california emmissions and NOx

tbird91sc

Registered User
well - its that time again and the last time (two years ago) my nox out put was 834 ppm with a max of 861 ppm allowed at 25 mph. every thing else is well within specs. that was with a 75mm tb, 76mm maf and 42 lbs injectors plus this vehicle is an auto converted to a manual still using the auto computer if that means anything. i am concerned about going over even tho i only put about 1500 miles a year on the car. my cats and 02 sensors have less than 5K on them. i researched old postings and will pop in a new motorcraft pvc and check for leaks and i dont have an egr (as per factory). i am curious if putting on the stock maf and tb would help any. since that time i also added an apten chip - i was planning on just pulling it -but- maybe leaving it in is a help instead of a hinderance??? any comments or suggestions will be greatly appreciated.
 
High amounts of NOx are caused by high combustion temps. You might be running a little lean. Changing the MAF should not increase the temp of the combustion if the correct amount of fuel is also being injected into the cylinder. The other mods you have done to your car might be causing the car to run lean.

Hope this helps,
Good luck
 
well - according to my air/fuel guage i am only lean when i back off the throttle - now how accurate these guages are i dont know. but i would like to know what is your logic for a lean condition when the injectors have been increased from 30# to 42# and wouldnt i be throwing a code if too lean. and does any one know the the stock nox output was supposed to be?
 
tbird91sc said:
well - according to my air/fuel guage i am only lean when i back off the throttle - now how accurate these guages are i dont know. but i would like to know what is your logic for a lean condition when the injectors have been increased from 30# to 42# and wouldnt i be throwing a code if too lean. and does any one know the the stock nox output was supposed to be?

I also have a 91 tbird (5-speed) all stock and have been battling high Nox readings for the past 2 weeks. Now I need to take it to a state certified testing and repair garage to get it looked at. Since failing my first test, I've replaced cats, o2 sensors and still comes back with very high NOx results, almost double the max. The car is running great, no check engine nor any codes from my code reader. Don't know what else to do but take it to the place and pay em' $125 to look at it. It has a rebuilt motor only 18k on it. :mad: I've found many identical posts here but few positive results. One post spoke of cleaning MAF wires (which I have done) and oil change, new spark plugs, etc... Not sure what else to look at, the engine is clean inside and out. I realized Nox is due to high combustion temps. but no real concrete ways to lower it.. ok, I am rambling... Just frustrated.
 
i just remembered i added in mikes aluminum radiator too since my last check so i am running awhole lot cooler - on would think that would help too
also - going to the state testing and repair - what do you do - just pay the 350 max or so for them to try and fix it and then they pass you whether you pass or not??
 
Do a KOER test.. look for knock sensor problems. I just read that over-advanced timing can cause higher Nox levels. I have a similar problem and got the code even though I had no running problems, no knocking, no check engine light, and no memory code :(

I don't know if this will fix my borderline nox problem, but it might.

Other than that, check for vaccuum leaks.
 
What was the code #? because I also ran the KOER tests and received OK codes like 111 then ran cylinder by cylinder tests and I got a 90 which meant all cylinders were firing correctly. No other codes to speak of.
 
My test results should be attached. They won't help you a lot, but will show how low Nox can go. This is from a new (not rebuild) engine and new cats. The engine was a new 1990 crate motor I found last Oct. and installed in May. It had new everything, sensors, blower, wires, etc. It was complete. I used a set of Catco direct replacement cats and pipes. Looked almost original except the left cat had a nice pipe going into it instead of 90 deg used on the stock cat. This is about as stock as you can get.
One thing I noticed this year the max nox allowed was lower then it was 2 years ago. At least it was here in San Diego.
 

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thanks - its down about 150 ppm from what i had to meet two years ago - if it is that way in orange county - i am in trouble
iaragon - what is the mas nox ppms you have to meet?
jim
 
I don't have it in front of me right now, but I believe it was 868 max at 15mph and I forget the other. Funny thing though, I've test at two stations and its been between 150ppm over to about 800ppm over. So, its not real consistent. I have had it tested a total of 5 times at these two stations (4 at one and once at the other) At all times the engine was hot, running supreme (91 octane for us in California) and they had a fan running in front of the car. What I should have tried was removing that octane plug everyone seems to talk about.
 
when i tested in 2000 and 2002, it was a max of 1001 at 15 mph and 861 at 25 mph. i am going to run by the smog guy today to see if it has changed. i did notice i was in the 500s pre 42 lbs injectors, 75 tb and 76 mass and in the 800s with - so i think i am going to at least put the stock t/b and mass back in and hope the computer will compensate and run a short duty cycle on the 42 injectors. i also put headers on too so my cats are a tad back further too but not too bad. would it be worth getting about 5 gallons of union racing gas too. it take it the octane plug is the knock sensor??? i was also thinking if i was close that i could try different stations - we are talking part per MILLION here. also made an 9 am appointment so i will get there at eight and let the engine cool down too. my wife says this may be the excuse we need to finally get the hell out of california.
 
tbird91sc said:
it take it the octane plug is the knock sensor???
No. The octane plug is a jumper in the wire harness which tells the EEC not to adjust the timing when you're running bad gas. Most people don't know anything about it; its not covered in the owner's manual that I know of and nothing in the Haynes manual that I know about either.
 
oohhh - i just knew it as the "thingy" you pull to adjust the timing. i take it cutting back the timing redudes the cylinder temp?
 
Smog Update

Took my car to a state certified station. They ran their fuel injection cleaner through the system and it passed. Cost $200 :mad: but it passed.
 
well - thats still good news you passed. did the cleaning dramatically change your nox output or did you just squeak by. my injectors have less that 2500 so i hope they dont need cleaning. my appointment is 9 am tomorrow so i am crossing my fingers and hoping for the best
 
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