Need help on smog in California

[trail_runner]

I barely didn't pass smog!!!! NOX failure
No check engine light on either.
Is there a way to detect what exactly need to be done.
295k. It did recently have a blow headgasket but now good. Wonder if I just got antifreeze in exhaust?
Smog guy told me maybe try seafoam.???
Any suggestions?

 

[Royisme]

Seafoam is cheap enough that I'd try that out first, and then be stoked if that's all it took!

 

[Mike&Ike]

Is your cat oe?

 

[trail_runner]

Magnaflow exhaust, but two yrs ago I went to this same guy and it passed fine.

 

[J. B.]

Did you go straight in to smog........so cat wasn't hot enough?
Try driving around with a heavy right foot before you get tested.

 

[snow junky]

if you have 4cyl check your egr...... you need to make sure your cat and engine are heated up really good. nox is caused by high combustion temp (air going into cylinder is cold)

 

[t4r4life]

high nox is usually means the truck is running to lean/hot, most of the time is dirty EGR or a bad CAT, Do not try seafoam it won't help you in this case. if i were you i get a bottle of this

and then go to the gas station that has the worse gas. bad gas=better for smog, drive the truck on the freeway in 3rd gear for a while then go smog it.

 

[Stick Figure]

Basically anything that can cause you to run lean can contribute to this problem.

How is your fuel system? are your fuel injectors original and never been cleaned? how about o2 sensors? If you have access to a scan tool how do your fuel trims look?

Other question would be how did the combustion chamber look when you had it apart for the head gasket? if you had lots of carbon build up this can cause this issue as well.

 

[hugo2go]

I had the same situation in July when I did my smog. I'm at 189K, and my rig barely passed. Luckly my 02 sensor finally gave out after the smog check.
So I would say run the seafoam with Chevron 91 octane. If that doesnt work, then swap the O2 sensor for a new one.

 

[stevec5000]

I barely didn't pass smog!!!! NOX failure
No check engine light on either.
Is there a way to detect what exactly need to be done.
295k. It did recently have a blow headgasket but now good. Wonder if I just got antifreeze in exhaust?
Smog guy told me maybe try seafoam.???
Any suggestions?

Nox failure means the Exhaust Gas Recirculation isn't working. I have a lot of experience with that here in AZ since I have to take my pickup on every 2 yrs for emissions. If CO fails that means it's too rich, Unburned Hydrocarbons means it's missing due to ignition problems and NOX means problems with EGR. Might just be a split or loose rubber hose. You have to use an expensive exhaust gas analyzer to check it but if the EGR is working at all it should be OK. You can tell if it works by applying a vacuum to the EGR valve at idle and it will kill the engine.