I had posted this on the original thread from 2 years ago. I hope it's OK if I open a new thread.
Here I am again. The car barely passed last time so considering that I had over 300,000 miles on the engine I replaced it with a low mileage used engine. The car failed again this year.
Latest test:
Co2. O2. Hc. Co. Nox

15mph 14.5. .3. 45. .04. 646
25mph 14.5. .2. 38. .04. 626

Car runs great, gas mileage is good. Lambda is 1.012- normal. Idles good. Smoke tested for vacuum leaks. No vacuum leaks. All vacuum hoses new. O2 sensors new. No exhaust leaks. Fuel trim is normal. Fuel pressure normal. New Delco pump & regulator. EGR valve & solenoid new. Optispark new. Cat is new. Replaced again with higher load cat. Tried forcing EGR valve open, no help with NOX. EGR flow is good. EGR system tested OK. I have the car at a Star smog station and they are running out of ideas. I am going to replace the injectors next. I also guess I need to do a carbon clean out. Does anyone have any other suggestions? The smog guy said the NOX goes down if he forces the car a bit richer I have had this car for 10 years and never even had an issue with smog! Please help.
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I thought you had virtually the same problem two years ago. Now we've lost the tie back to what happened last time, and how you solved it.

https://www.camaroz28.com/forums/lt1...ck-nox-826934/

 

Sorry about that. I actually posted on the old thread originally but I guess I got impatient This problem has me tied up in knots. It finally passed 2 years ago by a hair after top end cleaning multiple times. I have since replaced the engine thinking it was due to the extremely high mileage (300,000+). I was a smog tech for 20 years & the shop I took it to came very highly recommended. We just cant figure it out. Any help would be greatly appreciated.

 

Depends what cat you bought. The Walker or Brown ones are more like OEM with good quality Palladium, Rhodium, and Platinum cores. Many of the aftermarket ones skimp on those metals, because they are expensive, and they won't scrub the emissions near as well. I had a high flow Random converter, about a year old and my car failed a couple times. I replaced it with the original one that had maybe 17k miles on it and it passed with 10x better HC, 5x better CO and 2x better Nox with no other changes. Other than that, maybe a gallon of alcohol in the tank would help a bit.

 

Thank you for the reply. The catalyst is a Magnaflow cat. The first & second ones were a bit skimpy. I spoke to Magnaflow & they suggested a higher load cat. I would love to get hold of a new or low mileage original catalyst if anyone has one for sale? The smog shop recommended an OE cat but they are not available. I never had smog problems till the catalyst failed due to a misfire.

 

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Anyone?

 

You might check Rock Auto for the cat.

 

Thanks. Tried everywhere for genuine GM catalyst. I'm hoping Someone here may have one they took off their car.

 

Anyone?

 

it might be worth researching a reputable lt1 tuner in california(any that have hard smog testing) as well as a couple of the email tuners as they may have a couple tricks( like changeing pulsewidth or setting the afr different). I dont have any smog requirements were I live so I know next to nothing but I have a problem solvers mentality. I do know some people load smog tunes and thats the direction I would steer along with what aftermarket cat may work(given you cant find oe). Another thought is could you run dual cats rather than a single. Again I am ignorant about smog testing but throwing out ideas that may spark a solution. Good luck and report back any progress.


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I told you exactly what to do and I found a direct fit 49 state legal EPA converter for your car in less than 2 minutes for $369 with the Y pipe.

 

Thank you all for the help and advice. I learned from the good people at Magnaflow that any aftermarket cat is only 50-60% as effective as an OEM cat. My experience has shown that to be even lower for nox. Due to high compression our cars produce a bit more nox then most. I also learned after spending $$$$ that my car has nothing wrong with it. I'm still looking for an oe cat. Thanks again for all the help.