Question about 1994 Chevrolet G20

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Finally got the HydroCarbs down to pass (1.46 from 2.66- limit 1.60), but now the NOX has jumped four times to 6.45. Previous 1.68 (limit 3.0) Only change was the replacement of spark wires. Help!

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Check the O2 sensors out

Posted on Sep 04, 2010

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1996 dakota 4 cyl. won't pass smog test nox is 225 over limits. Asked smog tech it has no egr. I replaced 02 senser ,flushed cooling system, used seafoam as directed on bottle. All those steps dropped nox...


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be it a intake or exhaust, sounds to me like you found your problem allready,Gary

Oct 24, 2013 | 1998 Dodge Dakota

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Fail smog test


fist i would like you to post the year make and model of the truck along with the HC ppms and NOX ppm it would be very helpful but high hc and nox can be attributed to a faulty EGR system nox is produced when the combustion chamber temperature gets too high so a small amount of exhaust is cycled back into the air stream to help cool them there are other causes but without looking at the levels its much harder to say

Dec 06, 2012 | Cars & Trucks

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SMOG test passed ALL except "NOx" results were 696 Limit is 585. Any easy fixes ??


I've had good luck using CRC's "Guaranteed to pass" fuel system cleaner. Follow the directions exactly. It should bring all the smog numbers down--perhaps get your NOx number low enough.

If the EGR valve is not working properly, it will lead to high NOx. Check for a leaky vacuum diaphragm on this valve. It will not only keep the EGR from working when it should, but also lead to a lean mixture that burns hotter, thus generating even more NOx.

Check for vacuum leaks. Any extra air that makes the mixture lean will contribute to high combustion temperatures and high NOx--even if the EGR valve is working.

Finally, if those steps don't work, it could be your catalytic converter is getting old and inefficient. Don't be surprised if you need a new 'cat.

Feb 27, 2011 | 1987 Acura Legend

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I took my daughters 1995 Nissan Altima for its two year smog inspection and it failed three times due to nox failure at levels around 1400. Back in march of 2009 I took it to a reputable shop and they...


Check the ports if there is any carbon,I doubt it,
but you got to look
I would make sure you don't have overheating issues
That is the cause of NOX (High Combustion Temp)
Check fuel pressure
Use synthetic oil in engine
Check PCV Hoses etc

Feb 06, 2011 | 1995 Nissan Altima

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I got a 95 corsica 2.2L failed emission test the carbon monoxide is too high the hydrocarbons passed but were higher than previous tests and the nox passed but were higher than previous tests...


sounds like a bad cat and o2 sensor. try a scanner, if the downstream sensor is attempting to make a 99% fuel trim adjustment, you can bet it needs changing along with the catalytic converter. get someone to follow you and accelerate hard, a rotton egg smell is a dead giveaway

May 28, 2010 | 1995 Chevrolet Corsica

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1991 olds Cutlass Ciera. 3.3l, failed the NO emission test. Results: HC ppm 12 .......limit 62 CO % 0.09 ..... limit 0.35 NO ppm 948 ..... limit 700 Before testing changed plugs, wires,PCV,oil. Also had...


Since your cat was replaced you should be looking at fuel problems...even gas cap seal....check fuel pressure,fuel regulator,and evap system.>canister or purge solinoid,o2 senser...high nox is caused by the cat or fuel problems on these engines...high pressure in the combustion chamber...lean condition>air leak on hoses,or high compression caused by carbon build up ...there is no EGR on this car so don't waste time looking for it...hope this points you to your problem

Mar 14, 2010 | 1991 Oldsmobile Cutlass Ciera

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2.3 dohc wont pass smog


Did you do a full tune up?
Do a compression test and check for any cyclinder that is low in PSI.
Look of wet plug and oil coated plug(s).
== Which item CO,NOx,Hc is failing?
You may need to repose to add information.
Use a plug non-fouler / protector on the weak cylinder will help if HC is just shy from the passing limit.
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Mar 05, 2010 | 1993 Honda Prelude

1 Answer

New catalytic, can't pass e-test,too much Nox, almost double the limit,temp sticker running out PLEASE HELP! 95 yj 4.0L


Nox is heat related not cat. Your car is running to lean you need to get it to burn more fuel. Check EGR valve.

Dec 20, 2009 | 1995 Jeep Wrangler

1 Answer

Emissions level HC (PPM) too high in truck. How to fix?


Do an oil change with 20W50 oil (or one grade higher) to prevent blow by during the test.

You current oil has HC from blow by though the rings.

Do a fresh oil change will lower the HC.

========
Change spark plugs,wires,cap and rotor if they are over 24,000 miles
========

Make the smog check appointment for the EARLY MORNING. Colder air will help the fuel burn better.

========

Clean or change the air filter and pcv valve.

Clean Mass Air Flow sensor with CRC Mass Air flow cleaner or electronic part cleaner.

========

Do a quick wipe down on the wires and cap to take the moisture off.

========

Check spark plug wire contacts for corrosion.

========

Fill the tank to around 3/4.......just in case your fuel pump is weak.

========

Ran the truck for 20+ minutes on highway before the test.

========

Do not carry excessive cargo on the truck bed.


These are the little things I would do to get the HC and CO down.


Please post more information on the comment window.

Jul 16, 2008 | 1990 Ford F250

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