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  #1  
Old August 31st, 2020, 08:43
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blu3fan blu3fan is offline
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High NOX every year

Hey guys.
For the last few smog tests I keep scoring 700 on nox and need 400 to pass.

Last year.
I replaced the plugs. Re-adjusted my distributor back a few degrees and I passed.


This year.
Just got back
Same score as last year.

2nd attempt I will do the same thing. Replace spark plugs and retard the distributor 2-3 degrees. (Yes I know adjusting the distributor is not supposed to effect this. but every year I do this... and It has worked so far.)
Im also going to try octane booster since my strokers compression ratios are a little higher.


any other tips aside from make sure the cat is HOT?
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  #2  
Old August 31st, 2020, 10:20
Black1990jeep Black1990jeep is offline
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Re: High NOX every year

A new cat can do wonders to clean up NOx. A california type cat even more so. I always recommend a new O2 sensor when replacing the cat, as a weak or slow O2 sensor (one that cycles slowly) can poison a new cat pretty quick.

you might want to consider a california type cat for test purposes only, retaining your old cat, or a test pipe for other use where legal to do so of course.
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  #3  
Old August 31st, 2020, 11:02
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Re: High NOX every year

I replaced the cat in 2012 with a hi flow Magnaflow 91005 Universal 49-State Catalytic Converter 2.25'' -

Not quite sure it's the cat.
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  #4  
Old August 31st, 2020, 11:03
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blu3fan blu3fan is offline
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Re: High NOX every year

O2 sensor is 6months~. old one was 2 years and I still have both.
I suspect no issues with new O2 sensor
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  #5  
Old August 31st, 2020, 11:28
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Re: High NOX every year

Get an IR thermometer and check the inlet and outlet temps of the cat. Drive around and get the cat hot first. You should see a much hotter temp at the outlet.

A CARB certified CAT will cost triple a 49 state.
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  #6  
Old August 31st, 2020, 18:24
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Re: High NOX every year

honestly my cat is welded into my current setup.

I do not have an IR thermometer. might be a good addition to the toolset.

I will consider replacing/getting a "smog exhaust"
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  #7  
Old August 31st, 2020, 18:26
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Re: High NOX every year

Any suggestions on which cat to buy?
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  #8  
Old August 31st, 2020, 18:29
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Re: High NOX every year

***Opens Ebay... see's banks monster exhaust....
maybe I should replace this ebay pipe while im at it.
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  #9  
Old August 31st, 2020, 18:42
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Re: High NOX every year

May 9, 2013 was when I got this cat. with 10 years being the shelf life I might just replace it.
Good call
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  #10  
Old August 31st, 2020, 19:06
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Re: High NOX every year

Items purchased.

Flowmaster 942447
Magnaflow 91005
Spark plugs. NGK BKR6E11
Octane booster. (not sure how close to 91 gas is getting during covid so that's some insurance.)

honestly my current setup is a badly crimped 2.5 exhaust onto a 2.25 pipe. time I fixed that.
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  #11  
Old September 1st, 2020, 19:21
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Re: High NOX every year

Silly question.
Anyone else know if there is issues with the Bosch 15704 not correctly mapping to get the cat hot enough?
Might buy an NTK just in case that is my issue.
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  #12  
Old September 1st, 2020, 19:24
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Re: High NOX every year

Reading reviews on this- https://www.amazon.com/NGK-23023-Oxy...ustomerReviews

---

I work for an automotive repair facility that happens to be a STAR station, we see quite a few 4.0 jeeps that come in for smogs and fail for high NOX (800-2000) range, after checking for cat function and exhaust leaks we normally find that the 02 has been recently replaced or may be faulty. for OBD1 4.0 YJ's YOU MUST have an 02 designed to work with that system, we are finding that many denso's and even factory 02 sensors will cause NOX to INCREASE, all because the 02 switches at a much faster rate than the systems were originally designed. We had a jeep come in a request a pre-test, running the jeep on the machine we could see NOX was through the roof (1800-2000) range at 15 and 25mph. after checking for all other causes of failing it was noted that the customer had just changed the 02, after sourcing an NGK which is the OEM ORIGINAL AMC supplier (NOT DENSO) the vehicle passed without further problems. I have fought for 6 years with many other sensors on many other jeeps and will no longer purchase anything OTHER than an NGK.

---
Pretty much having the same findings online.
hmmm. I know I replaced this each time. and adjusting the timing the way I have been doing would technically cause the engine to run a little "hot" so having some thoughts here...
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  #13  
Old September 2nd, 2020, 06:23
tempest411 tempest411 is offline
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Re: High NOX every year

VERY interesting!
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  #14  
Old September 2nd, 2020, 07:39
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Re: High NOX every year

Yeah, get the NTK. Costs more but gets 'er dun!!
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  #15  
Old September 2nd, 2020, 08:44
RCP Phx RCP Phx is online now
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Re: High NOX every year

Quote:
Originally Posted by Black1990jeep View Post
A new cat can do wonders to clean up NOx. A california type cat even more so. I always recommend a new O2 sensor when replacing the cat, as a weak or slow O2 sensor (one that cycles slowly) can poison a new cat pretty quick.

you might want to consider a california type cat for test purposes only, retaining your old cat, or a test pipe for other use where legal to do so of course.
There is no known physical difference other that the "Carb" number!
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