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Discussion Starter · #1 ·
What causes high NO numbers? I passed everything else except NO. Everything is back to stock and the egr is working, what else can cause high NO numbers? Would a turbo ecu and 370cc injectors cause high NO numbers? Please help me out.
 

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You like that, dontchya?
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Are you sure EGR is working? EGR is your best NO killer. You really got to clean it out to get it to work right. Check se-r.net for instructions...

What are your results? Post them, let's see how close you are...
 

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midnight_marauder
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O2 sensor? I had the same problem 2 years ago, the rear oxygen sensor was bad, well, both, on my 98, then I passed smog, but the NO numbers were sorta high. I just got smogged last month, I replaced the spark plug wires, put the stock air box on, and passed with flying colors!!!!
 

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Tired Greasemonkey
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O2 does nothing for nox unless its broken and stuck sending lean voltage to the ecu, whats your timing at?
retarding the timing can lower nox but sometimes cause the co% and hc to go up, was the failing nox reading at the low speed stage or the high?
give me some smog #s to deal with.....
since you are in the bay area they did a functional check on your egr and timing so i'm assuming your timing is at 15 degrees btdc, how did you pass a det in an enhanced area???
 

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I had similar problem in Oregon with a '94 (JDM motor). 2 things from my experience that may help. 1) We know high NOx is a result of higher combustion temperature, higher combustion temp can be caused by a number of things. If your NOx is higher than your CO (measured on the same scale, in OR it's grams / mile) then high NOx is caused (primarily?) by a lean condition. NOx is very sensitive to mixture and must be very near stoichiometric (ideal mixture) to be reduced (catalyzed) effectively. If I understand correctly, if HC and CO are both well within limits and only NOx is high, your catalytic converter is good.

2) In my case -- 3 attempts, NOx was as high as 5.43 grams/mile and CO as low as 0.76 grams / mile, against stds of 3.0 for NOx and 30 for CO. I checked alot of things to try and figure out cause of lean mixture. I never really did. I eventualy (barely) passed by a) cleaning egr really, really well b) setting timing to 15 c) resetting ecu. I also used 92 octane gas (highest I could find) theoretically burns a bit slower ergo lower combustion temps, ergo lower NOx, and I ran a bottle of techron through to try and clean injectors a bit. Don't know that those last 2 did much, because I failed once after those 2, but before the 1st 3. My numbers, when I passed were NOx 2.98 g/m (std is 3.0) CO 5.65 g/m (std is 30) I can't remember right now, but it was well within limits all 4 times I tested.

Hope this helps a little.
 

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Discussion Starter · #8 ·
15mph
HC (ppm): Measured=50 Allowed=124
CO (%): Measured=.11 Allowed=.78
NO (ppm): Measured=1039 Allowed=815

25mph
HC (ppm): Measured=13 Allowed=98
CO (%): Measured=.04 Allowed=.66
NO (ppm): Measured=1074 Allowed=754

The ecu I have is for 8.5:1 compression I have 9.5:1 compression.
 

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Discussion Starter · #10 ·
My base timing was at 15 degrees...I passed everything except for NO. The guy at the smog station did a quick check of my egr system and said it was working. Would the 8.5:1 compression turbo ecu cause me to run lean resulting in higher combustion temps, therefore causing the high NO numbers?
 

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VE powered
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First thing would be to make sure your cat is up to temp. Run the car on the freeway for a good 30 minutes prior to testing so the cat is nice and hot.

Second thing I'd try would be to lower your timing to 13 degs (still within factory spec) which should lower your combustion chamber temps.

Last thing would be to install an exhaust restrictor just before the cat. Make the hole only an inch in diameter. This should force more air thru the EGR system.

Steve
 

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Your cat is clogged, my NOx was 900 a year ago. Replaced the cat (orignial), NOx 15-30 passed with flying colors. Is the cat OEM and has it been changed since you had the car? Replacing your cat will solve you problem. Later.
 

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Tired Greasemonkey
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in my opinion i wouldn't do the exhaust resticor, again how did you pass visual with a det? a new cat may help with your nox, on the emission labe it'll say twc which stands for three way catalytic converter, meaning that it works on the three main smog forming particulates (hcppm,co% and noxppm).
if they are only failing you because of the nox try adding or replacing your cat.
maybe retard the timing to 13. the turbo ecu wouldn't increase your nox, as far as i know.
 

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SE-R Protection League
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My 93 SE-R with 48,000 original miles failed smog twice in the same way.
HC and CO are *below* average, base-timing at 15deg, EGR is not stuck.
I also removed my JWT ECU, and that made the NOx at 25mpg lowered.
Cat in good condition, same cat past smog on my other SE-R recently.
But the NOx at 15mph is over twice the MAX.
NOx at 25mph barely below MAX.

Another clue is (if relevant or not), on a dynojet, this car only makes 119wbhp.
And it was back-firing and bucking at high RPM during the dyno run.
The car has the usual NA bolt-on, like JWT ECU, HS header, HKS intake, Courtesy 2.5" cat-back exhaust, etc.
The compression is good, at about 170psi all across.
Fuel pressure is at about 45psi.


Any suggestion would be greatly appreciated. :biggthump
 

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Bitter Old Man
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Vacuum leak? Running lean will increase combustion temp. Would explain the crappy dyno run.

And (since it was dug up out of the trash) higher octane gasoline does not burn slower!. It's reaction rate is just as great as lower octane fuel. Reaction initiation energy is higher as octane rating increases, but once the reaction is started, they all burn at the same speed, give or take.
 

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i go with the cat, running turbo might mess up your cat already...plus, change the ecu back to stock, i think the 370cc injectors are okay,....but when it comes to nox, your cat is usually the suspect from my experience....
 
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