# '94 Sentra Fails Smog



## VonRipon (Aug 28, 2006)

My 94 Sentra failed a smog test. I tuned it up, replaced the fuel filter and CAT, cleaned the injectors and still fails. The NOX is too high at 15 mph. Any suggestions?


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## notoriousbob (Aug 7, 2006)

VonRipon said:


> My 94 Sentra failed a smog test. I tuned it up, replaced the fuel filter and CAT, cleaned the injectors and still fails. The NOX is too high at 15 mph. Any suggestions?



Gap your plugs. Sounds like they may be burning too hot? Too hot a burn is what causes NOX isnt it? Anyways, the plugs are usually suspect in most emissions problems.

-Bob


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## xXDynamosXx (Aug 29, 2006)

That or the O2 Sensor


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## sunnysentra (Jul 24, 2002)

replace the 02 sensor. Replace the cap and rotor. The ignition coil could be weak also, maybe try a new coil or a known good coil. new ones from Nissan are not cheap. 

Also, make sure the EGR is clean and working well. the BPT valve should be clean and free of carbon. Also, run the thing after the tuneup with BG TDR or 44K total deposit removal. its a can you dump into the tank. that removes all combustion chamber deposits. 

You need to really make sure the spark is good and the O2 sensor is working well. I would suggest getting a Nissan consult to see if that 02 is working or not. it will tell you also if the injectors are leaking. if this is the case, then you can dump hydrocarbons from unburned gas into the cat to throw off the NOX and hydrocarbons. 

Chris 92 classic


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## EvilPotato (Sep 6, 2005)

this post might help you http://www.nissanforums.com/b14-95-99-chassis/125302-need-help-pass-ca-smog-test.html


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## tmcnally (Jun 23, 2005)

what EXACTLY did you do for your tune up?


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## tmcnally (Jun 23, 2005)

and when I took possession of my '94 Sentra 6 months ago from my sister it failed NJ emissions. I replaced PCV valve, plugs (OEM gapped properly), spark plug wires, fuel filter, battery (was dead...replaced b4 emissions test...probably no effect), cap and rotor. Luckily it passed. After that I woulda checked timing...cleaned IACV...cleaned throttle body...checked EGR operation....replaced O2 sensor....replaced water temp. sensor...etc.


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## lifeownedme (Jun 20, 2004)

did you touch your timing?


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## srh007 (Nov 6, 2006)

I had the same problem - NOX fail. It turned out for me it was a split in the little rubber hose from the EGR valve to the PCP(?) valve. I'd make sure all those little hoses are intact.


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## b13pnoysentra (Mar 30, 2005)

notoriousbob said:


> Gap your plugs. Sounds like they may be burning too hot? Too hot a burn is what causes NOX isnt it? Anyways, the plugs are usually suspect in most emissions problems.
> 
> -Bob


I don't have sentra manual in my car. Can you tell me what the measurements are for the gap distance again?
Never mind. Searched and found it for 0.039mm - 0.043mm.


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## i3ulldog (Oct 29, 2006)

NOX is formed inside an engine when combustion temperatures exceed 2500 degrees Fahrenheit. NOX is considered to be a serious air pollutant because it is so irritating. NOX emissions are minimized by the EGR valve, and by the catalytic converter in 1981 and newer model cars.

NOX is also only created when the vehicle is under a load...


So i'd be looking at the EGR system, check your EGR valve.


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