Failed smog badly, any suggestions?

[jayuuey]

I attempted to get CA BAR certified today but failed smog terribly. Any suggestions on where to start?

S50 out of a 95 m3, 04/1994 production date, 172k. Head appeared to have been redone at some point.
506 dme, stock tune
Typical reseal minus head gasket
New knock sensors
80 deg thermostat
Cone filter on MAF (passed visual since obd1), new intake boot
Oem mid section (low miles according to seller)
O2 sensor likely original to midpipe/cat
E36 rear section

Runs good, idles fine.

Thanks.



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[2mAn]

Id start by replacing the o2 sensor, especially if its the original! The NOx is BAD though

[Daeldalus]

The colder thermostat likely has something to do with it too. The stock tune is set for a hotter thermostat. A colder one would cause that tune to run a bit rich.

[DesertBMW]

80 deg thermostat
Cone filter on MAF (passed visual since obd1),

80f is low for thermostat in my book, that will make the CO and HC higher than normal. Cone filter directly on MAF will mess up the reading, got to have some piping after the filter to smooth out the flow of the air. NOX is high also. When all 3 fail is good indication catalytic converters are bad.