92 SL2 DOHC failed smog test - 15mph NOx

[Bill Mudd]

92 SL2 - DOHC

The only part of the California smog test it
failed was the 15mph NOx.

My reading was 901ppm with 835ppm max allowed.
The 25mph NOx was half the max allowed.

The HC was 80ppm with 130ppm max and
the CO was .06% with .80% max allowed.

What are some of the things that might be causing
a high NOx with everything else OK?

I don't know much about this stuff.

Thanks,

Bill Mudd

 

[Philip Nasadowski]

92 SL2 - DOHC

The only part of the California smog test it
failed was the 15mph NOx.

My reading was 901ppm with 835ppm max allowed.
The 25mph NOx was half the max allowed.

The HC was 80ppm with 130ppm max and
the CO was .06% with .80% max allowed.

What are some of the things that might be causing
a high NOx with everything else OK?

I don't know much about this stuff.

Check the EGR valve for proper action. IIRC, it controls NOx.

 

[James1549]

Check the EGR valve for proper action. IIRC, it controls NOx.

That is my first thought also, but that should trigger the SES light.

Also I am not sure the EGR valve operates at 15 mph.

James

 

[Mike]

Probably not, but a leaking EGR (stuck partially open) might cause enough of
a problem to fail the test, and not trigger the SES. Been there, done that!