change my map to (rear o2 in place and connected):
ESKONF (AA FF 00 F0 FF FB FC), KFTVSAKAT (0), CDHSH (0), CDHSHE (0), CDKAT (0), CDLASH (0), CDLSH (0), CWKONABG still stock

Week ago, I was on emission control station with negative result. No DTCs + readiness ok, CO was OK - CAT working good, but my measured lambda (by technic sonde) in exhaust was at 1.10 ~ 1.20, I have higher amount of oxygen in exhaust - request to pass control is 1.03 max. My ECU req/actual Lambda was at 0.99 ~ 1.01

So, my question is:
I deleted only diagnostic of rear o2, but is it still working and slightly correcting my AFR after CAT ? I think, if its not working properly, can rear o2 sensor still giving bad values for ECU ? Should I also change AHKATMN, AHKATMX, AHKATS, AHKATSB, especially CLRSHK, CWKONABG for correct functioning without rear o2? Pre-cat o2 little malfunction ? Exhaust major leak (I have very very little leak just after silencer in the end - tested with blockage in exhaust and with started engine) ? manifold leak - (i think no.. no evidence of soot) ?

I changed downpipe gasket before control, also I pressurized only boost pipes with turbo - no leaks, but if I include vacuum/breath hoses in test i have huge leak just under cam chain tensioner (with 0.1-0.3 bar pressure)- maybe this affect AFR somehow ?

My plans are for next control: new gaskets under cam chain tensioner + valve cover, weld that little exhaust silencer leak, just for sure new pre cat o2 and make new fueling corrections by KRKTE/TVUB/FKKVS for even better STFT/LTFT ~ 0.0%. Enough ? or I have software problem ? What you think ?


THX for any answer Smiley
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Den4k29
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« Reply #1 on: May 04, 2025, 07:47:30 AM »

Hello, tell me, can you share the damos for the firmware?
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