fail smog test

Hi I know that this is not a mazda b(work truck and ongoing project) but I need some of your expertise on this.i took my '00 chevy tahoe vortec 5.7 (family suv) for a smog test and it FAIL, the guy told me that the HC(PPM) , CO%,and NO(PPM)are too high, can you please tell me what can cause this.

thank you
oth

Can you post your numbers?

How many miles are on the vehicle?

Was the check engine light on?

How many miles are on the O2 sensors?

Maybe you just need a fuel system service to clean up the injectors.

I'd put a new air filter in, clean the Mass Air Flow(MAF) Sensor and PCV valve, and check the spark plugs.

Then look here.

HC(PPM)
MAX. 100
MEAS. 124

CO(%)
MAX. 0.56
MEAS. 0.37

NO (PPM)
MAX. 975
MEAS. 670

mile on body 140k
GM create motor 3k
no engine lights
o2 was replaced 2 or 3 months before an old engine through a rod.

I'd still think the O2 sensor is bad, just because the old engine was probably sending oil fumes out the tailpipe on the way to coming apart and it wouldn't take much to poison one. The other ideas about the PCV, air filter, and plugs are also good along with cleaning the MAF sensor.

I'd have the ignition timing checked, if it's adjustable. The distributor might be off a degree or two on timing. That could have happened during installation and this is maybe the first time the vehicle has been smog checked since the work was done.

My .02. Hope you will let us know what you find out.

Well, I had my buddy come by with his code scanner and I was told that it is an o2 sensor the one behind the cat, so I replaced it and today I plug in the code scanner and the led light on the scanner is green so in a couples days iwill hit the smog again. I just hope it PASSS this time

thanks for the helps guys.

Oth

Also change the oil and PCV valve.

If you have time change the plugs and wires.

IF the nox was in range and the hc was high, it also sounds like it wasn't run hot enough either. I hope you have an oem thermostat and not a "racing" 180 or 160 therm.

By your post, it looks like the HC was the only fail.

Since the fail test I have replaced thermostat from 170 to 195, cap, spark plug wire(8.5 MSD), pcv valve, o2 sensor after cat. I will hit the smog shop again in two days.

I appreciate all of your help and info. Will update before friday
thank you , Oth