1997 Nissan Pathfinder high NOX failed smog

[quaint bucket]

Ok, I am having a lot of trouble with my pathfinder passing smog and I am literally stumped. I am taking it to a mechanic to do a professional diagnose because I don't know where to go from here.

My NOX is high and my HC and CO is fine.

I have done the following in this order:

1) inspect and clean EGR. It wasn't gunked up or anything.
2) sea foam intake manifold

Took it to smog again and the test results got worse. Huh???

3) inspect and clean MAF sensor
4) found vacuum leak on air intake duct boot to intake manifold
5) replaced spark plugs
6) replaced spark plug wire
7) replaced dist. Cap
8) replaced dist rotor
9) replaced fuel filter
10) replaced air filter
11) check for exhaust leak (none...)
12) relocated knock sensor (threw a code)

No codes anymore. Took it to smog test after driving 150km. Failed aircare but not as... Horrible? Still no codes.

I'm at loss for words.




Any ideas? The vacuum leak was brutal (two major cracks) that threw p0171. I'm starting to think I should just throw in acetone in the fuel tank just to cheat. Any ideas??

[Leo1998]

In the state i used to live in they called it DEQ and I never looked forward in my 1977 freshly built 6.6L with no cats, just dual flowmasters and a torque cam, I would turn my fuel almost off just so i can listen to it lope inside the building, never understood why every 2 years i had to give them money for a non-catalyst truck! Anyways,
What about the catalytic converter? I don't see that on the list...I found this AirCare thing maybe give it a look.

http://www.aircare.ca/repinfo-ere-causes-nox.php

[atraudes]

What I'm finding (which I'm sure you know) is that high no2 is caused by a defective EGR system, bad catalytic converters, or high combustion temperatures. If the catalytic converters were going bad, I would expect the system to catch that and throw a code.

My best guess is that the timing is simply off, and likely running lean.

Where's the temp needle when it's fully warmed up? It ought to be just below halfway.

[quaint bucket]

I agree, if it was the cat I would fully expect to throw a code like p0420 or something similar. Same thing with the 02 sensor.

My mind keep going back to the timing and/or running lean. Again, I would expect a code for that so I was completely lost.

Mechanic looked over the car with a basic diagnosis all over again. The system was unfortunately not ready so he could not do a full diagnosis (02 and EVAP). He did however pulled out the MAF sensor and saw that it was completely caked with gunk. It makes a lot of sense why it wouldn't pull a code because it was just... coated. He found this based on the fuel trim between -10 to -15%. Yes negative percentage.

I did not clean it as well as I had thought. I held myself back because I was worried about damaging that sensor. Took it out for a drive to get the system ready. Drove 200km following the FSM directions.

The throttle was so much more refined and cleaner. I was actually able to floor the pathfinder without ANY HESISTATION OR STALLS. Literally night and day. With 200km, I only used 1/4 a tank instead of close to 1/2 a tank. Big difference for me.

New codes popped up. P0440 & P0446. EVAP, small leak. Took it to the mechanic, he was going to do a smoke test but opt to look at the valves. One was defective according to him. I refused to replace it ($173 no thanks).


Took it to aircare against the mechanic's advice.


PASSED AIRCARE. My numbers was literally night and day and was just as good as 2003 number posted above. I'm ecstatic.

Lesson of the story: still stuck? Go back to square one. CHECK THE MASS AIR FLOW SENSOR. unbelievable, I feel dumb.

[atraudes]

Wow, awesome to hear it worked out so well!

Sadly they don't throw warnings for rich/lean conditions. Mine was (hopefully isn't any more) running really rich for so long it cooked the catalytic converters, but never threw a code or warning of any sort.

[Leo1998]

On your new code http://engine-codes.com/p0441_nissan.html
Make sure gas cap is tight.

You can try this: First, my code was a P1444 and it also deals with a problem in the EVAP system. I pulled the Purge Volume Control Valve off and blew into an open port to see if it was stuck open. If you can blow through it freely then it is plugged and stuck open, if you can NOT blow through it then it is okay.
Mine was plugged, so i tapped it with my wrench do dislodge the tiny charcoal piece that made it stick open, after that i put it back on. I then installed a clear plastic fuel filter into the line near the Purge Port. (by the brake Master Cylinder, it has a cap on it)
By doing that it will catch any more charcoal from reaching the Purge Volume Control Valve and throwing a code.

Pics of the fuel filter charcoal catcher.
http://leo1998.imgur.com/all/

[Leo1998]

New link

[quaint bucket]

Looks like an interesting modification.

I checked my fuel cap first (removed, inspected for damage, and put it back on with multiple clicks). I looked under the EVAP syst in the rear wheel well. The purge valve is stuck open. I'm goin to pull it this weekend depending on time and soak it in gasoline or some solvent. Then blow out whatever build up is there.

Then I will try to see if I can do a self improvised smoke test to check for any small leaks. I think I found one that looks like a crack in the pipe but can't really tell because I didn't have my magnifying glass on me to look. Can only do so much from under the truck on my back haha. If a part is busted then I will junkyard it because it is not a critical component for my pathy. Jus want to get rid of the CEL.

I'm just happy I passed aircare. Happy that y cats are working phenomenal without having to replace anything and the o2 sensors. How often souls the MAF sensor be cleaned? Everytime I replace the air filter?

First thing first though, I need to take to NISSAN for those TSB kn the rust, filler tube, and seat belts.

If they deem it unsafe and take it... Well I'm just gonna be livid. Once that is done, then I will replace the timing belt, water pump, and thermostat. Then the valve cover gasket (leaking a little oil). Then look into replacing the struts and shocks if I need to. Bushings definitely need to be replaced soon. They don't look pretty.

Once that's all done, then the huntin rig revamp fun will start next year. Budget needs to recover.

[Leo1998]

I'm wondering about the MAF cleaning too.
on that modified charcoal canister filter, its not collecting anymore pieces and I'm thinking about removing it and see what happens. I think inside the charcoal canister a small chunk came apart and the rest of it is still intact.

[atraudes]

I looked into the recommended frequency of MAF cleaning, and the general consensus I found here was every time you change your oil. It's likely overkill, but for such a simple thing, why not?