Crap, I failed smog! Please provide your insight

[m3f_mbobkat_3cf0f2f02a]

Hi all, welp it finally happened - I failed smog today. I've got a 97 with 141k on it. I've used this smog station every time and they do a great job...they we're feelin my frustration today when it failed. Here are the results:



HC (PPM)

MAX=54

AVG=9

I measured=3

PASSED



CO (%)

MAX=0.50

AVG=.02

I measured=.01

PASSED



NO (PPM)

MAX=430

AVG=57

I measured=641

FAILED



By Cali law the smog stations can't diagnose for you. After I told him some recent history (my check engine light has come on and off the past couple of months and I have never replaced any of the four o2 sensors), he agreed that it is likely to be an o2 sensor.



What do you all think? Is it likely to be the oxygen sensor(s) or something else? This is where my mechanical inclination kinda come to an end.



Any help here is greatly appreciated. I think since I haven't replaced them yet, I'll go ahead and dish out the 400 bucks for them.



Will replacing the plugs and wires help much? I know to run it hot before having it tested and did so.



I friggin hope its not the CAT.



Thanks in advance your your feedback.



Late,

~B

[m3f_Z Driver_38bb5042f3]

It could be the O2 sensors. Did you do the test after the car had a chance to fully warm up? Cars run dirtier when cold.

[m3f_SG_M3_d1201712b5]

Probably an o2.



The car needs to be HOT, very not. E36's have a hard time passing unless they are hot, hight rpm's for a while before you take it it. Make sure it doesn't sit, it should be hot when they test it.

[m3f_mbobkat_3cf0f2f02a]

Great, thanks for your help fellas

[m3f_salty_80d4b8491b]

I always drive to my smog test one gear too low. Clean oil will often make a difference for the HC...which you passed anyway.