high NOx reading Cali smog

[2001goldGTP]

Does anyone have experience with this? My car failed for the first time ever. I have heard I may need to decarbonize the motor aka seafoam. Help with ideas on how to lower the NOx emissions? Thanks

[Nas Escobar]

Isn't NOx the one that basically means the cat isn't doing its job? Might also look at the EGR.

[RobertISaar]

do you have numbers available? especially past test results? being able to compare all 3 tested gasses(it is still 3, right?) is helpful.

[55trucker]

Is the original cat still under the car?........if so I'd start there and replace it with a new three way cat, can't speak for Cali but here in Ontario our emission regs closely match that of Cali & the original cats of these period cars *OBDI* will not pass the standards here allowing high NOx readings.

[Schurkey]

EGR is the primary "cleaning" solution for high NOx. Start with the EGR system, including tracing all the exhaust passages as they tend to plug with carbon, as do the valves in the solenoid assembly--at least on the older cars, those were the typical problem areas.

 

A three-way cat can deal with the remaining NOx--but there shouldn't be much for the cat to do, and your vehicle may or may not have provisions for the 3-way cat.

[2001goldGTP]

So this has been my hell...

I put a smoke machine on it, huge vac leak at both egr gaskets. Replace, my NOx stays high then my hydrocarbons go sky high, Wtf right?.

I notice my O2 wire is on the exhaust manifold and crusty, so I get a new acdelco one. My buddy's scan tool still says the car is lean, Wtf. The fuel pressure reg I changed about 20 months ago has failed and is leaking fuel. Changed that with a new acdelco one. Went to smog again, everything is fine but I missed on HC by 3 ppm. 3!?!. The cat was a cheap one put on in 2005 before Cali got nuts with cataylic converter laws. So my O2 and CO2 are high but the scanner says its good. So I was able to find a CA legal cat on amazon for $130 over nighted to my door. Then I have to get it welded on and go again. It literally has not been this healthy in years. 165k mile service plan?

[Schurkey]

huge vac leak at both egr gaskets. Replace, my NOx stays high then my hydrocarbons go sky high, Wtf right?.

WTF indeed. Did you check for plugged passages? NOx high is a sign of lack of EGR, although abnormally high combustion temp could be from a hot engine and/or lean fuel mixture. High hydrocarbons is a sign of misfire.

 

 

I notice my O2 wire is on the exhaust manifold and crusty, so I get a new acdelco one. My buddy's scan tool still says the car is lean, Wtf.

So IS the engine lean? You'll have a false "lean" indication if any of the cylinders are misfiring, by the way.

 

The fuel pressure reg I changed about 20 months ago has failed and is leaking fuel. Changed that with a new acdelco one. Went to smog again, everything is fine but I missed on HC by 3 ppm. 3!?!.

High HC is also a sign of cylinder misfire. It is NOT a sign of rich mixture unless the mixture is WILDLY rich.

 

The cat was a cheap one put on in 2005 before Cali got nuts with cataylic converter laws. So my O2 and CO2 are high

High O2 can be lean mixture or misfire. High CO2 is a sign of rich mixture. Having the two together seems to be a sign of rich mixture and misfire. [LATER EDIT!!!!! My mistake--High CO (not CO2) is a sign of rich mixture.]

 

 

but the scanner says its good.

What scanner gives you data about CO2?

 

So I was able to find a CA legal cat on amazon for $130 over nighted to my door. Then I have to get it welded on and go again. It literally has not been this healthy in years. 165k mile service plan?

First Guess: You still have unresolved issues with the engine that result in high emissions. The new cat may "fix" this for a little while, but the engine problems will eventually cause cat failure...again.

 

Second Guess: Find out why the engine is misfiring. High O2, high HC are both signs of misfire.

Edited January 1, 2015 by Schurkey

[2001goldGTP]

sorry i should have wrote that a little better, i was tired,

 

The egr gaskets where almost gone, like non existent, the egr and passages are good. The car was very lean because it was only getting 32 psi of fuel through the regulator. The minimum pressure to run according to the factory manual is 32 psi. Now it has about 45 psi. the CO2 and O2 numbers come from the smog sheet, i will post when i get home. The car is not lean according to the fuel trim levels seen by the scanner. the car is great now

[2001goldGTP]

also the new numbers are great just the HC on one of the two tests failed, also I do not hear any misfires

Edited December 30, 2014 by 2001goldGTP

[Nas Escobar]

Misfires sometimes are not heard, but are felt. Not all misfires are classic stumbling complete with popping sounds and other sounds. Sometimes a misfire is a shake, or a surge. Does your RPM fluctuate at all? Do you feel any vibrations that wouldn't be labeled as normal?

[2001goldGTP]

 

The car runs great, smooth idle at around 580 to 620 depending on HVAC loads. The top report was the first and the bottom was the third test. I don't have the print out for the second test. The second test the only thing different from the first is that the HC went to 205. The cat got here today, someone quoted me $90 to put it on but can't do it today or tomorrow

[Schurkey]

Maybe the fresh cat will clean this up. You are not far away from passing as-is.

 

I look at 0.00 CO and think the engine is still a hair too lean.

[2001goldGTP]

Watching the fuel trim numbers on the scanner and its about as dead on as you can get. I bought the gm j tool to test the injectors and see if one isn't as strong as the rest. I need the car to pass already I have been borrowing a friends car since August when the transmission broke

[2001goldGTP]

it finally passed, the cat dropped everything to about 0 except the NOx, no idea but i will be keeping an eye on it and may even run some GM top engine clean through it