smog help

[blazinbg]

I did not pass my smog test only, wanted to know what might have caused it I passed everything except "nox" portion of the test. he said it might be the cat. but I replaced that and the egr 2 years ago during my last inspection. I am running tbi- these aare the numbers
15mph 1838
25mph 2154
want to see if there is anything I can do before i go to shop. Thanks

 

[BoondocK5]

First off what vehicle and engine are we dealing with?

Your EGR system probably isn't working correctly. A new CAT may or may not fix it.

 

[NorCal_Chris]

high nox can be caused by the following:
Misfire condition
Malfunctioning or improperly adjusted EGR valve
Failed oxygen sensor
Leak in exhaust tubing upstream of converter
Excessive carbon deposits in combustion chamber
Improper spark advance
Blocked coolant passage
Overly lean air-fuel mixture
Damaged cold air duct
Failed or malfunctioning catalytic converter
Corroded or damaged engine sensor electrical connections

 

[imiceman44]

I did not pass my smog test only, wanted to know what might have caused it I passed everything except "nox" portion of the test. he said it might be the cat. but I replaced that and the egr 2 years ago during my last inspection. I am running tbi- these aare the numbers
15mph 1838
25mph 2154
want to see if there is anything I can do before i go to shop. Thanks

If you changed the CAT 2 years ago doesn't mean it didn't go bad again, but first you better check everything that doesn't cost too much money.
You saw the list that Chris posted.
Also lots of people change the EGR but do not clean the passages which usually are the problem.
On a nissan sentra a few years back that's all we did, cleaned the passages, the EGR valve was fine.
Also if the CAT wasn't warmed up right it will not pass.
Where in CA?
As far as the timing you can be up to 3 degrees off and still be OK and to reduce the NOx they usually retard it a little more

 

[blazinbg]

should I replace it with a delco egr or an after market? any one know the part number for the delco?
1991 tbi 350